cpython/Modules/_threadmodule.c

/* Thread module */
/* Interface to Sjoerd's portable C thread library */

#include "Python.h"

#ifndef WITH_THREAD
#error "Error!  The rest of Python is not compiled with thread support."
#error "Rerun configure, adding a --with-threads option."
#error "Then run `make clean' followed by `make'."
#endif

#include "pythread.h"

static PyObject *ThreadError;


/* Lock objects */

typedef struct {
    PyObject_HEAD
    PyThread_type_lock lock_lock;
} lockobject;

static void
lock_dealloc(lockobject *self)
{
    if (self->lock_lock != NULL) {
        /* Unlock the lock so it's safe to free it */
        PyThread_acquire_lock(self->lock_lock, 0);
        PyThread_release_lock(self->lock_lock);

        PyThread_free_lock(self->lock_lock);
    }
    PyObject_Del(self);
}

static PyObject *
lock_PyThread_acquire_lock(lockobject *self, PyObject *args)
{
    int i = 1;

    if (!PyArg_ParseTuple(args, "|i:acquire", &i))
        return NULL;

    Py_BEGIN_ALLOW_THREADS
    i = PyThread_acquire_lock(self->lock_lock, i);
    Py_END_ALLOW_THREADS

    return PyBool_FromLong((long)i);
}

PyDoc_STRVAR(acquire_doc,
"acquire([wait]) -> None or bool\n\
(acquire_lock() is an obsolete synonym)\n\
\n\
Lock the lock.  Without argument, this blocks if the lock is already\n\
locked (even by the same thread), waiting for another thread to release\n\
the lock, and return None once the lock is acquired.\n\
With an argument, this will only block if the argument is true,\n\
and the return value reflects whether the lock is acquired.\n\
The blocking operation is not interruptible.");

static PyObject *
lock_PyThread_release_lock(lockobject *self)
{
    /* Sanity check: the lock must be locked */
    if (PyThread_acquire_lock(self->lock_lock, 0)) {
        PyThread_release_lock(self->lock_lock);
        PyErr_SetString(ThreadError, "release unlocked lock");
        return NULL;
    }

    PyThread_release_lock(self->lock_lock);
    Py_INCREF(Py_None);
    return Py_None;
}

PyDoc_STRVAR(release_doc,
"release()\n\
(release_lock() is an obsolete synonym)\n\
\n\
Release the lock, allowing another thread that is blocked waiting for\n\
the lock to acquire the lock.  The lock must be in the locked state,\n\
but it needn't be locked by the same thread that unlocks it.");

static PyObject *
lock_locked_lock(lockobject *self)
{
    if (PyThread_acquire_lock(self->lock_lock, 0)) {
        PyThread_release_lock(self->lock_lock);
        return PyBool_FromLong(0L);
    }
    return PyBool_FromLong(1L);
}

PyDoc_STRVAR(locked_doc,
"locked() -> bool\n\
(locked_lock() is an obsolete synonym)\n\
\n\
Return whether the lock is in the locked state.");

static PyMethodDef lock_methods[] = {
    {"acquire_lock", (PyCFunction)lock_PyThread_acquire_lock,
     METH_VARARGS, acquire_doc},
    {"acquire",      (PyCFunction)lock_PyThread_acquire_lock,
     METH_VARARGS, acquire_doc},
    {"release_lock", (PyCFunction)lock_PyThread_release_lock,
     METH_NOARGS, release_doc},
    {"release",      (PyCFunction)lock_PyThread_release_lock,
     METH_NOARGS, release_doc},
    {"locked_lock",  (PyCFunction)lock_locked_lock,
     METH_NOARGS, locked_doc},
    {"locked",       (PyCFunction)lock_locked_lock,
     METH_NOARGS, locked_doc},
    {"__enter__",    (PyCFunction)lock_PyThread_acquire_lock,
     METH_VARARGS, acquire_doc},
    {"__exit__",    (PyCFunction)lock_PyThread_release_lock,
     METH_VARARGS, release_doc},
    {NULL,           NULL}              /* sentinel */
};

