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gh-110481: Implement inter-thread queue for biased reference counting (#114824)

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Biased reference counting maintains two refcount fields in each object:
`ob_ref_local` and `ob_ref_shared`. The true refcount is the sum of these two
fields. In some cases, when refcounting operations are split across threads,
the ob_ref_shared field can be negative (although the total refcount must be
at least zero). In this case, the thread that decremented the refcount
requests that the owning thread give up ownership and merge the refcount
fields.
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Sam Gross 2024-02-09 17:08:32 -05:00 • committed by GitHub
parent a225520af9
commit a3af3cb4f4
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21 changed files with 418 additions and 11 deletions
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Python/pystate.c
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@ -611,6 +611,9 @@ init_interpreter(PyInterpreterState *interp,
_PyGC_InitState(&interp->gc);
PyConfig_InitPythonConfig(&interp->config);
_PyType_InitCache(interp);
#ifdef Py_GIL_DISABLED
_Py_brc_init_state(interp);
#endif
for (int i = 0; i < _PY_MONITORING_UNGROUPED_EVENTS; i++) {
interp->monitors.tools[i] = 0;
}
@ -1336,6 +1339,11 @@ init_threadstate(_PyThreadStateImpl *_tstate,
tstate->datastack_limit = NULL;
tstate->what_event = -1;
#ifdef Py_GIL_DISABLED
// Initialize biased reference counting inter-thread queue
_Py_brc_init_thread(tstate);
#endif
if (interp->stoptheworld.requested || _PyRuntime.stoptheworld.requested) {
// Start in the suspended state if there is an ongoing stop-the-world.
tstate->state = _Py_THREAD_SUSPENDED;
@ -1561,6 +1569,9 @@ PyThreadState_Clear(PyThreadState *tstate)
_PyFreeListState *freelist_state = &((_PyThreadStateImpl*)tstate)->freelist_state;
_Py_ClearFreeLists(freelist_state, 1);
_PySlice_ClearCache(freelist_state);
// Remove ourself from the biased reference counting table of threads.
_Py_brc_remove_thread(tstate);
#endif
_PyThreadState_ClearMimallocHeaps(tstate);