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90913985b6
The comment about the collection rules for the permanent generation was incorrectly referenced by a comment in gcmodule.c (the comment has been moved long ago into a header file). Moving the comment into the relevant code helps with readability and avoids broken references.
2307 lines
76 KiB
C
2307 lines
76 KiB
C
/*
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Reference Cycle Garbage Collection
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==================================
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Neil Schemenauer <nas@arctrix.com>
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Based on a post on the python-dev list. Ideas from Guido van Rossum,
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Eric Tiedemann, and various others.
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http://www.arctrix.com/nas/python/gc/
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The following mailing list threads provide a historical perspective on
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the design of this module. Note that a fair amount of refinement has
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occurred since those discussions.
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http://mail.python.org/pipermail/python-dev/2000-March/002385.html
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http://mail.python.org/pipermail/python-dev/2000-March/002434.html
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http://mail.python.org/pipermail/python-dev/2000-March/002497.html
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For a highlevel view of the collection process, read the collect
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function.
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*/
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#include "Python.h"
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#include "pycore_context.h"
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#include "pycore_initconfig.h"
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#include "pycore_object.h"
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#include "pycore_pyerrors.h"
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#include "pycore_pymem.h"
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#include "pycore_pystate.h"
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#include "frameobject.h" /* for PyFrame_ClearFreeList */
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#include "pydtrace.h"
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#include "pytime.h" /* for _PyTime_GetMonotonicClock() */
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typedef struct _gc_runtime_state GCState;
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/*[clinic input]
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module gc
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[clinic start generated code]*/
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/*[clinic end generated code: output=da39a3ee5e6b4b0d input=b5c9690ecc842d79]*/
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#ifdef Py_DEBUG
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# define GC_DEBUG
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#endif
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#define GC_NEXT _PyGCHead_NEXT
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#define GC_PREV _PyGCHead_PREV
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// update_refs() set this bit for all objects in current generation.
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// subtract_refs() and move_unreachable() uses this to distinguish
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// visited object is in GCing or not.
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//
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// move_unreachable() removes this flag from reachable objects.
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// Only unreachable objects have this flag.
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//
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// No objects in interpreter have this flag after GC ends.
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#define PREV_MASK_COLLECTING _PyGC_PREV_MASK_COLLECTING
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// Lowest bit of _gc_next is used for UNREACHABLE flag.
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//
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// This flag represents the object is in unreachable list in move_unreachable()
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//
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// Although this flag is used only in move_unreachable(), move_unreachable()
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// doesn't clear this flag to skip unnecessary iteration.
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// move_legacy_finalizers() removes this flag instead.
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// Between them, unreachable list is not normal list and we can not use
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// most gc_list_* functions for it.
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#define NEXT_MASK_UNREACHABLE (1)
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/* Get an object's GC head */
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#define AS_GC(o) ((PyGC_Head *)(o)-1)
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/* Get the object given the GC head */
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#define FROM_GC(g) ((PyObject *)(((PyGC_Head *)g)+1))
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static inline int
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gc_is_collecting(PyGC_Head *g)
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{
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return (g->_gc_prev & PREV_MASK_COLLECTING) != 0;
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}
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static inline void
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gc_clear_collecting(PyGC_Head *g)
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{
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g->_gc_prev &= ~PREV_MASK_COLLECTING;
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}
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static inline Py_ssize_t
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gc_get_refs(PyGC_Head *g)
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{
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return (Py_ssize_t)(g->_gc_prev >> _PyGC_PREV_SHIFT);
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}
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static inline void
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gc_set_refs(PyGC_Head *g, Py_ssize_t refs)
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{
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g->_gc_prev = (g->_gc_prev & ~_PyGC_PREV_MASK)
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| ((uintptr_t)(refs) << _PyGC_PREV_SHIFT);
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}
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static inline void
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gc_reset_refs(PyGC_Head *g, Py_ssize_t refs)
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{
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g->_gc_prev = (g->_gc_prev & _PyGC_PREV_MASK_FINALIZED)
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| PREV_MASK_COLLECTING
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| ((uintptr_t)(refs) << _PyGC_PREV_SHIFT);
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}
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static inline void
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gc_decref(PyGC_Head *g)
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{
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_PyObject_ASSERT_WITH_MSG(FROM_GC(g),
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gc_get_refs(g) > 0,
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"refcount is too small");
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g->_gc_prev -= 1 << _PyGC_PREV_SHIFT;
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}
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/* Python string to use if unhandled exception occurs */
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static PyObject *gc_str = NULL;
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/* set for debugging information */
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#define DEBUG_STATS (1<<0) /* print collection statistics */
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#define DEBUG_COLLECTABLE (1<<1) /* print collectable objects */
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#define DEBUG_UNCOLLECTABLE (1<<2) /* print uncollectable objects */
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#define DEBUG_SAVEALL (1<<5) /* save all garbage in gc.garbage */
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#define DEBUG_LEAK DEBUG_COLLECTABLE | \
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DEBUG_UNCOLLECTABLE | \
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DEBUG_SAVEALL
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#define GEN_HEAD(gcstate, n) (&(gcstate)->generations[n].head)
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void
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_PyGC_InitState(GCState *gcstate)
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{
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gcstate->enabled = 1; /* automatic collection enabled? */
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#define _GEN_HEAD(n) GEN_HEAD(gcstate, n)
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struct gc_generation generations[NUM_GENERATIONS] = {
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/* PyGC_Head, threshold, count */
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{{(uintptr_t)_GEN_HEAD(0), (uintptr_t)_GEN_HEAD(0)}, 700, 0},
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{{(uintptr_t)_GEN_HEAD(1), (uintptr_t)_GEN_HEAD(1)}, 10, 0},
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{{(uintptr_t)_GEN_HEAD(2), (uintptr_t)_GEN_HEAD(2)}, 10, 0},
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};
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for (int i = 0; i < NUM_GENERATIONS; i++) {
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gcstate->generations[i] = generations[i];
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};
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gcstate->generation0 = GEN_HEAD(gcstate, 0);
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struct gc_generation permanent_generation = {
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{(uintptr_t)&gcstate->permanent_generation.head,
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(uintptr_t)&gcstate->permanent_generation.head}, 0, 0
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};
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gcstate->permanent_generation = permanent_generation;
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}
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PyStatus
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_PyGC_Init(PyThreadState *tstate)
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{
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GCState *gcstate = &tstate->interp->gc;
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if (gcstate->garbage == NULL) {
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gcstate->garbage = PyList_New(0);
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if (gcstate->garbage == NULL) {
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return _PyStatus_NO_MEMORY();
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}
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}
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return _PyStatus_OK();
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}
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/*
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_gc_prev values
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---------------
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Between collections, _gc_prev is used for doubly linked list.
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Lowest two bits of _gc_prev are used for flags.
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PREV_MASK_COLLECTING is used only while collecting and cleared before GC ends
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or _PyObject_GC_UNTRACK() is called.
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During a collection, _gc_prev is temporary used for gc_refs, and the gc list
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is singly linked until _gc_prev is restored.
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gc_refs
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At the start of a collection, update_refs() copies the true refcount
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to gc_refs, for each object in the generation being collected.
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subtract_refs() then adjusts gc_refs so that it equals the number of
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times an object is referenced directly from outside the generation
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being collected.
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PREV_MASK_COLLECTING
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Objects in generation being collected are marked PREV_MASK_COLLECTING in
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update_refs().
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_gc_next values
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---------------
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_gc_next takes these values:
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0
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The object is not tracked
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!= 0
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Pointer to the next object in the GC list.
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Additionally, lowest bit is used temporary for
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NEXT_MASK_UNREACHABLE flag described below.
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NEXT_MASK_UNREACHABLE
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move_unreachable() then moves objects not reachable (whether directly or
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indirectly) from outside the generation into an "unreachable" set and
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set this flag.
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Objects that are found to be reachable have gc_refs set to 1.
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When this flag is set for the reachable object, the object must be in
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"unreachable" set.
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The flag is unset and the object is moved back to "reachable" set.
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move_legacy_finalizers() will remove this flag from "unreachable" set.
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*/
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/*** list functions ***/
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static inline void
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gc_list_init(PyGC_Head *list)
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{
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// List header must not have flags.
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// We can assign pointer by simple cast.
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list->_gc_prev = (uintptr_t)list;
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list->_gc_next = (uintptr_t)list;
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}
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static inline int
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gc_list_is_empty(PyGC_Head *list)
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{
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return (list->_gc_next == (uintptr_t)list);
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}
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/* Append `node` to `list`. */
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static inline void
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gc_list_append(PyGC_Head *node, PyGC_Head *list)
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{
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PyGC_Head *last = (PyGC_Head *)list->_gc_prev;
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// last <-> node
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_PyGCHead_SET_PREV(node, last);
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_PyGCHead_SET_NEXT(last, node);
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// node <-> list
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_PyGCHead_SET_NEXT(node, list);
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list->_gc_prev = (uintptr_t)node;
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}
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/* Remove `node` from the gc list it's currently in. */
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static inline void
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gc_list_remove(PyGC_Head *node)
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{
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PyGC_Head *prev = GC_PREV(node);
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PyGC_Head *next = GC_NEXT(node);
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_PyGCHead_SET_NEXT(prev, next);
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_PyGCHead_SET_PREV(next, prev);
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node->_gc_next = 0; /* object is not currently tracked */
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}
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/* Move `node` from the gc list it's currently in (which is not explicitly
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* named here) to the end of `list`. This is semantically the same as
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* gc_list_remove(node) followed by gc_list_append(node, list).
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*/
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static void
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gc_list_move(PyGC_Head *node, PyGC_Head *list)
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{
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/* Unlink from current list. */
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PyGC_Head *from_prev = GC_PREV(node);
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PyGC_Head *from_next = GC_NEXT(node);
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_PyGCHead_SET_NEXT(from_prev, from_next);
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_PyGCHead_SET_PREV(from_next, from_prev);
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/* Relink at end of new list. */
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// list must not have flags. So we can skip macros.
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PyGC_Head *to_prev = (PyGC_Head*)list->_gc_prev;
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_PyGCHead_SET_PREV(node, to_prev);
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_PyGCHead_SET_NEXT(to_prev, node);
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list->_gc_prev = (uintptr_t)node;
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_PyGCHead_SET_NEXT(node, list);
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}
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/* append list `from` onto list `to`; `from` becomes an empty list */
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static void
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gc_list_merge(PyGC_Head *from, PyGC_Head *to)
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{
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assert(from != to);
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if (!gc_list_is_empty(from)) {
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PyGC_Head *to_tail = GC_PREV(to);
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PyGC_Head *from_head = GC_NEXT(from);
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PyGC_Head *from_tail = GC_PREV(from);
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assert(from_head != from);
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assert(from_tail != from);
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_PyGCHead_SET_NEXT(to_tail, from_head);
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_PyGCHead_SET_PREV(from_head, to_tail);
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_PyGCHead_SET_NEXT(from_tail, to);
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_PyGCHead_SET_PREV(to, from_tail);
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}
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gc_list_init(from);
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}
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static Py_ssize_t
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gc_list_size(PyGC_Head *list)
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{
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PyGC_Head *gc;
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Py_ssize_t n = 0;
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for (gc = GC_NEXT(list); gc != list; gc = GC_NEXT(gc)) {
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n++;
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}
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return n;
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}
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/* Walk the list and mark all objects as non-collecting */
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static inline void
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gc_list_clear_collecting(PyGC_Head *collectable)
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{
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PyGC_Head *gc;
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for (gc = GC_NEXT(collectable); gc != collectable; gc = GC_NEXT(gc)) {
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gc_clear_collecting(gc);
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}
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}
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/* Append objects in a GC list to a Python list.
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* Return 0 if all OK, < 0 if error (out of memory for list)
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*/
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static int
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append_objects(PyObject *py_list, PyGC_Head *gc_list)
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{
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PyGC_Head *gc;
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for (gc = GC_NEXT(gc_list); gc != gc_list; gc = GC_NEXT(gc)) {
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PyObject *op = FROM_GC(gc);
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if (op != py_list) {
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if (PyList_Append(py_list, op)) {
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return -1; /* exception */
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}
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}
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}
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return 0;
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}
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// Constants for validate_list's flags argument.