static PyTypeObject Locktype = {
    PyVarObject_HEAD_INIT(&PyType_Type, 0)
    "_thread.lock",                     /*tp_name*/
    sizeof(lockobject),                 /*tp_size*/
    0,                                  /*tp_itemsize*/
    /* methods */
    (destructor)lock_dealloc,           /*tp_dealloc*/
    0,                                  /*tp_print*/
    0,                                  /*tp_getattr*/
    0,                                  /*tp_setattr*/
    0,                                  /*tp_reserved*/
    0,                                  /*tp_repr*/
    0,                                  /*tp_as_number*/
    0,                                  /*tp_as_sequence*/
    0,                                  /*tp_as_mapping*/
    0,                                  /*tp_hash*/
    0,                                  /*tp_call*/
    0,                                  /*tp_str*/
    0,                                  /*tp_getattro*/
    0,                                  /*tp_setattro*/
    0,                                  /*tp_as_buffer*/
    Py_TPFLAGS_DEFAULT,                 /*tp_flags*/
    0,                                  /*tp_doc*/
    0,                                  /*tp_traverse*/
    0,                                  /*tp_clear*/
    0,                                  /*tp_richcompare*/
    0,                                  /*tp_weaklistoffset*/
    0,                                  /*tp_iter*/
    0,                                  /*tp_iternext*/
    lock_methods,                       /*tp_methods*/
};

static lockobject *
newlockobject(void)
{
    lockobject *self;
    self = PyObject_New(lockobject, &Locktype);
    if (self == NULL)
        return NULL;
    self->lock_lock = PyThread_allocate_lock();
    if (self->lock_lock == NULL) {
        Py_DECREF(self);
        PyErr_SetString(ThreadError, "can't allocate lock");
        return NULL;
    }
    return self;
}

/* Thread-local objects */

#include "structmember.h"

/* Quick overview:

   We need to be able to reclaim reference cycles as soon as possible
   (both when a thread is being terminated, or a thread-local object
    becomes unreachable from user data).  Constraints:
   - it must not be possible for thread-state dicts to be involved in
     reference cycles (otherwise the cyclic GC will refuse to consider
     objects referenced from a reachable thread-state dict, even though
     local_dealloc would clear them)
   - the death of a thread-state dict must still imply destruction of the
     corresponding local dicts in all thread-local objects.

   Our implementation uses small "localdummy" objects in order to break
   the reference chain. These trivial objects are hashable (using the
   default scheme of identity hashing) and weakrefable.
   Each thread-state holds a separate localdummy for each local object
   (as a /strong reference/),
   and each thread-local object holds a dict mapping /weak references/
   of localdummies to local dicts.

   Therefore:
   - only the thread-state dict holds a strong reference to the dummies
   - only the thread-local object holds a strong reference to the local dicts
   - only outside objects (application- or library-level) hold strong
     references to the thread-local objects
   - as soon as a thread-state dict is destroyed, the weakref callbacks of all
     dummies attached to that thread are called, and destroy the corresponding
     local dicts from thread-local objects
   - as soon as a thread-local object is destroyed, its local dicts are
     destroyed and its dummies are manually removed from all thread states
   - the GC can do its work correctly when a thread-local object is dangling,
     without any interference from the thread-state dicts

   As an additional optimization, each localdummy holds a borrowed reference
   to the corresponding localdict.  This borrowed reference is only used
   by the thread-local object which has created the localdummy, which should
   guarantee that the localdict still exists when accessed.
*/

typedef struct {
    PyObject_HEAD
    PyObject *localdict;        /* Borrowed reference! */
    PyObject *weakreflist;      /* List of weak references to self */
} localdummyobject;

static void
localdummy_dealloc(localdummyobject *self)
{
    if (self->weakreflist != NULL)
        PyObject_ClearWeakRefs((PyObject *) self);
    Py_TYPE(self)->tp_free((PyObject*)self);
}

static PyTypeObject localdummytype = {
    PyVarObject_HEAD_INIT(NULL, 0)
    /* tp_name           */ "_thread._localdummy",
    /* tp_basicsize      */ sizeof(localdummyobject),
    /* tp_itemsize       */ 0,
    /* tp_dealloc        */ (destructor)localdummy_dealloc,
    /* tp_print          */ 0,
    /* tp_getattr        */ 0,
    /* tp_setattr        */ 0,
    /* tp_reserved       */ 0,
    /* tp_repr           */ 0,
    /* tp_as_number      */ 0,
    /* tp_as_sequence    */ 0,
    /* tp_as_mapping     */ 0,
    /* tp_hash           */ 0,
    /* tp_call           */ 0,
    /* tp_str            */ 0,
    /* tp_getattro       */ 0,
    /* tp_setattro       */ 0,
    /* tp_as_buffer      */ 0,
    /* tp_flags          */ Py_TPFLAGS_DEFAULT,
    /* tp_doc            */ "Thread-local dummy",
    /* tp_traverse       */ 0,
    /* tp_clear          */ 0,
    /* tp_richcompare    */ 0,
    /* tp_weaklistoffset */ offsetof(localdummyobject, weakreflist)
};


typedef struct {
    PyObject_HEAD
    PyObject *key;
    PyObject *args;
    PyObject *kw;
    /* The current thread's local dict (necessary for tp_dictoffset) */
    PyObject *dict;
    PyObject *weakreflist;      /* List of weak references to self */
    /* A {localdummy weakref -> localdict} dict */
    PyObject *dummies;
    /* The callback for weakrefs to localdummies */
    PyObject *wr_callback;
} localobject;

/* Forward declaration */
static PyObject *_ldict(localobject *self);
static PyObject *_localdummy_destroyed(PyObject *meth_self, PyObject *dummyweakref);

/* Create and register the dummy for the current thread, as well as the
   corresponding local dict */
static int
_local_create_dummy(localobject *self)
{
    PyObject *tdict, *ldict = NULL, *wr = NULL;
    localdummyobject *dummy = NULL;
    int r;

    tdict = PyThreadState_GetDict();
    if (tdict == NULL) {
        PyErr_SetString(PyExc_SystemError,
                        "Couldn't get thread-state dictionary");
        goto err;
    }

    ldict = PyDict_New();
    if (ldict == NULL)
        goto err;
    dummy = (localdummyobject *) localdummytype.tp_alloc(&localdummytype, 0);
    if (dummy == NULL)
        goto err;
    dummy->localdict = ldict;
    wr = PyWeakref_NewRef((PyObject *) dummy, self->wr_callback);
    if (wr == NULL)
        goto err;

    /* As a side-effect, this will cache the weakref's hash before the
       dummy gets deleted */
    r = PyDict_SetItem(self->dummies, wr, ldict);
    if (r < 0)
        goto err;
    Py_CLEAR(wr);
    r = PyDict_SetItem(tdict, self->key, (PyObject *) dummy);
    if (r < 0)
        goto err;
    Py_CLEAR(dummy);

    Py_CLEAR(self->dict);
    self->dict = ldict;
    return 0;

err:
    Py_XDECREF(ldict);
    Py_XDECREF(wr);
    Py_XDECREF(dummy);
    return -1;
}

static PyObject *
local_new(PyTypeObject *type, PyObject *args, PyObject *kw)
{
    localobject *self;
    PyObject *wr;
    static PyMethodDef wr_callback_def = {
        "_localdummy_destroyed", (PyCFunction) _localdummy_destroyed, METH_O
    };

    if (type->tp_init == PyBaseObject_Type.tp_init
        && ((args && PyObject_IsTrue(args))
        || (kw && PyObject_IsTrue(kw)))) {
        PyErr_SetString(PyExc_TypeError,
                  "Initialization arguments are not supported");
        return NULL;
    }

    self = (localobject *)type->tp_alloc(type, 0);
    if (self == NULL)
        return NULL;

    Py_XINCREF(args);
    self->args = args;
    Py_XINCREF(kw);
    self->kw = kw;
    self->key = PyUnicode_FromFormat("thread.local.%p", self);
    if (self->key == NULL)
        goto err;

    self->dummies = PyDict_New();
    if (self->dummies == NULL)
        goto err;