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enum flagstates {collecting_clear_unreachable_clear,
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collecting_clear_unreachable_set,
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collecting_set_unreachable_clear,
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collecting_set_unreachable_set};
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#ifdef GC_DEBUG
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// validate_list checks list consistency. And it works as document
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// describing when flags are expected to be set / unset.
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// `head` must be a doubly-linked gc list, although it's fine (expected!) if
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// the prev and next pointers are "polluted" with flags.
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// What's checked:
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// - The `head` pointers are not polluted.
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// - The objects' PREV_MASK_COLLECTING and NEXT_MASK_UNREACHABLE flags are all
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// `set or clear, as specified by the 'flags' argument.
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// - The prev and next pointers are mutually consistent.
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static void
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validate_list(PyGC_Head *head, enum flagstates flags)
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{
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assert((head->_gc_prev & PREV_MASK_COLLECTING) == 0);
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assert((head->_gc_next & NEXT_MASK_UNREACHABLE) == 0);
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uintptr_t prev_value = 0, next_value = 0;
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switch (flags) {
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case collecting_clear_unreachable_clear:
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break;
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case collecting_set_unreachable_clear:
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prev_value = PREV_MASK_COLLECTING;
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break;
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case collecting_clear_unreachable_set:
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next_value = NEXT_MASK_UNREACHABLE;
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break;
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case collecting_set_unreachable_set:
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prev_value = PREV_MASK_COLLECTING;
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next_value = NEXT_MASK_UNREACHABLE;
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break;
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default:
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assert(! "bad internal flags argument");
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}
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PyGC_Head *prev = head;
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PyGC_Head *gc = GC_NEXT(head);
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while (gc != head) {
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PyGC_Head *trueprev = GC_PREV(gc);
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PyGC_Head *truenext = (PyGC_Head *)(gc->_gc_next & ~NEXT_MASK_UNREACHABLE);
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assert(truenext != NULL);
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assert(trueprev == prev);
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assert((gc->_gc_prev & PREV_MASK_COLLECTING) == prev_value);
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assert((gc->_gc_next & NEXT_MASK_UNREACHABLE) == next_value);
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prev = gc;
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gc = truenext;
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}
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assert(prev == GC_PREV(head));
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}
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#else
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#define validate_list(x, y) do{}while(0)
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#endif
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/*** end of list stuff ***/
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/* Set all gc_refs = ob_refcnt. After this, gc_refs is > 0 and
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* PREV_MASK_COLLECTING bit is set for all objects in containers.
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*/
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static void
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update_refs(PyGC_Head *containers)
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{
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PyGC_Head *gc = GC_NEXT(containers);
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for (; gc != containers; gc = GC_NEXT(gc)) {
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gc_reset_refs(gc, Py_REFCNT(FROM_GC(gc)));
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/* Python's cyclic gc should never see an incoming refcount
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* of 0: if something decref'ed to 0, it should have been
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* deallocated immediately at that time.
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* Possible cause (if the assert triggers): a tp_dealloc
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* routine left a gc-aware object tracked during its teardown
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* phase, and did something-- or allowed something to happen --
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* that called back into Python. gc can trigger then, and may
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* see the still-tracked dying object. Before this assert
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* was added, such mistakes went on to allow gc to try to
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* delete the object again. In a debug build, that caused
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* a mysterious segfault, when _Py_ForgetReference tried
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* to remove the object from the doubly-linked list of all
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* objects a second time. In a release build, an actual
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* double deallocation occurred, which leads to corruption
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* of the allocator's internal bookkeeping pointers. That's
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* so serious that maybe this should be a release-build
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* check instead of an assert?
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*/
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_PyObject_ASSERT(FROM_GC(gc), gc_get_refs(gc) != 0);
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}
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}
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|
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/* A traversal callback for subtract_refs. */
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static int
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visit_decref(PyObject *op, void *parent)
|
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{
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_PyObject_ASSERT(_PyObject_CAST(parent), !_PyObject_IsFreed(op));
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|
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if (PyObject_IS_GC(op)) {
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PyGC_Head *gc = AS_GC(op);
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/* We're only interested in gc_refs for objects in the
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* generation being collected, which can be recognized
|
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* because only they have positive gc_refs.
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*/
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if (gc_is_collecting(gc)) {
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gc_decref(gc);
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}
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}
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return 0;
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}
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|
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/* Subtract internal references from gc_refs. After this, gc_refs is >= 0
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* for all objects in containers, and is GC_REACHABLE for all tracked gc
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* objects not in containers. The ones with gc_refs > 0 are directly
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* reachable from outside containers, and so can't be collected.
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*/
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static void
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subtract_refs(PyGC_Head *containers)
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{
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traverseproc traverse;
|
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PyGC_Head *gc = GC_NEXT(containers);
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for (; gc != containers; gc = GC_NEXT(gc)) {
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PyObject *op = FROM_GC(gc);
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traverse = Py_TYPE(op)->tp_traverse;
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(void) traverse(FROM_GC(gc),
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(visitproc)visit_decref,
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op);
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}
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}
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|
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/* A traversal callback for move_unreachable. */
|
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static int
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visit_reachable(PyObject *op, PyGC_Head *reachable)
|
|
{
|
|
if (!PyObject_IS_GC(op)) {
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return 0;
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}
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PyGC_Head *gc = AS_GC(op);
|
|
const Py_ssize_t gc_refs = gc_get_refs(gc);
|
|
|
|
// Ignore objects in other generation.
|
|
// This also skips objects "to the left" of the current position in
|
|
// move_unreachable's scan of the 'young' list - they've already been
|
|
// traversed, and no longer have the PREV_MASK_COLLECTING flag.
|
|
if (! gc_is_collecting(gc)) {
|
|
return 0;
|
|
}
|
|
// It would be a logic error elsewhere if the collecting flag were set on
|
|
// an untracked object.
|
|
assert(gc->_gc_next != 0);
|
|
|
|
if (gc->_gc_next & NEXT_MASK_UNREACHABLE) {
|
|
/* This had gc_refs = 0 when move_unreachable got
|
|
* to it, but turns out it's reachable after all.
|
|
* Move it back to move_unreachable's 'young' list,
|
|
* and move_unreachable will eventually get to it
|
|
* again.
|
|
*/
|
|
// Manually unlink gc from unreachable list because the list functions
|
|
// don't work right in the presence of NEXT_MASK_UNREACHABLE flags.
|
|
PyGC_Head *prev = GC_PREV(gc);
|
|
PyGC_Head *next = (PyGC_Head*)(gc->_gc_next & ~NEXT_MASK_UNREACHABLE);
|
|
_PyObject_ASSERT(FROM_GC(prev),
|
|
prev->_gc_next & NEXT_MASK_UNREACHABLE);
|
|
_PyObject_ASSERT(FROM_GC(next),
|
|
next->_gc_next & NEXT_MASK_UNREACHABLE);
|
|
prev->_gc_next = gc->_gc_next; // copy NEXT_MASK_UNREACHABLE
|
|
_PyGCHead_SET_PREV(next, prev);
|
|
|
|
gc_list_append(gc, reachable);
|
|
gc_set_refs(gc, 1);
|
|
}
|
|
else if (gc_refs == 0) {
|
|
/* This is in move_unreachable's 'young' list, but
|
|
* the traversal hasn't yet gotten to it. All
|
|
* we need to do is tell move_unreachable that it's
|
|
* reachable.
|
|
*/
|
|
gc_set_refs(gc, 1);
|
|
}
|
|
/* Else there's nothing to do.
|
|
* If gc_refs > 0, it must be in move_unreachable's 'young'
|
|
* list, and move_unreachable will eventually get to it.
|
|
*/
|
|
else {
|
|
_PyObject_ASSERT_WITH_MSG(op, gc_refs > 0, "refcount is too small");
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
/* Move the unreachable objects from young to unreachable. After this,
|
|
* all objects in young don't have PREV_MASK_COLLECTING flag and
|
|
* unreachable have the flag.
|
|
* All objects in young after this are directly or indirectly reachable
|
|
* from outside the original young; and all objects in unreachable are
|
|
* not.
|
|
*
|
|
* This function restores _gc_prev pointer. young and unreachable are
|
|
* doubly linked list after this function.
|
|
* But _gc_next in unreachable list has NEXT_MASK_UNREACHABLE flag.
|
|
* So we can not gc_list_* functions for unreachable until we remove the flag.
|
|
*/
|
|
static void
|
|
move_unreachable(PyGC_Head *young, PyGC_Head *unreachable)
|
|
{
|
|
// previous elem in the young list, used for restore gc_prev.
|
|
PyGC_Head *prev = young;
|
|
PyGC_Head *gc = GC_NEXT(young);
|
|
|
|
/* Invariants: all objects "to the left" of us in young are reachable
|
|
* (directly or indirectly) from outside the young list as it was at entry.
|
|
*
|
|
* All other objects from the original young "to the left" of us are in
|
|
* unreachable now, and have NEXT_MASK_UNREACHABLE. All objects to the
|
|
* left of us in 'young' now have been scanned, and no objects here
|
|
* or to the right have been scanned yet.
|
|
*/
|
|
|
|
while (gc != young) {
|
|
if (gc_get_refs(gc)) {
|
|
/* gc is definitely reachable from outside the
|
|
* original 'young'. Mark it as such, and traverse
|
|
* its pointers to find any other objects that may
|
|
* be directly reachable from it. Note that the
|
|
* call to tp_traverse may append objects to young,
|
|
* so we have to wait until it returns to determine
|
|
* the next object to visit.
|
|
*/
|
|
PyObject *op = FROM_GC(gc);
|
|
traverseproc traverse = Py_TYPE(op)->tp_traverse;
|
|
_PyObject_ASSERT_WITH_MSG(op, gc_get_refs(gc) > 0,
|
|
"refcount is too small");
|
|
// NOTE: visit_reachable may change gc->_gc_next when
|
|
// young->_gc_prev == gc. Don't do gc = GC_NEXT(gc) before!
|
|
(void) traverse(op,
|
|
(visitproc)visit_reachable,
|
|
(void *)young);
|
|
// relink gc_prev to prev element.
|
|
_PyGCHead_SET_PREV(gc, prev);
|
|
// gc is not COLLECTING state after here.
|
|
gc_clear_collecting(gc);
|
|
prev = gc;
|
|
}
|
|
else {
|
|
/* This *may* be unreachable. To make progress,
|
|
* assume it is. gc isn't directly reachable from
|
|
* any object we've already traversed, but may be
|
|
* reachable from an object we haven't gotten to yet.
|
|
* visit_reachable will eventually move gc back into
|
|
* young if that's so, and we'll see it again.
|
|
*/
|
|
// Move gc to unreachable.
|
|
// No need to gc->next->prev = prev because it is single linked.
|
|
prev->_gc_next = gc->_gc_next;
|
|
|
|
// We can't use gc_list_append() here because we use
|
|
// NEXT_MASK_UNREACHABLE here.
|
|
PyGC_Head *last = GC_PREV(unreachable);
|
|
// NOTE: Since all objects in unreachable set has
|
|
// NEXT_MASK_UNREACHABLE flag, we set it unconditionally.
|
|
// But this may pollute the unreachable list head's 'next' pointer
|
|
// too. That's semantically senseless but expedient here - the
|
|
// damage is repaired when this fumction ends.
|
|
last->_gc_next = (NEXT_MASK_UNREACHABLE | (uintptr_t)gc);
|
|
_PyGCHead_SET_PREV(gc, last);
|
|
gc->_gc_next = (NEXT_MASK_UNREACHABLE | (uintptr_t)unreachable);
|
|
unreachable->_gc_prev = (uintptr_t)gc;
|
|
}
|
|
gc = (PyGC_Head*)prev->_gc_next;
|
|
}
|
|
// young->_gc_prev must be last element remained in the list.