    /* We use a weak reference to self in the callback closure
       in order to avoid spurious reference cycles */
    wr = PyWeakref_NewRef((PyObject *) self, NULL);
    if (wr == NULL)
        goto err;
    self->wr_callback = PyCFunction_New(&wr_callback_def, wr);
    Py_DECREF(wr);
    if (self->wr_callback == NULL)
        goto err;

    if (_local_create_dummy(self) < 0)
        goto err;

    return (PyObject *)self;

  err:
    Py_DECREF(self);
    return NULL;
}

static int
local_traverse(localobject *self, visitproc visit, void *arg)
{
    Py_VISIT(self->args);
    Py_VISIT(self->kw);
    Py_VISIT(self->dummies);
    Py_VISIT(self->dict);
    return 0;
}

static int
local_clear(localobject *self)
{
    PyThreadState *tstate;
    Py_CLEAR(self->args);
    Py_CLEAR(self->kw);
    Py_CLEAR(self->dummies);
    Py_CLEAR(self->dict);
    Py_CLEAR(self->wr_callback);
    /* Remove all strong references to dummies from the thread states */
    if (self->key
        && (tstate = PyThreadState_Get())
        && tstate->interp) {
        for(tstate = PyInterpreterState_ThreadHead(tstate->interp);
            tstate;
            tstate = PyThreadState_Next(tstate))
            if (tstate->dict &&
                PyDict_GetItem(tstate->dict, self->key))
                PyDict_DelItem(tstate->dict, self->key);
    }
    return 0;
}

static void
local_dealloc(localobject *self)
{
    /* Weakrefs must be invalidated right now, otherwise they can be used
       from code called below, which is very dangerous since Py_REFCNT(self) == 0 */
    if (self->weakreflist != NULL)
        PyObject_ClearWeakRefs((PyObject *) self);

    PyObject_GC_UnTrack(self);

    local_clear(self);
    Py_XDECREF(self->key);
    Py_TYPE(self)->tp_free((PyObject*)self);
}

/* Returns a borrowed reference to the local dict, creating it if necessary */
static PyObject *
_ldict(localobject *self)
{
    PyObject *tdict, *ldict, *dummy;

    tdict = PyThreadState_GetDict();
    if (tdict == NULL) {
        PyErr_SetString(PyExc_SystemError,
                        "Couldn't get thread-state dictionary");
        return NULL;
    }

    dummy = PyDict_GetItem(tdict, self->key);
    if (dummy == NULL) {
        if (_local_create_dummy(self) < 0)
            return NULL;
        ldict = self->dict;

        if (Py_TYPE(self)->tp_init != PyBaseObject_Type.tp_init &&
            Py_TYPE(self)->tp_init((PyObject*)self,
                                   self->args, self->kw) < 0) {
            /* we need to get rid of ldict from thread so
               we create a new one the next time we do an attr
               acces */
            PyDict_DelItem(tdict, self->key);
            return NULL;
        }
    }
    else {
        assert(Py_TYPE(dummy) == &localdummytype);
        ldict = ((localdummyobject *) dummy)->localdict;
    }

    /* The call to tp_init above may have caused another thread to run.
       Install our ldict again. */
    if (self->dict != ldict) {
        Py_INCREF(ldict);
        Py_CLEAR(self->dict);
        self->dict = ldict;
    }

    return ldict;
}

static int
local_setattro(localobject *self, PyObject *name, PyObject *v)
{
    PyObject *ldict;

    ldict = _ldict(self);
    if (ldict == NULL)
        return -1;

    return PyObject_GenericSetAttr((PyObject *)self, name, v);
}

static PyObject *
local_getdict(localobject *self, void *closure)
{
    PyObject *ldict;
    ldict = _ldict(self);
    Py_XINCREF(ldict);
    return ldict;
}

static PyGetSetDef local_getset[] = {
    {"__dict__", (getter)local_getdict, (setter)NULL,
     "Local-data dictionary", NULL},
    {NULL}  /* Sentinel */
};

static PyObject *local_getattro(localobject *, PyObject *);

static PyTypeObject localtype = {
    PyVarObject_HEAD_INIT(NULL, 0)
    /* tp_name           */ "_thread._local",
    /* tp_basicsize      */ sizeof(localobject),
    /* tp_itemsize       */ 0,
    /* tp_dealloc        */ (destructor)local_dealloc,
    /* tp_print          */ 0,
    /* tp_getattr        */ 0,
    /* tp_setattr        */ 0,
    /* tp_reserved       */ 0,
    /* tp_repr           */ 0,
    /* tp_as_number      */ 0,
    /* tp_as_sequence    */ 0,
    /* tp_as_mapping     */ 0,
    /* tp_hash           */ 0,
    /* tp_call           */ 0,
    /* tp_str            */ 0,
    /* tp_getattro       */ (getattrofunc)local_getattro,
    /* tp_setattro       */ (setattrofunc)local_setattro,
    /* tp_as_buffer      */ 0,
    /* tp_flags          */ Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
                                               | Py_TPFLAGS_HAVE_GC,
    /* tp_doc            */ "Thread-local data",
    /* tp_traverse       */ (traverseproc)local_traverse,
    /* tp_clear          */ (inquiry)local_clear,
    /* tp_richcompare    */ 0,
    /* tp_weaklistoffset */ offsetof(localobject, weakreflist),
    /* tp_iter           */ 0,
    /* tp_iternext       */ 0,
    /* tp_methods        */ 0,
    /* tp_members        */ 0,
    /* tp_getset         */ local_getset,
    /* tp_base           */ 0,
    /* tp_dict           */ 0, /* internal use */
    /* tp_descr_get      */ 0,
    /* tp_descr_set      */ 0,
    /* tp_dictoffset     */ offsetof(localobject, dict),
    /* tp_init           */ 0,
    /* tp_alloc          */ 0,
    /* tp_new            */ local_new,
    /* tp_free           */ 0, /* Low-level free-mem routine */
    /* tp_is_gc          */ 0, /* For PyObject_IS_GC */
};

static PyObject *
local_getattro(localobject *self, PyObject *name)
{
    PyObject *ldict, *value;

    ldict = _ldict(self);
    if (ldict == NULL)
        return NULL;

    if (Py_TYPE(self) != &localtype)
        /* use generic lookup for subtypes */
        return PyObject_GenericGetAttr((PyObject *)self, name);

    /* Optimization: just look in dict ourselves */
    value = PyDict_GetItem(ldict, name);
    if (value == NULL)
        /* Fall back on generic to get __class__ and __dict__ */
        return PyObject_GenericGetAttr((PyObject *)self, name);

    Py_INCREF(value);
    return value;
}

/* Called when a dummy is destroyed. */
static PyObject *
_localdummy_destroyed(PyObject *localweakref, PyObject *dummyweakref)
{
    PyObject *obj;
    localobject *self;
    assert(PyWeakref_CheckRef(localweakref));
    obj = PyWeakref_GET_OBJECT(localweakref);
    if (obj == Py_None)
        Py_RETURN_NONE;
    Py_INCREF(obj);
    assert(PyObject_TypeCheck(obj, &localtype));
    /* If the thread-local object is still alive and not being cleared,
       remove the corresponding local dict */
    self = (localobject *) obj;
    if (self->dummies != NULL) {
        PyObject *ldict;
        ldict = PyDict_GetItem(self->dummies, dummyweakref);
        if (ldict != NULL) {
            if (ldict == self->dict)
                Py_CLEAR(self->dict);
            PyDict_DelItem(self->dummies, dummyweakref);
        }
        if (PyErr_Occurred())
            PyErr_WriteUnraisable(obj);
    }
    Py_DECREF(obj);
    Py_RETURN_NONE;
}