|
|
young->_gc_prev = (uintptr_t)prev;
|
|
// don't let the pollution of the list head's next pointer leak
|
|
unreachable->_gc_next &= ~NEXT_MASK_UNREACHABLE;
|
|
}
|
|
|
|
static void
|
|
untrack_tuples(PyGC_Head *head)
|
|
{
|
|
PyGC_Head *next, *gc = GC_NEXT(head);
|
|
while (gc != head) {
|
|
PyObject *op = FROM_GC(gc);
|
|
next = GC_NEXT(gc);
|
|
if (PyTuple_CheckExact(op)) {
|
|
_PyTuple_MaybeUntrack(op);
|
|
}
|
|
gc = next;
|
|
}
|
|
}
|
|
|
|
/* Try to untrack all currently tracked dictionaries */
|
|
static void
|
|
untrack_dicts(PyGC_Head *head)
|
|
{
|
|
PyGC_Head *next, *gc = GC_NEXT(head);
|
|
while (gc != head) {
|
|
PyObject *op = FROM_GC(gc);
|
|
next = GC_NEXT(gc);
|
|
if (PyDict_CheckExact(op)) {
|
|
_PyDict_MaybeUntrack(op);
|
|
}
|
|
gc = next;
|
|
}
|
|
}
|
|
|
|
/* Return true if object has a pre-PEP 442 finalization method. */
|
|
static int
|
|
has_legacy_finalizer(PyObject *op)
|
|
{
|
|
return op->ob_type->tp_del != NULL;
|
|
}
|
|
|
|
/* Move the objects in unreachable with tp_del slots into `finalizers`.
|
|
*
|
|
* This function also removes NEXT_MASK_UNREACHABLE flag
|
|
* from _gc_next in unreachable.
|
|
*/
|
|
static void
|
|
move_legacy_finalizers(PyGC_Head *unreachable, PyGC_Head *finalizers)
|
|
{
|
|
PyGC_Head *gc, *next;
|
|
assert((unreachable->_gc_next & NEXT_MASK_UNREACHABLE) == 0);
|
|
|
|
/* March over unreachable. Move objects with finalizers into
|
|
* `finalizers`.
|
|
*/
|
|
for (gc = GC_NEXT(unreachable); gc != unreachable; gc = next) {
|
|
PyObject *op = FROM_GC(gc);
|
|
|
|
_PyObject_ASSERT(op, gc->_gc_next & NEXT_MASK_UNREACHABLE);
|
|
gc->_gc_next &= ~NEXT_MASK_UNREACHABLE;
|
|
next = (PyGC_Head*)gc->_gc_next;
|
|
|
|
if (has_legacy_finalizer(op)) {
|
|
gc_clear_collecting(gc);
|
|
gc_list_move(gc, finalizers);
|
|
}
|
|
}
|
|
}
|
|
|
|
static inline void
|
|
clear_unreachable_mask(PyGC_Head *unreachable)
|
|
{
|
|
/* Check that the list head does not have the unreachable bit set */
|
|
assert(((uintptr_t)unreachable & NEXT_MASK_UNREACHABLE) == 0);
|
|
|
|
PyGC_Head *gc, *next;
|
|
assert((unreachable->_gc_next & NEXT_MASK_UNREACHABLE) == 0);
|
|
for (gc = GC_NEXT(unreachable); gc != unreachable; gc = next) {
|
|
_PyObject_ASSERT((PyObject*)FROM_GC(gc), gc->_gc_next & NEXT_MASK_UNREACHABLE);
|
|
gc->_gc_next &= ~NEXT_MASK_UNREACHABLE;
|
|
next = (PyGC_Head*)gc->_gc_next;
|
|
}
|
|
validate_list(unreachable, collecting_set_unreachable_clear);
|
|
}
|
|
|
|
/* A traversal callback for move_legacy_finalizer_reachable. */
|
|
static int
|
|
visit_move(PyObject *op, PyGC_Head *tolist)
|
|
{
|
|
if (PyObject_IS_GC(op)) {
|
|
PyGC_Head *gc = AS_GC(op);
|
|
if (gc_is_collecting(gc)) {
|
|
gc_list_move(gc, tolist);
|
|
gc_clear_collecting(gc);
|
|
}
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
/* Move objects that are reachable from finalizers, from the unreachable set
|
|
* into finalizers set.
|
|
*/
|
|
static void
|
|
move_legacy_finalizer_reachable(PyGC_Head *finalizers)
|
|
{
|
|
traverseproc traverse;
|
|
PyGC_Head *gc = GC_NEXT(finalizers);
|
|
for (; gc != finalizers; gc = GC_NEXT(gc)) {
|
|
/* Note that the finalizers list may grow during this. */
|
|
traverse = Py_TYPE(FROM_GC(gc))->tp_traverse;
|
|
(void) traverse(FROM_GC(gc),
|
|
(visitproc)visit_move,
|
|
(void *)finalizers);
|
|
}
|
|
}
|
|
|
|
/* Clear all weakrefs to unreachable objects, and if such a weakref has a
|
|
* callback, invoke it if necessary. Note that it's possible for such
|
|
* weakrefs to be outside the unreachable set -- indeed, those are precisely
|
|
* the weakrefs whose callbacks must be invoked. See gc_weakref.txt for
|
|
* overview & some details. Some weakrefs with callbacks may be reclaimed
|
|
* directly by this routine; the number reclaimed is the return value. Other
|
|
* weakrefs with callbacks may be moved into the `old` generation. Objects
|
|
* moved into `old` have gc_refs set to GC_REACHABLE; the objects remaining in
|
|
* unreachable are left at GC_TENTATIVELY_UNREACHABLE. When this returns,
|
|
* no object in `unreachable` is weakly referenced anymore.
|
|
*/
|
|
static int
|
|
handle_weakrefs(PyGC_Head *unreachable, PyGC_Head *old)
|
|
{
|
|
PyGC_Head *gc;
|
|
PyObject *op; /* generally FROM_GC(gc) */
|
|
PyWeakReference *wr; /* generally a cast of op */
|
|
PyGC_Head wrcb_to_call; /* weakrefs with callbacks to call */
|
|
PyGC_Head *next;
|
|
int num_freed = 0;
|
|
|
|
gc_list_init(&wrcb_to_call);
|
|
|
|
/* Clear all weakrefs to the objects in unreachable. If such a weakref
|
|
* also has a callback, move it into `wrcb_to_call` if the callback
|
|
* needs to be invoked. Note that we cannot invoke any callbacks until
|
|
* all weakrefs to unreachable objects are cleared, lest the callback
|
|
* resurrect an unreachable object via a still-active weakref. We
|
|
* make another pass over wrcb_to_call, invoking callbacks, after this
|
|
* pass completes.
|
|
*/
|
|
for (gc = GC_NEXT(unreachable); gc != unreachable; gc = next) {
|
|
PyWeakReference **wrlist;
|
|
|
|
op = FROM_GC(gc);
|
|
next = GC_NEXT(gc);
|
|
|
|
if (PyWeakref_Check(op)) {
|
|
/* A weakref inside the unreachable set must be cleared. If we
|
|
* allow its callback to execute inside delete_garbage(), it
|
|
* could expose objects that have tp_clear already called on
|
|
* them. Or, it could resurrect unreachable objects. One way
|
|
* this can happen is if some container objects do not implement
|
|
* tp_traverse. Then, wr_object can be outside the unreachable
|
|
* set but can be deallocated as a result of breaking the
|
|
* reference cycle. If we don't clear the weakref, the callback
|
|
* will run and potentially cause a crash. See bpo-38006 for
|
|
* one example.
|
|
*/
|
|
_PyWeakref_ClearRef((PyWeakReference *)op);
|
|
}
|
|
|
|
if (! PyType_SUPPORTS_WEAKREFS(Py_TYPE(op)))
|
|
continue;
|
|
|
|
/* It supports weakrefs. Does it have any? */
|
|
wrlist = (PyWeakReference **)
|
|
PyObject_GET_WEAKREFS_LISTPTR(op);
|
|
|
|
/* `op` may have some weakrefs. March over the list, clear
|
|
* all the weakrefs, and move the weakrefs with callbacks
|
|
* that must be called into wrcb_to_call.
|
|
*/
|
|
for (wr = *wrlist; wr != NULL; wr = *wrlist) {
|
|
PyGC_Head *wrasgc; /* AS_GC(wr) */
|
|
|
|
/* _PyWeakref_ClearRef clears the weakref but leaves
|
|
* the callback pointer intact. Obscure: it also
|
|
* changes *wrlist.
|
|
*/
|
|
_PyObject_ASSERT((PyObject *)wr, wr->wr_object == op);
|
|
_PyWeakref_ClearRef(wr);
|
|
_PyObject_ASSERT((PyObject *)wr, wr->wr_object == Py_None);
|
|
if (wr->wr_callback == NULL) {
|
|
/* no callback */
|
|
continue;
|
|
}
|
|
|
|
/* Headache time. `op` is going away, and is weakly referenced by
|
|
* `wr`, which has a callback. Should the callback be invoked? If wr
|
|
* is also trash, no:
|
|
*
|
|
* 1. There's no need to call it. The object and the weakref are
|
|
* both going away, so it's legitimate to pretend the weakref is
|
|
* going away first. The user has to ensure a weakref outlives its
|
|
* referent if they want a guarantee that the wr callback will get
|
|
* invoked.
|
|
*
|
|
* 2. It may be catastrophic to call it. If the callback is also in
|
|
* cyclic trash (CT), then although the CT is unreachable from
|
|
* outside the current generation, CT may be reachable from the
|
|
* callback. Then the callback could resurrect insane objects.
|
|
*
|
|
* Since the callback is never needed and may be unsafe in this case,
|
|
* wr is simply left in the unreachable set. Note that because we
|
|
* already called _PyWeakref_ClearRef(wr), its callback will never
|
|
* trigger.
|
|
*
|
|
* OTOH, if wr isn't part of CT, we should invoke the callback: the
|
|
* weakref outlived the trash. Note that since wr isn't CT in this
|
|
* case, its callback can't be CT either -- wr acted as an external
|
|
* root to this generation, and therefore its callback did too. So
|
|
* nothing in CT is reachable from the callback either, so it's hard
|
|
* to imagine how calling it later could create a problem for us. wr
|
|
* is moved to wrcb_to_call in this case.
|
|
*/
|
|
if (gc_is_collecting(AS_GC(wr))) {
|
|
/* it should already have been cleared above */
|
|
assert(wr->wr_object == Py_None);
|
|
continue;
|
|
}
|
|
|
|
/* Create a new reference so that wr can't go away
|
|
* before we can process it again.
|
|
*/
|
|
Py_INCREF(wr);
|
|
|
|
/* Move wr to wrcb_to_call, for the next pass. */
|
|
wrasgc = AS_GC(wr);
|
|
assert(wrasgc != next); /* wrasgc is reachable, but
|
|
next isn't, so they can't
|
|
be the same */
|
|
gc_list_move(wrasgc, &wrcb_to_call);
|
|
}
|
|
}
|
|
|
|
/* Invoke the callbacks we decided to honor. It's safe to invoke them
|
|
* because they can't reference unreachable objects.
|
|
*/
|
|
while (! gc_list_is_empty(&wrcb_to_call)) {
|
|
PyObject *temp;
|
|
PyObject *callback;
|
|
|
|
gc = (PyGC_Head*)wrcb_to_call._gc_next;
|
|
op = FROM_GC(gc);
|
|
_PyObject_ASSERT(op, PyWeakref_Check(op));
|
|
wr = (PyWeakReference *)op;
|
|
callback = wr->wr_callback;
|
|
_PyObject_ASSERT(op, callback != NULL);
|
|
|
|
/* copy-paste of weakrefobject.c's handle_callback() */
|
|
temp = _PyObject_CallOneArg(callback, (PyObject *)wr);
|
|
if (temp == NULL)
|
|
PyErr_WriteUnraisable(callback);
|
|
else
|
|
Py_DECREF(temp);
|
|
|
|
/* Give up the reference we created in the first pass. When
|
|
* op's refcount hits 0 (which it may or may not do right now),
|
|
* op's tp_dealloc will decref op->wr_callback too. Note
|
|
* that the refcount probably will hit 0 now, and because this
|
|
* weakref was reachable to begin with, gc didn't already
|
|
* add it to its count of freed objects. Example: a reachable
|
|
* weak value dict maps some key to this reachable weakref.