/* Module functions */

struct bootstate {
    PyInterpreterState *interp;
    PyObject *func;
    PyObject *args;
    PyObject *keyw;
    PyThreadState *tstate;
};

static void
t_bootstrap(void *boot_raw)
{
    struct bootstate *boot = (struct bootstate *) boot_raw;
    PyThreadState *tstate;
    PyObject *res;

    tstate = boot->tstate;
    tstate->thread_id = PyThread_get_thread_ident();
    _PyThreadState_Init(tstate);
    PyEval_AcquireThread(tstate);
    res = PyEval_CallObjectWithKeywords(
        boot->func, boot->args, boot->keyw);
    if (res == NULL) {
        if (PyErr_ExceptionMatches(PyExc_SystemExit))
            PyErr_Clear();
        else {
            PyObject *file;
            PySys_WriteStderr(
                "Unhandled exception in thread started by ");
            file = PySys_GetObject("stderr");
            if (file != NULL && file != Py_None)
                PyFile_WriteObject(boot->func, file, 0);
            else
                PyObject_Print(boot->func, stderr, 0);
            PySys_WriteStderr("\n");
            PyErr_PrintEx(0);
        }
    }
    else
        Py_DECREF(res);
    Py_DECREF(boot->func);
    Py_DECREF(boot->args);
    Py_XDECREF(boot->keyw);
    PyMem_DEL(boot_raw);
    PyThreadState_Clear(tstate);
    PyThreadState_DeleteCurrent();
    PyThread_exit_thread();
}

static PyObject *
thread_PyThread_start_new_thread(PyObject *self, PyObject *fargs)
{
    PyObject *func, *args, *keyw = NULL;
    struct bootstate *boot;
    long ident;

    if (!PyArg_UnpackTuple(fargs, "start_new_thread", 2, 3,
                           &func, &args, &keyw))
        return NULL;
    if (!PyCallable_Check(func)) {
        PyErr_SetString(PyExc_TypeError,
                        "first arg must be callable");
        return NULL;
    }
    if (!PyTuple_Check(args)) {
        PyErr_SetString(PyExc_TypeError,
                        "2nd arg must be a tuple");
        return NULL;
    }
    if (keyw != NULL && !PyDict_Check(keyw)) {
        PyErr_SetString(PyExc_TypeError,
                        "optional 3rd arg must be a dictionary");
        return NULL;
    }
    boot = PyMem_NEW(struct bootstate, 1);
    if (boot == NULL)
        return PyErr_NoMemory();
    boot->interp = PyThreadState_GET()->interp;
    boot->func = func;
    boot->args = args;
    boot->keyw = keyw;
    boot->tstate = _PyThreadState_Prealloc(boot->interp);
    if (boot->tstate == NULL) {
        PyMem_DEL(boot);
        return PyErr_NoMemory();
    }
    Py_INCREF(func);
    Py_INCREF(args);
    Py_XINCREF(keyw);
    PyEval_InitThreads(); /* Start the interpreter's thread-awareness */
    ident = PyThread_start_new_thread(t_bootstrap, (void*) boot);
    if (ident == -1) {
        PyErr_SetString(ThreadError, "can't start new thread");
        Py_DECREF(func);
        Py_DECREF(args);
        Py_XDECREF(keyw);
        PyThreadState_Clear(boot->tstate);
        PyMem_DEL(boot);
        return NULL;
    }
    return PyLong_FromLong(ident);
}

PyDoc_STRVAR(start_new_doc,
"start_new_thread(function, args[, kwargs])\n\
(start_new() is an obsolete synonym)\n\
\n\
Start a new thread and return its identifier.  The thread will call the\n\
function with positional arguments from the tuple args and keyword arguments\n\
taken from the optional dictionary kwargs.  The thread exits when the\n\
function returns; the return value is ignored.  The thread will also exit\n\
when the function raises an unhandled exception; a stack trace will be\n\
printed unless the exception is SystemExit.\n");

static PyObject *
thread_PyThread_exit_thread(PyObject *self)
{
    PyErr_SetNone(PyExc_SystemExit);
    return NULL;
}

PyDoc_STRVAR(exit_doc,
"exit()\n\
(PyThread_exit_thread() is an obsolete synonym)\n\
\n\
This is synonymous to ``raise SystemExit''.  It will cause the current\n\
thread to exit silently unless the exception is caught.");

static PyObject *
thread_PyThread_interrupt_main(PyObject * self)
{
    PyErr_SetInterrupt();
    Py_INCREF(Py_None);
    return Py_None;
}