|
|
* The callback removes this key->weakref mapping from the
|
|
* dict, leaving no other references to the weakref (excepting
|
|
* ours).
|
|
*/
|
|
Py_DECREF(op);
|
|
if (wrcb_to_call._gc_next == (uintptr_t)gc) {
|
|
/* object is still alive -- move it */
|
|
gc_list_move(gc, old);
|
|
}
|
|
else {
|
|
++num_freed;
|
|
}
|
|
}
|
|
|
|
return num_freed;
|
|
}
|
|
|
|
static void
|
|
debug_cycle(const char *msg, PyObject *op)
|
|
{
|
|
PySys_FormatStderr("gc: %s <%s %p>\n",
|
|
msg, Py_TYPE(op)->tp_name, op);
|
|
}
|
|
|
|
/* Handle uncollectable garbage (cycles with tp_del slots, and stuff reachable
|
|
* only from such cycles).
|
|
* If DEBUG_SAVEALL, all objects in finalizers are appended to the module
|
|
* garbage list (a Python list), else only the objects in finalizers with
|
|
* __del__ methods are appended to garbage. All objects in finalizers are
|
|
* merged into the old list regardless.
|
|
*/
|
|
static void
|
|
handle_legacy_finalizers(PyThreadState *tstate,
|
|
GCState *gcstate,
|
|
PyGC_Head *finalizers, PyGC_Head *old)
|
|
{
|
|
assert(!_PyErr_Occurred(tstate));
|
|
assert(gcstate->garbage != NULL);
|
|
|
|
PyGC_Head *gc = GC_NEXT(finalizers);
|
|
for (; gc != finalizers; gc = GC_NEXT(gc)) {
|
|
PyObject *op = FROM_GC(gc);
|
|
|
|
if ((gcstate->debug & DEBUG_SAVEALL) || has_legacy_finalizer(op)) {
|
|
if (PyList_Append(gcstate->garbage, op) < 0) {
|
|
_PyErr_Clear(tstate);
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
gc_list_merge(finalizers, old);
|
|
}
|
|
|
|
/* Run first-time finalizers (if any) on all the objects in collectable.
|
|
* Note that this may remove some (or even all) of the objects from the
|
|
* list, due to refcounts falling to 0.
|
|
*/
|
|
static void
|
|
finalize_garbage(PyThreadState *tstate, PyGC_Head *collectable)
|
|
{
|
|
destructor finalize;
|
|
PyGC_Head seen;
|
|
|
|
/* While we're going through the loop, `finalize(op)` may cause op, or
|
|
* other objects, to be reclaimed via refcounts falling to zero. So
|
|
* there's little we can rely on about the structure of the input
|
|
* `collectable` list across iterations. For safety, we always take the
|
|
* first object in that list and move it to a temporary `seen` list.
|
|
* If objects vanish from the `collectable` and `seen` lists we don't
|
|
* care.
|
|
*/
|
|
gc_list_init(&seen);
|
|
|
|
while (!gc_list_is_empty(collectable)) {
|
|
PyGC_Head *gc = GC_NEXT(collectable);
|
|
PyObject *op = FROM_GC(gc);
|
|
gc_list_move(gc, &seen);
|
|
if (!_PyGCHead_FINALIZED(gc) &&
|
|
(finalize = Py_TYPE(op)->tp_finalize) != NULL) {
|
|
_PyGCHead_SET_FINALIZED(gc);
|
|
Py_INCREF(op);
|
|
finalize(op);
|
|
assert(!_PyErr_Occurred(tstate));
|
|
Py_DECREF(op);
|
|
}
|
|
}
|
|
gc_list_merge(&seen, collectable);
|
|
}
|
|
|
|
/* Break reference cycles by clearing the containers involved. This is
|
|
* tricky business as the lists can be changing and we don't know which
|
|
* objects may be freed. It is possible I screwed something up here.
|
|
*/
|
|
static void
|
|
delete_garbage(PyThreadState *tstate, GCState *gcstate,
|
|
PyGC_Head *collectable, PyGC_Head *old)
|
|
{
|
|
assert(!_PyErr_Occurred(tstate));
|
|
|
|
while (!gc_list_is_empty(collectable)) {
|
|
PyGC_Head *gc = GC_NEXT(collectable);
|
|
PyObject *op = FROM_GC(gc);
|
|
|
|
_PyObject_ASSERT_WITH_MSG(op, Py_REFCNT(op) > 0,
|
|
"refcount is too small");
|
|
|
|
if (gcstate->debug & DEBUG_SAVEALL) {
|
|
assert(gcstate->garbage != NULL);
|
|
if (PyList_Append(gcstate->garbage, op) < 0) {
|
|
_PyErr_Clear(tstate);
|
|
}
|
|
}
|
|
else {
|
|
inquiry clear;
|
|
if ((clear = Py_TYPE(op)->tp_clear) != NULL) {
|
|
Py_INCREF(op);
|
|
(void) clear(op);
|
|
if (_PyErr_Occurred(tstate)) {
|
|
_PyErr_WriteUnraisableMsg("in tp_clear of",
|
|
(PyObject*)Py_TYPE(op));
|
|
}
|
|
Py_DECREF(op);
|
|
}
|
|
}
|
|
if (GC_NEXT(collectable) == gc) {
|
|
/* object is still alive, move it, it may die later */
|
|
gc_clear_collecting(gc);
|
|
gc_list_move(gc, old);
|
|
}
|
|
}
|
|
}
|
|
|
|
/* Clear all free lists
|
|
* All free lists are cleared during the collection of the highest generation.
|
|
* Allocated items in the free list may keep a pymalloc arena occupied.
|
|
* Clearing the free lists may give back memory to the OS earlier.
|
|
*/
|
|
static void
|
|
clear_freelists(void)
|
|
{
|
|
(void)PyFrame_ClearFreeList();
|
|
(void)PyTuple_ClearFreeList();
|
|
(void)PyFloat_ClearFreeList();
|
|
(void)PyList_ClearFreeList();
|
|
(void)PyDict_ClearFreeList();
|
|
(void)PySet_ClearFreeList();
|
|
(void)PyAsyncGen_ClearFreeLists();
|
|
(void)PyContext_ClearFreeList();
|
|
}
|
|
|
|
// Show stats for objects in each gennerations.
|
|
static void
|
|
show_stats_each_generations(GCState *gcstate)
|
|
{
|
|
char buf[100];
|
|
size_t pos = 0;
|
|
|
|
for (int i = 0; i < NUM_GENERATIONS && pos < sizeof(buf); i++) {
|
|
pos += PyOS_snprintf(buf+pos, sizeof(buf)-pos,
|
|
" %"PY_FORMAT_SIZE_T"d",
|
|
gc_list_size(GEN_HEAD(gcstate, i)));
|
|
}
|
|
|
|
PySys_FormatStderr(
|
|
"gc: objects in each generation:%s\n"
|
|
"gc: objects in permanent generation: %zd\n",
|
|
buf, gc_list_size(&gcstate->permanent_generation.head));
|
|
}
|
|
|
|
/* Deduce wich objects among "base" are unreachable from outside the list
|
|
and move them to 'unreachable'. The process consist in the following steps:
|
|
|
|
1. Copy all reference counts to a different field (gc_prev is used to hold
|
|
this copy to save memory).
|
|
2. Traverse all objects in "base" and visit all referred objects using
|
|
"tp_traverse" and for every visited object, substract 1 to the reference
|
|
count (the one that we copied in the previous step). After this step, all
|
|
objects that can be reached directly from outside must have strictly positive
|
|
reference count, while all unreachable objects must have a count of exactly 0.
|
|
3. Indentify all unreachable objects (the ones with 0 reference count) and move
|
|
them to the "unreachable" list. This step also needs to move back to "base" all
|
|
objects that were initially marked as unreachable but are referred transitively
|
|
by the reachable objects (the ones with strictly positive reference count).
|
|
|
|
Contracts:
|
|
|
|
* The "base" has to be a valid list with no mask set.
|
|
|
|
* The "unreachable" list must be uninitialized (this function calls
|
|
gc_list_init over 'unreachable').
|
|
|
|
IMPORTANT: This function leaves 'unreachable' with the NEXT_MASK_UNREACHABLE
|
|
flag set but it does not clear it to skip unnecessary iteration. Before the
|
|
flag is cleared (for example, by using 'clear_unreachable_mask' function or
|
|
by a call to 'move_legacy_finalizers'), the 'unreachable' list is not a normal
|
|
list and we can not use most gc_list_* functions for it. */
|
|
static inline void
|
|
deduce_unreachable(PyGC_Head *base, PyGC_Head *unreachable) {
|
|
validate_list(base, collecting_clear_unreachable_clear);
|
|
/* Using ob_refcnt and gc_refs, calculate which objects in the
|
|
* container set are reachable from outside the set (i.e., have a
|
|
* refcount greater than 0 when all the references within the
|
|
* set are taken into account).
|
|
*/
|
|
update_refs(base); // gc_prev is used for gc_refs
|
|
subtract_refs(base);
|
|
|
|
/* Leave everything reachable from outside base in base, and move
|
|
* everything else (in base) to unreachable.
|
|
* NOTE: This used to move the reachable objects into a reachable
|
|
* set instead. But most things usually turn out to be reachable,
|
|
* so it's more efficient to move the unreachable things. See note
|
|
^ [REACHABLE OR UNREACHABLE?] at the file end.
|
|
*/
|
|
gc_list_init(unreachable);
|
|
move_unreachable(base, unreachable); // gc_prev is pointer again
|
|
validate_list(base, collecting_clear_unreachable_clear);
|
|
validate_list(unreachable, collecting_set_unreachable_set);
|
|
}
|
|
|
|
/* Handle objects that may have resurrected after a call to 'finalize_garbage', moving
|
|
them to 'old_generation' and placing the rest on 'still_unreachable'.
|
|
|
|
Contracts:
|
|
* After this function 'unreachable' must not be used anymore and 'still_unreachable'
|
|
will contain the objects that did not resurrect.
|
|
|
|
* The "still_unreachable" list must be uninitialized (this function calls
|
|
gc_list_init over 'still_unreachable').
|
|
|
|
IMPORTANT: After a call to this function, the 'still_unreachable' set will have the
|
|
PREV_MARK_COLLECTING set, but the objects in this set are going to be removed so
|
|
we can skip the expense of clearing the flag to avoid extra iteration. */
|
|
static inline void
|
|
handle_resurrected_objects(PyGC_Head *unreachable, PyGC_Head* still_unreachable,
|
|
PyGC_Head *old_generation)
|
|
{
|
|
// Remove the PREV_MASK_COLLECTING from unreachable
|
|
// to prepare it for a new call to 'deduce_unreachable'
|
|
gc_list_clear_collecting(unreachable);
|
|
|
|
// After the call to deduce_unreachable, the 'still_unreachable' set will
|
|
// have the PREV_MARK_COLLECTING set, but the objects are going to be
|
|
// removed so we can skip the expense of clearing the flag.
|
|
PyGC_Head* resurrected = unreachable;
|
|
deduce_unreachable(resurrected, still_unreachable);
|
|
clear_unreachable_mask(still_unreachable);
|
|
|
|
// Move the resurrected objects to the old generation for future collection.
|
|
gc_list_merge(resurrected, old_generation);
|
|
}
|
|
|
|
/* This is the main function. Read this to understand how the
|
|
* collection process works. */
|
|
static Py_ssize_t
|
|
collect(PyThreadState *tstate, int generation,
|
|
Py_ssize_t *n_collected, Py_ssize_t *n_uncollectable, int nofail)
|
|
{
|
|
int i;
|
|
Py_ssize_t m = 0; /* # objects collected */
|
|
Py_ssize_t n = 0; /* # unreachable objects that couldn't be collected */
|
|
PyGC_Head *young; /* the generation we are examining */
|
|
PyGC_Head *old; /* next older generation */
|
|
PyGC_Head unreachable; /* non-problematic unreachable trash */
|
|
PyGC_Head finalizers; /* objects with, & reachable from, __del__ */
|
|
PyGC_Head *gc;
|
|
_PyTime_t t1 = 0; /* initialize to prevent a compiler warning */
|
|
GCState *gcstate = &tstate->interp->gc;
|
|
|
|
if (gcstate->debug & DEBUG_STATS) {
|
|
PySys_WriteStderr("gc: collecting generation %d...\n", generation);
|
|
show_stats_each_generations(gcstate);
|
|
t1 = _PyTime_GetMonotonicClock();
|
|
}
|
|
|
|
if (PyDTrace_GC_START_ENABLED())
|
|
PyDTrace_GC_START(generation);
|
|
|
|
/* update collection and allocation counters */
|
|
if (generation+1 < NUM_GENERATIONS)
|
|
gcstate->generations[generation+1].count += 1;
|
|
for (i = 0; i <= generation; i++)
|
|
gcstate->generations[i].count = 0;
|
|
|
|
/* merge younger generations with one we are currently collecting */
|
|
for (i = 0; i < generation; i++) {
|
|
gc_list_merge(GEN_HEAD(gcstate, i), GEN_HEAD(gcstate, generation));
|
|
}
|
|
|
|
/* handy references */
|
|
young = GEN_HEAD(gcstate, generation);
|
|
if (generation < NUM_GENERATIONS-1)
|
|
old = GEN_HEAD(gcstate, generation+1);
|
|
else
|
|
old = young;
|
|
validate_list(old, collecting_clear_unreachable_clear);
|
|
|
|
deduce_unreachable(young, &unreachable);
|
|
|
|
untrack_tuples(young);
|
|
/* Move reachable objects to next generation. */
|
|
if (young != old) {
|
|
if (generation == NUM_GENERATIONS - 2) {
|
|
gcstate->long_lived_pending += gc_list_size(young);
|
|
}
|
|
gc_list_merge(young, old);
|
|
}
|
|
else {
|
|
/* We only untrack dicts in full collections, to avoid quadratic
|
|
dict build-up. See issue #14775. */
|
|
untrack_dicts(young);
|
|
gcstate->long_lived_pending = 0;
|
|
gcstate->long_lived_total = gc_list_size(young);
|
|
}
|
|
|
|
/* All objects in unreachable are trash, but objects reachable from
|
|
* legacy finalizers (e.g. tp_del) can't safely be deleted.
|
|
*/
|
|
gc_list_init(&finalizers);
|
|
// NEXT_MASK_UNREACHABLE is cleared here.
|
|
// After move_legacy_finalizers(), unreachable is normal list.
|
|
move_legacy_finalizers(&unreachable, &finalizers);
|
|
/* finalizers contains the unreachable objects with a legacy finalizer;
|
|
* unreachable objects reachable *from* those are also uncollectable,
|
|
* and we move those into the finalizers list too.
|
|
*/
|
|
move_legacy_finalizer_reachable(&finalizers);
|
|
|
|
validate_list(&finalizers, collecting_clear_unreachable_clear);
|
|
validate_list(&unreachable, collecting_set_unreachable_clear);
|
|
|
|
/* Print debugging information. */
|
|
if (gcstate->debug & DEBUG_COLLECTABLE) {
|
|
for (gc = GC_NEXT(&unreachable); gc != &unreachable; gc = GC_NEXT(gc)) {
|
|
debug_cycle("collectable", FROM_GC(gc));
|
|
}
|
|
}
|
|
|
|
/* Clear weakrefs and invoke callbacks as necessary. */
|
|
m += handle_weakrefs(&unreachable, old);
|
|
|
|
validate_list(old, collecting_clear_unreachable_clear);
|
|
validate_list(&unreachable, collecting_set_unreachable_clear);
|
|
|
|
/* Call tp_finalize on objects which have one. */
|
|
finalize_garbage(tstate, &unreachable);
|
|
|
|
/* Handle any objects that may have resurrected after the call
|
|
* to 'finalize_garbage' and continue the collection with the
|
|
* objects that are still unreachable */
|
|
PyGC_Head final_unreachable;
|
|
handle_resurrected_objects(&unreachable, &final_unreachable, old);
|
|
|
|
/* Call tp_clear on objects in the final_unreachable set. This will cause
|
|
* the reference cycles to be broken. It may also cause some objects
|
|
* in finalizers to be freed.
|
|
*/
|
|
m += gc_list_size(&final_unreachable);
|
|
delete_garbage(tstate, gcstate, &final_unreachable, old);
|
|
|
|
/* Collect statistics on uncollectable objects found and print
|
|
* debugging information. */
|
|
for (gc = GC_NEXT(&finalizers); gc != &finalizers; gc = GC_NEXT(gc)) {
|
|
n++;
|
|
if (gcstate->debug & DEBUG_UNCOLLECTABLE)
|
|
debug_cycle("uncollectable", FROM_GC(gc));
|
|
}
|
|
if (gcstate->debug & DEBUG_STATS) {
|
|
double d = _PyTime_AsSecondsDouble(_PyTime_GetMonotonicClock() - t1);
|
|
PySys_WriteStderr(
|
|
"gc: done, %" PY_FORMAT_SIZE_T "d unreachable, "
|
|
"%" PY_FORMAT_SIZE_T "d uncollectable, %.4fs elapsed\n",
|
|
n+m, n, d);
|
|
}
|
|
|
|
/* Append instances in the uncollectable set to a Python
|
|
* reachable list of garbage. The programmer has to deal with
|
|
* this if they insist on creating this type of structure.
|
|
*/
|
|
handle_legacy_finalizers(tstate, gcstate, &finalizers, old);
|
|
validate_list(old, collecting_clear_unreachable_clear);
|
|
|
|
/* Clear free list only during the collection of the highest
|
|
* generation */
|
|
if (generation == NUM_GENERATIONS-1) {
|
|
clear_freelists();
|
|
}
|
|
|
|
if (_PyErr_Occurred(tstate)) {
|
|
if (nofail) {
|
|
_PyErr_Clear(tstate);
|
|
}
|
|
else {
|
|
if (gc_str == NULL)
|
|
gc_str = PyUnicode_FromString("garbage collection");
|
|
PyErr_WriteUnraisable(gc_str);
|
|
Py_FatalError("unexpected exception during garbage collection");
|
|
}
|
|
}
|
|
|
|
/* Update stats */
|
|
if (n_collected) {
|
|
*n_collected = m;
|
|
}
|
|
if (n_uncollectable) {
|
|
*n_uncollectable = n;
|
|
}
|
|
|
|
struct gc_generation_stats *stats = &gcstate->generation_stats[generation];
|
|
stats->collections++;
|
|
stats->collected += m;
|
|
stats->uncollectable += n;
|
|
|
|
if (PyDTrace_GC_DONE_ENABLED()) {
|
|
PyDTrace_GC_DONE(n + m);
|
|
}
|
|
|
|
assert(!_PyErr_Occurred(tstate));
|
|
return n + m;
|
|
}
|
|
|
|
/* Invoke progress callbacks to notify clients that garbage collection
|
|
* is starting or stopping
|
|
*/
|
|
static void
|
|
invoke_gc_callback(PyThreadState *tstate, const char *phase,
|
|
int generation, Py_ssize_t collected,
|
|
Py_ssize_t uncollectable)
|
|
{
|
|
assert(!_PyErr_Occurred(tstate));
|
|
|
|
/* we may get called very early */
|
|
GCState *gcstate = &tstate->interp->gc;
|
|
if (gcstate->callbacks == NULL) {
|
|
return;
|
|
}
|
|
|
|
/* The local variable cannot be rebound, check it for sanity */
|
|
assert(PyList_CheckExact(gcstate->callbacks));
|
|
PyObject *info = NULL;
|
|
if (PyList_GET_SIZE(gcstate->callbacks) != 0) {
|
|
info = Py_BuildValue("{sisnsn}",
|
|
"generation", generation,
|
|
"collected", collected,
|
|
"uncollectable", uncollectable);
|
|
if (info == NULL) {
|
|
PyErr_WriteUnraisable(NULL);
|
|
return;
|
|
}
|
|
}
|
|
for (Py_ssize_t i=0; i<PyList_GET_SIZE(gcstate->callbacks); i++) {
|
|
PyObject *r, *cb = PyList_GET_ITEM(gcstate->callbacks, i);
|
|
Py_INCREF(cb); /* make sure cb doesn't go away */
|
|
r = PyObject_CallFunction(cb, "sO", phase, info);
|
|
if (r == NULL) {
|
|
PyErr_WriteUnraisable(cb);
|
|
}
|
|
else {
|
|
Py_DECREF(r);
|
|
}
|
|
Py_DECREF(cb);
|
|
}
|
|
Py_XDECREF(info);
|
|
assert(!_PyErr_Occurred(tstate));
|
|
}
|
|
|
|
/* Perform garbage collection of a generation and invoke
|
|
* progress callbacks.
|
|
*/
|
|
static Py_ssize_t
|
|
collect_with_callback(PyThreadState *tstate, int generation)
|
|
{
|
|
assert(!_PyErr_Occurred(tstate));
|
|
Py_ssize_t result, collected, uncollectable;
|
|
invoke_gc_callback(tstate, "start", generation, 0, 0);
|
|
result = collect(tstate, generation, &collected, &uncollectable, 0);
|
|
invoke_gc_callback(tstate, "stop", generation, collected, uncollectable);
|
|
assert(!_PyErr_Occurred(tstate));
|
|
return result;
|
|
}
|
|
|
|
static Py_ssize_t
|
|
collect_generations(PyThreadState *tstate)
|
|
{
|
|
GCState *gcstate = &tstate->interp->gc;
|
|
/* Find the oldest generation (highest numbered) where the count
|
|
* exceeds the threshold. Objects in the that generation and
|
|
* generations younger than it will be collected. */
|
|
Py_ssize_t n = 0;
|
|
for (int i = NUM_GENERATIONS-1; i >= 0; i--) {
|
|
if (gcstate->generations[i].count > gcstate->generations[i].threshold) {
|
|
/* Avoid quadratic performance degradation in number
|
|
of tracked objects (see also issue #4074):
|
|
|
|
To limit the cost of garbage collection, there are two strategies;
|
|
- make each collection faster, e.g. by scanning fewer objects
|
|
- do less collections
|
|
This heuristic is about the latter strategy.
|
|
|
|
In addition to the various configurable thresholds, we only trigger a
|
|
full collection if the ratio
|
|
|
|
long_lived_pending / long_lived_total
|
|
|
|
is above a given value (hardwired to 25%).
|
|
|
|
The reason is that, while "non-full" collections (i.e., collections of
|
|
the young and middle generations) will always examine roughly the same
|
|
number of objects -- determined by the aforementioned thresholds --,
|
|
the cost of a full collection is proportional to the total number of
|
|
long-lived objects, which is virtually unbounded.
|
|
|
|
Indeed, it has been remarked that doing a full collection every
|
|
<constant number> of object creations entails a dramatic performance
|
|
degradation in workloads which consist in creating and storing lots of
|
|
long-lived objects (e.g. building a large list of GC-tracked objects would
|
|
show quadratic performance, instead of linear as expected: see issue #4074).
|
|
|
|
Using the above ratio, instead, yields amortized linear performance in
|
|
the total number of objects (the effect of which can be summarized
|
|
thusly: "each full garbage collection is more and more costly as the
|
|
number of objects grows, but we do fewer and fewer of them").
|
|
|
|
This heuristic was suggested by Martin von Löwis on python-dev in
|
|
June 2008. His original analysis and proposal can be found at:
|
|
http://mail.python.org/pipermail/python-dev/2008-June/080579.html
|
|
*/
|
|
if (i == NUM_GENERATIONS - 1
|
|
&& gcstate->long_lived_pending < gcstate->long_lived_total / 4)
|
|
continue;
|
|
n = collect_with_callback(tstate, i);
|
|
break;
|
|
}
|
|
}
|
|
return n;
|
|
}
|
|
|
|
#include "clinic/gcmodule.c.h"
|
|
|
|
/*[clinic input]
|
|
gc.enable
|
|
|
|
Enable automatic garbage collection.
|
|
[clinic start generated code]*/
|
|
|
|
static PyObject *
|
|
gc_enable_impl(PyObject *module)
|
|
/*[clinic end generated code: output=45a427e9dce9155c input=81ac4940ca579707]*/
|
|
{
|
|
PyThreadState *tstate = _PyThreadState_GET();
|
|
GCState *gcstate = &tstate->interp->gc;
|
|
gcstate->enabled = 1;
|
|
Py_RETURN_NONE;
|
|
}
|
|
|
|
/*[clinic input]
|
|
gc.disable
|
|
|
|
Disable automatic garbage collection.
|
|
[clinic start generated code]*/
|
|
|
|
static PyObject *
|
|
gc_disable_impl(PyObject *module)
|
|
/*[clinic end generated code: output=97d1030f7aa9d279 input=8c2e5a14e800d83b]*/
|
|
{
|
|
PyThreadState *tstate = _PyThreadState_GET();
|
|
GCState *gcstate = &tstate->interp->gc;
|
|
gcstate->enabled = 0;
|
|
Py_RETURN_NONE;
|
|
}
|
|
|
|
/*[clinic input]
|
|
gc.isenabled -> bool
|
|
|
|
Returns true if automatic garbage collection is enabled.
|
|
[clinic start generated code]*/
|
|
|
|
static int
|
|
gc_isenabled_impl(PyObject *module)
|
|
/*[clinic end generated code: output=1874298331c49130 input=30005e0422373b31]*/
|
|
{
|
|
PyThreadState *tstate = _PyThreadState_GET();
|
|
GCState *gcstate = &tstate->interp->gc;
|
|
return gcstate->enabled;
|
|
}
|
|
|
|
/*[clinic input]
|
|
gc.collect -> Py_ssize_t
|
|
|
|
generation: int(c_default="NUM_GENERATIONS - 1") = 2
|
|
|
|
Run the garbage collector.
|
|
|
|
With no arguments, run a full collection. The optional argument
|
|
may be an integer specifying which generation to collect. A ValueError
|
|
is raised if the generation number is invalid.
|
|
|
|
The number of unreachable objects is returned.
|
|
[clinic start generated code]*/
|
|
|
|
static Py_ssize_t
|
|
gc_collect_impl(PyObject *module, int generation)
|
|
/*[clinic end generated code: output=b697e633043233c7 input=40720128b682d879]*/
|
|
{
|
|
PyThreadState *tstate = _PyThreadState_GET();
|
|
|
|
if (generation < 0 || generation >= NUM_GENERATIONS) {
|
|
_PyErr_SetString(tstate, PyExc_ValueError, "invalid generation");
|
|
return -1;
|
|
}
|
|
|
|
GCState *gcstate = &tstate->interp->gc;
|
|
Py_ssize_t n;
|
|
if (gcstate->collecting) {
|
|
/* already collecting, don't do anything */
|
|
n = 0;
|
|
}
|
|
else {
|
|
gcstate->collecting = 1;
|
|
n = collect_with_callback(tstate, generation);
|
|
gcstate->collecting = 0;
|
|
}
|
|
return n;
|
|
}
|
|
|
|
/*[clinic input]
|
|
gc.set_debug
|
|
|
|
flags: int
|
|
An integer that can have the following bits turned on:
|
|
DEBUG_STATS - Print statistics during collection.
|
|
DEBUG_COLLECTABLE - Print collectable objects found.
|
|
DEBUG_UNCOLLECTABLE - Print unreachable but uncollectable objects
|
|
found.
|
|
DEBUG_SAVEALL - Save objects to gc.garbage rather than freeing them.
|
|
DEBUG_LEAK - Debug leaking programs (everything but STATS).
|
|
/
|
|
|
|
Set the garbage collection debugging flags.
|
|
|
|
Debugging information is written to sys.stderr.
|
|
[clinic start generated code]*/
|
|
|
|
static PyObject *
|
|
gc_set_debug_impl(PyObject *module, int flags)
|
|
/*[clinic end generated code: output=7c8366575486b228 input=5e5ce15e84fbed15]*/
|
|
{
|
|
PyThreadState *tstate = _PyThreadState_GET();
|
|
GCState *gcstate = &tstate->interp->gc;
|
|
gcstate->debug = flags;
|
|
Py_RETURN_NONE;
|
|
}
|
|
|
|
/*[clinic input]
|
|
gc.get_debug -> int
|
|
|
|
Get the garbage collection debugging flags.
|
|
[clinic start generated code]*/
|
|
|
|
static int
|
|
gc_get_debug_impl(PyObject *module)
|
|
/*[clinic end generated code: output=91242f3506cd1e50 input=91a101e1c3b98366]*/
|
|
{
|
|
PyThreadState *tstate = _PyThreadState_GET();
|
|
GCState *gcstate = &tstate->interp->gc;
|
|
return gcstate->debug;
|
|
}
|
|
|
|
PyDoc_STRVAR(gc_set_thresh__doc__,
|
|
"set_threshold(threshold0, [threshold1, threshold2]) -> None\n"
|
|
"\n"
|
|
"Sets the collection thresholds. Setting threshold0 to zero disables\n"
|
|
"collection.\n");
|
|
|
|
static PyObject *
|
|
gc_set_threshold(PyObject *self, PyObject *args)
|
|
{
|
|
PyThreadState *tstate = _PyThreadState_GET();
|
|
GCState *gcstate = &tstate->interp->gc;
|
|
if (!PyArg_ParseTuple(args, "i|ii:set_threshold",
|
|
&gcstate->generations[0].threshold,
|
|
&gcstate->generations[1].threshold,
|
|
&gcstate->generations[2].threshold))
|
|
return NULL;
|
|
for (int i = 3; i < NUM_GENERATIONS; i++) {
|
|
/* generations higher than 2 get the same threshold */
|
|
gcstate->generations[i].threshold = gcstate->generations[2].threshold;
|
|
}
|
|
Py_RETURN_NONE;
|
|
}
|
|
|
|
/*[clinic input]
|
|
gc.get_threshold
|
|
|
|
Return the current collection thresholds.
|
|
[clinic start generated code]*/
|
|
|
|
static PyObject *
|
|
gc_get_threshold_impl(PyObject *module)
|
|
/*[clinic end generated code: output=7902bc9f41ecbbd8 input=286d79918034d6e6]*/
|
|
{
|
|
PyThreadState *tstate = _PyThreadState_GET();
|
|
GCState *gcstate = &tstate->interp->gc;
|
|
return Py_BuildValue("(iii)",
|
|
gcstate->generations[0].threshold,
|
|
gcstate->generations[1].threshold,
|
|
gcstate->generations[2].threshold);
|
|
}
|
|
|
|
/*[clinic input]
|
|
gc.get_count
|
|
|
|
Return a three-tuple of the current collection counts.
|
|
[clinic start generated code]*/
|
|
|
|
static PyObject *
|
|
gc_get_count_impl(PyObject *module)
|
|
/*[clinic end generated code: output=354012e67b16398f input=a392794a08251751]*/
|
|
{
|
|
PyThreadState *tstate = _PyThreadState_GET();
|
|
GCState *gcstate = &tstate->interp->gc;
|
|
return Py_BuildValue("(iii)",
|
|
gcstate->generations[0].count,
|
|
gcstate->generations[1].count,
|
|
gcstate->generations[2].count);
|
|
}
|
|
|
|
static int
|
|
referrersvisit(PyObject* obj, PyObject *objs)
|
|
{
|
|
Py_ssize_t i;
|
|
for (i = 0; i < PyTuple_GET_SIZE(objs); i++)
|
|
if (PyTuple_GET_ITEM(objs, i) == obj)
|
|
return 1;
|
|
return 0;
|
|
}
|
|
|
|
static int
|
|
gc_referrers_for(PyObject *objs, PyGC_Head *list, PyObject *resultlist)
|
|
{
|
|
PyGC_Head *gc;
|
|
PyObject *obj;
|
|
traverseproc traverse;
|
|
for (gc = GC_NEXT(list); gc != list; gc = GC_NEXT(gc)) {
|
|
obj = FROM_GC(gc);
|
|
traverse = Py_TYPE(obj)->tp_traverse;
|
|
if (obj == objs || obj == resultlist)
|
|
continue;
|
|
if (traverse(obj, (visitproc)referrersvisit, objs)) {
|
|
if (PyList_Append(resultlist, obj) < 0)
|
|
return 0; /* error */
|
|
}
|
|
}
|
|
return 1; /* no error */
|
|
}
|
|
|
|
PyDoc_STRVAR(gc_get_referrers__doc__,
|
|
"get_referrers(*objs) -> list\n\
|
|
Return the list of objects that directly refer to any of objs.");
|
|
|
|
static PyObject *
|
|
gc_get_referrers(PyObject *self, PyObject *args)
|
|
{
|
|
PyThreadState *tstate = _PyThreadState_GET();
|
|
int i;
|
|
PyObject *result = PyList_New(0);
|
|
if (!result) {
|
|
return NULL;
|
|
}
|
|
|
|
GCState *gcstate = &tstate->interp->gc;
|
|
for (i = 0; i < NUM_GENERATIONS; i++) {
|
|
if (!(gc_referrers_for(args, GEN_HEAD(gcstate, i), result))) {
|
|
Py_DECREF(result);
|
|
return NULL;
|
|
}
|
|
}
|
|
return result;
|
|
}
|
|
|
|
/* Append obj to list; return true if error (out of memory), false if OK. */
|
|
static int
|
|
referentsvisit(PyObject *obj, PyObject *list)
|
|
{
|
|
return PyList_Append(list, obj) < 0;
|
|
}
|
|
|
|
PyDoc_STRVAR(gc_get_referents__doc__,
|
|
"get_referents(*objs) -> list\n\
|
|
Return the list of objects that are directly referred to by objs.");
|
|
|
|
static PyObject *
|
|
gc_get_referents(PyObject *self, PyObject *args)
|
|
{
|
|
Py_ssize_t i;
|
|
PyObject *result = PyList_New(0);
|
|
|
|
if (result == NULL)
|
|
return NULL;
|
|
|
|
for (i = 0; i < PyTuple_GET_SIZE(args); i++) {
|
|
traverseproc traverse;
|
|
PyObject *obj = PyTuple_GET_ITEM(args, i);
|
|
|
|
if (! PyObject_IS_GC(obj))
|
|
continue;
|
|
traverse = Py_TYPE(obj)->tp_traverse;
|
|
if (! traverse)
|
|
continue;
|
|
if (traverse(obj, (visitproc)referentsvisit, result)) {
|
|
Py_DECREF(result);
|
|
return NULL;
|
|
}
|
|
}
|
|
return result;
|
|
}
|
|
|
|
/*[clinic input]
|
|
gc.get_objects
|
|
generation: Py_ssize_t(accept={int, NoneType}, c_default="-1") = None
|
|
Generation to extract the objects from.
|
|
|
|
Return a list of objects tracked by the collector (excluding the list returned).
|
|
|
|
If generation is not None, return only the objects tracked by the collector
|
|
that are in that generation.
|
|
[clinic start generated code]*/
|
|
|
|
static PyObject *
|
|
gc_get_objects_impl(PyObject *module, Py_ssize_t generation)
|
|
/*[clinic end generated code: output=48b35fea4ba6cb0e input=ef7da9df9806754c]*/
|
|
{
|
|
PyThreadState *tstate = _PyThreadState_GET();
|
|
int i;
|
|
PyObject* result;
|
|
GCState *gcstate = &tstate->interp->gc;
|
|
|
|
result = PyList_New(0);
|
|
if (result == NULL) {
|
|
return NULL;
|
|
}
|
|
|
|
/* If generation is passed, we extract only that generation */
|
|
if (generation != -1) {
|
|
if (generation >= NUM_GENERATIONS) {
|
|
_PyErr_Format(tstate, PyExc_ValueError,
|
|
"generation parameter must be less than the number of "
|
|
"available generations (%i)",
|
|
NUM_GENERATIONS);
|
|
goto error;
|
|
}
|
|
|
|
if (generation < 0) {
|
|
_PyErr_SetString(tstate, PyExc_ValueError,
|
|
"generation parameter cannot be negative");
|
|
goto error;
|
|
}
|
|
|
|
if (append_objects(result, GEN_HEAD(gcstate, generation))) {
|
|
goto error;
|
|
}
|
|
|
|
return result;
|
|
}
|
|
|
|
/* If generation is not passed or None, get all objects from all generations */
|
|
for (i = 0; i < NUM_GENERATIONS; i++) {
|
|
if (append_objects(result, GEN_HEAD(gcstate, i))) {
|
|
goto error;
|
|
}
|
|
}
|
|
return result;
|
|
|
|
error:
|
|
Py_DECREF(result);
|
|
return NULL;
|
|
}
|
|
|
|
/*[clinic input]
|
|
gc.get_stats
|
|
|
|
Return a list of dictionaries containing per-generation statistics.
|
|
[clinic start generated code]*/
|
|
|
|
static PyObject *
|
|
gc_get_stats_impl(PyObject *module)
|
|
/*[clinic end generated code: output=a8ab1d8a5d26f3ab input=1ef4ed9d17b1a470]*/
|
|
{
|
|
int i;
|
|
struct gc_generation_stats stats[NUM_GENERATIONS], *st;
|
|
PyThreadState *tstate = _PyThreadState_GET();
|
|
|
|
/* To get consistent values despite allocations while constructing
|
|
the result list, we use a snapshot of the running stats. */
|
|
GCState *gcstate = &tstate->interp->gc;
|
|
for (i = 0; i < NUM_GENERATIONS; i++) {
|
|
stats[i] = gcstate->generation_stats[i];
|
|
}
|
|
|
|
PyObject *result = PyList_New(0);
|
|
if (result == NULL)
|
|
return NULL;
|
|
|
|
for (i = 0; i < NUM_GENERATIONS; i++) {
|
|
PyObject *dict;
|
|
st = &stats[i];
|
|
dict = Py_BuildValue("{snsnsn}",
|
|
"collections", st->collections,
|
|
"collected", st->collected,
|
|
"uncollectable", st->uncollectable
|
|
);
|
|
if (dict == NULL)
|
|
goto error;
|
|
if (PyList_Append(result, dict)) {
|
|
Py_DECREF(dict);
|
|
goto error;
|
|
}
|
|
Py_DECREF(dict);
|
|
}
|
|
return result;
|
|
|
|
error:
|
|
Py_XDECREF(result);
|
|
return NULL;
|
|
}
|
|
|
|
|
|
/*[clinic input]
|
|
gc.is_tracked
|
|
|
|
obj: object
|
|
/
|
|
|
|
Returns true if the object is tracked by the garbage collector.
|
|
|
|
Simple atomic objects will return false.
|
|
[clinic start generated code]*/
|
|
|
|
static PyObject *
|
|
gc_is_tracked(PyObject *module, PyObject *obj)
|
|
/*[clinic end generated code: output=14f0103423b28e31 input=d83057f170ea2723]*/
|
|
{
|
|
PyObject *result;
|
|
|
|
if (PyObject_IS_GC(obj) && _PyObject_GC_IS_TRACKED(obj))
|
|
result = Py_True;
|
|
else
|
|
result = Py_False;
|
|
Py_INCREF(result);
|
|
return result;
|
|
}
|
|
|
|
/*[clinic input]
|
|
gc.freeze
|
|
|
|
Freeze all current tracked objects and ignore them for future collections.
|
|
|
|
This can be used before a POSIX fork() call to make the gc copy-on-write friendly.
|
|
Note: collection before a POSIX fork() call may free pages for future allocation
|
|
which can cause copy-on-write.
|
|
[clinic start generated code]*/
|
|
|
|
static PyObject *
|
|
gc_freeze_impl(PyObject *module)
|
|
/*[clinic end generated code: output=502159d9cdc4c139 input=b602b16ac5febbe5]*/
|
|
{
|
|
PyThreadState *tstate = _PyThreadState_GET();
|
|
GCState *gcstate = &tstate->interp->gc;
|
|
for (int i = 0; i < NUM_GENERATIONS; ++i) {
|
|
gc_list_merge(GEN_HEAD(gcstate, i), &gcstate->permanent_generation.head);
|
|
gcstate->generations[i].count = 0;
|
|
}
|
|
Py_RETURN_NONE;
|
|
}
|
|
|
|
/*[clinic input]
|
|
gc.unfreeze
|
|
|
|
Unfreeze all objects in the permanent generation.
|
|
|
|
Put all objects in the permanent generation back into oldest generation.
|
|
[clinic start generated code]*/
|
|
|
|
static PyObject *
|
|
gc_unfreeze_impl(PyObject *module)
|
|
/*[clinic end generated code: output=1c15f2043b25e169 input=2dd52b170f4cef6c]*/
|
|
{
|
|
PyThreadState *tstate = _PyThreadState_GET();
|
|
GCState *gcstate = &tstate->interp->gc;
|
|
gc_list_merge(&gcstate->permanent_generation.head,
|
|
GEN_HEAD(gcstate, NUM_GENERATIONS-1));
|
|
Py_RETURN_NONE;
|
|
}
|
|
|
|
/*[clinic input]
|
|
gc.get_freeze_count -> Py_ssize_t
|
|
|
|
Return the number of objects in the permanent generation.
|
|
[clinic start generated code]*/
|
|
|
|
static Py_ssize_t
|
|
gc_get_freeze_count_impl(PyObject *module)
|
|
/*[clinic end generated code: output=61cbd9f43aa032e1 input=45ffbc65cfe2a6ed]*/
|
|
{
|
|
PyThreadState *tstate = _PyThreadState_GET();
|
|
GCState *gcstate = &tstate->interp->gc;
|
|
return gc_list_size(&gcstate->permanent_generation.head);
|
|
}
|
|
|
|
|
|
PyDoc_STRVAR(gc__doc__,
|
|
"This module provides access to the garbage collector for reference cycles.\n"
|
|
"\n"
|
|
"enable() -- Enable automatic garbage collection.\n"
|
|
"disable() -- Disable automatic garbage collection.\n"
|
|
"isenabled() -- Returns true if automatic collection is enabled.\n"
|
|
"collect() -- Do a full collection right now.\n"
|
|
"get_count() -- Return the current collection counts.\n"
|
|
"get_stats() -- Return list of dictionaries containing per-generation stats.\n"
|
|
"set_debug() -- Set debugging flags.\n"
|
|
"get_debug() -- Get debugging flags.\n"
|
|
"set_threshold() -- Set the collection thresholds.\n"
|
|
"get_threshold() -- Return the current the collection thresholds.\n"
|
|
"get_objects() -- Return a list of all objects tracked by the collector.\n"
|
|
"is_tracked() -- Returns true if a given object is tracked.\n"
|
|
"get_referrers() -- Return the list of objects that refer to an object.\n"
|
|
"get_referents() -- Return the list of objects that an object refers to.\n"
|
|
"freeze() -- Freeze all tracked objects and ignore them for future collections.\n"
|
|
"unfreeze() -- Unfreeze all objects in the permanent generation.\n"
|
|
"get_freeze_count() -- Return the number of objects in the permanent generation.\n");
|
|
|
|
static PyMethodDef GcMethods[] = {
|
|
GC_ENABLE_METHODDEF
|
|
GC_DISABLE_METHODDEF
|
|
GC_ISENABLED_METHODDEF
|
|
GC_SET_DEBUG_METHODDEF
|
|
GC_GET_DEBUG_METHODDEF
|
|
GC_GET_COUNT_METHODDEF
|
|
{"set_threshold", gc_set_threshold, METH_VARARGS, gc_set_thresh__doc__},
|
|
GC_GET_THRESHOLD_METHODDEF
|
|
GC_COLLECT_METHODDEF
|
|
GC_GET_OBJECTS_METHODDEF
|
|
GC_GET_STATS_METHODDEF
|
|
GC_IS_TRACKED_METHODDEF
|
|
{"get_referrers", gc_get_referrers, METH_VARARGS,
|
|
gc_get_referrers__doc__},
|
|
{"get_referents", gc_get_referents, METH_VARARGS,
|
|
gc_get_referents__doc__},
|
|
GC_FREEZE_METHODDEF
|
|
GC_UNFREEZE_METHODDEF
|
|
GC_GET_FREEZE_COUNT_METHODDEF
|
|
{NULL, NULL} /* Sentinel */
|
|
};
|
|
|
|
static struct PyModuleDef gcmodule = {
|
|
PyModuleDef_HEAD_INIT,
|
|
"gc", /* m_name */
|
|
gc__doc__, /* m_doc */
|
|
-1, /* m_size */
|
|
GcMethods, /* m_methods */
|
|
NULL, /* m_reload */
|
|
NULL, /* m_traverse */
|
|
NULL, /* m_clear */
|
|
NULL /* m_free */
|
|
};
|
|
|
|
PyMODINIT_FUNC
|
|
PyInit_gc(void)
|
|
{
|
|
PyThreadState *tstate = _PyThreadState_GET();
|
|
GCState *gcstate = &tstate->interp->gc;
|
|
|
|
PyObject *m = PyModule_Create(&gcmodule);
|
|
|
|
if (m == NULL) {
|
|
return NULL;
|
|
}
|
|
|
|
if (gcstate->garbage == NULL) {
|
|
gcstate->garbage = PyList_New(0);
|
|
if (gcstate->garbage == NULL) {
|
|
return NULL;
|
|
}
|
|
}
|
|
Py_INCREF(gcstate->garbage);
|
|
if (PyModule_AddObject(m, "garbage", gcstate->garbage) < 0) {
|
|
return NULL;
|
|
}
|
|
|
|
if (gcstate->callbacks == NULL) {
|
|
gcstate->callbacks = PyList_New(0);
|
|
if (gcstate->callbacks == NULL) {
|
|
return NULL;
|
|
}
|
|
}
|
|
Py_INCREF(gcstate->callbacks);
|
|
if (PyModule_AddObject(m, "callbacks", gcstate->callbacks) < 0) {
|
|
return NULL;
|
|
}
|
|
|
|
#define ADD_INT(NAME) if (PyModule_AddIntConstant(m, #NAME, NAME) < 0) { return NULL; }
|
|
ADD_INT(DEBUG_STATS);
|
|
ADD_INT(DEBUG_COLLECTABLE);
|
|
ADD_INT(DEBUG_UNCOLLECTABLE);
|
|
ADD_INT(DEBUG_SAVEALL);
|
|
ADD_INT(DEBUG_LEAK);
|
|
#undef ADD_INT
|
|
return m;
|
|
}
|
|
|
|
/* API to invoke gc.collect() from C */
|
|
Py_ssize_t
|
|
PyGC_Collect(void)
|
|
{
|
|
PyThreadState *tstate = _PyThreadState_GET();
|
|
GCState *gcstate = &tstate->interp->gc;
|
|
|
|
if (!gcstate->enabled) {
|
|
return 0;
|
|
}
|
|
|
|
Py_ssize_t n;
|
|
if (gcstate->collecting) {
|
|
/* already collecting, don't do anything */
|
|
n = 0;
|
|
}
|
|
else {
|
|
PyObject *exc, *value, *tb;
|
|
gcstate->collecting = 1;
|
|
_PyErr_Fetch(tstate, &exc, &value, &tb);
|
|
n = collect_with_callback(tstate, NUM_GENERATIONS - 1);
|
|
_PyErr_Restore(tstate, exc, value, tb);
|
|
gcstate->collecting = 0;
|
|
}
|
|
|
|
return n;
|
|
}
|
|
|
|
Py_ssize_t
|
|
_PyGC_CollectIfEnabled(void)
|
|
{
|
|
return PyGC_Collect();
|
|
}
|
|
|
|
Py_ssize_t
|
|
_PyGC_CollectNoFail(void)
|
|
{
|
|
PyThreadState *tstate = _PyThreadState_GET();
|
|
assert(!_PyErr_Occurred(tstate));
|
|
|
|
GCState *gcstate = &tstate->interp->gc;
|
|
Py_ssize_t n;
|
|
|
|
/* Ideally, this function is only called on interpreter shutdown,
|
|
and therefore not recursively. Unfortunately, when there are daemon
|
|
threads, a daemon thread can start a cyclic garbage collection
|
|
during interpreter shutdown (and then never finish it).
|
|
See http://bugs.python.org/issue8713#msg195178 for an example.
|
|
*/
|
|
if (gcstate->collecting) {
|
|
n = 0;
|
|
}
|
|
else {
|
|
gcstate->collecting = 1;
|
|
n = collect(tstate, NUM_GENERATIONS - 1, NULL, NULL, 1);
|
|
gcstate->collecting = 0;
|
|
}
|
|
return n;
|
|
}
|
|
|
|
void
|
|
_PyGC_DumpShutdownStats(PyThreadState *tstate)
|
|
{
|
|
GCState *gcstate = &tstate->interp->gc;
|
|
if (!(gcstate->debug & DEBUG_SAVEALL)
|
|
&& gcstate->garbage != NULL && PyList_GET_SIZE(gcstate->garbage) > 0) {
|
|
const char *message;
|
|
if (gcstate->debug & DEBUG_UNCOLLECTABLE)
|
|
message = "gc: %zd uncollectable objects at " \
|
|
"shutdown";
|
|
else
|
|
message = "gc: %zd uncollectable objects at " \
|
|
"shutdown; use gc.set_debug(gc.DEBUG_UNCOLLECTABLE) to list them";
|
|
/* PyErr_WarnFormat does too many things and we are at shutdown,
|
|
the warnings module's dependencies (e.g. linecache) may be gone
|
|
already. */
|
|
if (PyErr_WarnExplicitFormat(PyExc_ResourceWarning, "gc", 0,
|
|
"gc", NULL, message,
|
|
PyList_GET_SIZE(gcstate->garbage)))
|
|
PyErr_WriteUnraisable(NULL);
|
|
if (gcstate->debug & DEBUG_UNCOLLECTABLE) {
|
|
PyObject *repr = NULL, *bytes = NULL;
|
|
repr = PyObject_Repr(gcstate->garbage);
|
|
if (!repr || !(bytes = PyUnicode_EncodeFSDefault(repr)))
|
|
PyErr_WriteUnraisable(gcstate->garbage);
|
|
else {
|
|
PySys_WriteStderr(
|
|
" %s\n",
|
|
PyBytes_AS_STRING(bytes)
|
|
);
|
|
}
|
|
Py_XDECREF(repr);
|
|
Py_XDECREF(bytes);
|
|
}
|
|
}
|
|
}
|
|
|
|
void
|
|
_PyGC_Fini(PyThreadState *tstate)
|
|
{
|
|
GCState *gcstate = &tstate->interp->gc;
|
|
Py_CLEAR(gcstate->garbage);
|
|
Py_CLEAR(gcstate->callbacks);
|
|
}
|
|
|
|
/* for debugging */
|
|
void
|
|
_PyGC_Dump(PyGC_Head *g)
|
|
{
|
|
_PyObject_Dump(FROM_GC(g));
|
|
}
|
|
|
|
|
|
#ifdef Py_DEBUG
|
|
static int
|
|
visit_validate(PyObject *op, void *parent_raw)
|
|
{
|
|
PyObject *parent = _PyObject_CAST(parent_raw);
|
|
if (_PyObject_IsFreed(op)) {
|
|
_PyObject_ASSERT_FAILED_MSG(parent,
|
|
"PyObject_GC_Track() object is not valid");
|
|
}
|
|
return 0;
|
|
}
|
|
#endif
|
|
|
|
|
|
/* extension modules might be compiled with GC support so these
|
|
functions must always be available */
|
|
|
|
void
|
|
PyObject_GC_Track(void *op_raw)
|
|
{
|
|
PyObject *op = _PyObject_CAST(op_raw);
|
|
if (_PyObject_GC_IS_TRACKED(op)) {
|
|
_PyObject_ASSERT_FAILED_MSG(op,
|
|
"object already tracked "
|
|
"by the garbage collector");
|
|
}
|
|
_PyObject_GC_TRACK(op);
|
|
|
|
#ifdef Py_DEBUG
|
|
/* Check that the object is valid: validate objects traversed
|
|
by tp_traverse() */
|
|
traverseproc traverse = Py_TYPE(op)->tp_traverse;
|
|
(void)traverse(op, visit_validate, op);
|
|
#endif
|
|
}
|
|
|
|
void
|
|
PyObject_GC_UnTrack(void *op_raw)
|
|
{
|
|
PyObject *op = _PyObject_CAST(op_raw);
|
|
/* Obscure: the Py_TRASHCAN mechanism requires that we be able to
|
|
* call PyObject_GC_UnTrack twice on an object.
|
|
*/
|
|
if (_PyObject_GC_IS_TRACKED(op)) {
|
|
_PyObject_GC_UNTRACK(op);
|
|
}
|
|
}
|
|
|
|
static PyObject *
|
|
_PyObject_GC_Alloc(int use_calloc, size_t basicsize)
|
|
{
|
|
PyThreadState *tstate = _PyThreadState_GET();
|
|
GCState *gcstate = &tstate->interp->gc;
|
|
if (basicsize > PY_SSIZE_T_MAX - sizeof(PyGC_Head)) {
|
|
return _PyErr_NoMemory(tstate);
|
|
}
|
|
size_t size = sizeof(PyGC_Head) + basicsize;
|
|
|
|
PyGC_Head *g;
|
|
if (use_calloc) {
|
|
g = (PyGC_Head *)PyObject_Calloc(1, size);
|
|
}
|
|
else {
|
|
g = (PyGC_Head *)PyObject_Malloc(size);
|
|
}
|
|
if (g == NULL) {
|
|
return _PyErr_NoMemory(tstate);
|
|
}
|
|
assert(((uintptr_t)g & 3) == 0); // g must be aligned 4bytes boundary
|
|
|
|
g->_gc_next = 0;
|
|
g->_gc_prev = 0;
|
|
gcstate->generations[0].count++; /* number of allocated GC objects */
|
|
if (gcstate->generations[0].count > gcstate->generations[0].threshold &&
|
|
gcstate->enabled &&
|
|
gcstate->generations[0].threshold &&
|
|
!gcstate->collecting &&
|
|
!_PyErr_Occurred(tstate))
|
|
{
|
|
gcstate->collecting = 1;
|
|
collect_generations(tstate);
|
|
gcstate->collecting = 0;
|
|
}
|
|
PyObject *op = FROM_GC(g);
|
|
return op;
|
|
}
|
|
|
|
PyObject *
|
|
_PyObject_GC_Malloc(size_t basicsize)
|
|
{
|
|
return _PyObject_GC_Alloc(0, basicsize);
|
|
}
|
|
|
|
PyObject *
|
|
_PyObject_GC_Calloc(size_t basicsize)
|
|
{
|
|
return _PyObject_GC_Alloc(1, basicsize);
|
|
}
|
|
|
|
PyObject *
|
|
_PyObject_GC_New(PyTypeObject *tp)
|
|
{
|
|
PyObject *op = _PyObject_GC_Malloc(_PyObject_SIZE(tp));
|
|
if (op != NULL)
|
|
op = PyObject_INIT(op, tp);
|
|
return op;
|
|
}
|
|
|
|
PyVarObject *
|
|
_PyObject_GC_NewVar(PyTypeObject *tp, Py_ssize_t nitems)
|
|
{
|
|
size_t size;
|
|
PyVarObject *op;
|
|
|
|
if (nitems < 0) {
|
|
PyErr_BadInternalCall();
|
|
return NULL;
|
|
}
|
|
size = _PyObject_VAR_SIZE(tp, nitems);
|
|
op = (PyVarObject *) _PyObject_GC_Malloc(size);
|
|
if (op != NULL)
|
|
op = PyObject_INIT_VAR(op, tp, nitems);
|
|
return op;
|
|
}
|
|
|
|
PyVarObject *
|
|
_PyObject_GC_Resize(PyVarObject *op, Py_ssize_t nitems)
|
|
{
|
|
const size_t basicsize = _PyObject_VAR_SIZE(Py_TYPE(op), nitems);
|
|
_PyObject_ASSERT((PyObject *)op, !_PyObject_GC_IS_TRACKED(op));
|
|
if (basicsize > PY_SSIZE_T_MAX - sizeof(PyGC_Head)) {
|
|
return (PyVarObject *)PyErr_NoMemory();
|
|
}
|
|
|
|
PyGC_Head *g = AS_GC(op);
|
|
g = (PyGC_Head *)PyObject_REALLOC(g, sizeof(PyGC_Head) + basicsize);
|
|
if (g == NULL)
|
|
return (PyVarObject *)PyErr_NoMemory();
|
|
op = (PyVarObject *) FROM_GC(g);
|
|
Py_SIZE(op) = nitems;
|
|
return op;
|
|
}
|
|
|
|
void
|
|
PyObject_GC_Del(void *op)
|
|
{
|
|
PyGC_Head *g = AS_GC(op);
|
|
if (_PyObject_GC_IS_TRACKED(op)) {
|
|
gc_list_remove(g);
|
|
}
|
|
PyThreadState *tstate = _PyThreadState_GET();
|
|
GCState *gcstate = &tstate->interp->gc;
|
|
if (gcstate->generations[0].count > 0) {
|
|
gcstate->generations[0].count--;
|
|
}
|
|
PyObject_FREE(g);
|
|
}
|
|
|
|
/* ------------------------------------------------------------------------
|
|
Notes
|
|
|
|
[REACHABLE OR UNREACHABLE?]
|
|
|
|
It "sounds slick" to move the unreachable objects, until you think about
|
|
it - the reason it pays isn't actually obvious.
|
|
|
|
Suppose we create objects A, B, C in that order. They appear in the young
|
|
generation in the same order. If B points to A, and C to B, and C is
|
|
reachable from outside, then the adjusted refcounts will be 0, 0, and 1
|
|
respectively.
|
|
|
|
When move_unreachable finds A, A is moved to the unreachable list. The
|
|
same for B when it's first encountered. Then C is traversed, B is moved
|
|
_back_ to the reachable list. B is eventually traversed, and then A is
|
|
moved back to the reachable list.
|
|
|
|
So instead of not moving at all, the reachable objects B and A are moved
|
|
twice each. Why is this a win? A straightforward algorithm to move the
|
|
reachable objects instead would move A, B, and C once each.
|
|
|
|
The key is that this dance leaves the objects in order C, B, A - it's
|
|
reversed from the original order. On all _subsequent_ scans, none of
|
|
them will move. Since most objects aren't in cycles, this can save an
|
|
unbounded number of moves across an unbounded number of later collections.
|
|
It can cost more only the first time the chain is scanned.
|
|
|
|
Drawback: move_unreachable is also used to find out what's still trash
|
|
after finalizers may resurrect objects. In _that_ case most unreachable
|
|
objects will remain unreachable, so it would be more efficient to move
|
|
the reachable objects instead. But this is a one-time cost, probably not
|
|
worth complicating the code to speed just a little.
|
|
------------------------------------------------------------------------ */
|
|
|