PyDoc_STRVAR(interrupt_doc,
"interrupt_main()\n\
\n\
Raise a KeyboardInterrupt in the main thread.\n\
A subthread can use this function to interrupt the main thread."
);

#ifndef NO_EXIT_PROG
static PyObject *
thread_PyThread_exit_prog(PyObject *self, PyObject *args)
{
    int sts;
    if (!PyArg_ParseTuple(args, "i:exit_prog", &sts))
        return NULL;
    Py_Exit(sts); /* Calls PyThread_exit_prog(sts) or _PyThread_exit_prog(sts) */
    for (;;) { } /* Should not be reached */
}
#endif

static lockobject *newlockobject(void);

static PyObject *
thread_PyThread_allocate_lock(PyObject *self)
{
    return (PyObject *) newlockobject();
}

PyDoc_STRVAR(allocate_doc,
"allocate_lock() -> lock object\n\
(allocate() is an obsolete synonym)\n\
\n\
Create a new lock object.  See help(LockType) for information about locks.");

static PyObject *
thread_get_ident(PyObject *self)
{
    long ident;
    ident = PyThread_get_thread_ident();
    if (ident == -1) {
        PyErr_SetString(ThreadError, "no current thread ident");
        return NULL;
    }
    return PyLong_FromLong(ident);
}

PyDoc_STRVAR(get_ident_doc,
"get_ident() -> integer\n\
\n\
Return a non-zero integer that uniquely identifies the current thread\n\
amongst other threads that exist simultaneously.\n\
This may be used to identify per-thread resources.\n\
Even though on some platforms threads identities may appear to be\n\
allocated consecutive numbers starting at 1, this behavior should not\n\
be relied upon, and the number should be seen purely as a magic cookie.\n\
A thread's identity may be reused for another thread after it exits.");

static PyObject *
thread_stack_size(PyObject *self, PyObject *args)
{
    size_t old_size;
    Py_ssize_t new_size = 0;
    int rc;

    if (!PyArg_ParseTuple(args, "|n:stack_size", &new_size))
        return NULL;

    if (new_size < 0) {
        PyErr_SetString(PyExc_ValueError,
                        "size must be 0 or a positive value");
        return NULL;
    }

    old_size = PyThread_get_stacksize();

    rc = PyThread_set_stacksize((size_t) new_size);
    if (rc == -1) {
        PyErr_Format(PyExc_ValueError,
                     "size not valid: %zd bytes",
                     new_size);
        return NULL;
    }
    if (rc == -2) {
        PyErr_SetString(ThreadError,
                        "setting stack size not supported");
        return NULL;
    }

    return PyLong_FromSsize_t((Py_ssize_t) old_size);
}

PyDoc_STRVAR(stack_size_doc,
"stack_size([size]) -> size\n\
\n\
Return the thread stack size used when creating new threads.  The\n\
optional size argument specifies the stack size (in bytes) to be used\n\
for subsequently created threads, and must be 0 (use platform or\n\
configured default) or a positive integer value of at least 32,768 (32k).\n\
If changing the thread stack size is unsupported, a ThreadError\n\
exception is raised.  If the specified size is invalid, a ValueError\n\
exception is raised, and the stack size is unmodified.  32k bytes\n\
 currently the minimum supported stack size value to guarantee\n\
sufficient stack space for the interpreter itself.\n\
\n\
Note that some platforms may have particular restrictions on values for\n\
the stack size, such as requiring a minimum stack size larger than 32kB or\n\
requiring allocation in multiples of the system memory page size\n\
- platform documentation should be referred to for more information\n\
(4kB pages are common; using multiples of 4096 for the stack size is\n\
the suggested approach in the absence of more specific information).");

static PyMethodDef thread_methods[] = {
    {"start_new_thread",        (PyCFunction)thread_PyThread_start_new_thread,
                            METH_VARARGS,
                            start_new_doc},
    {"start_new",               (PyCFunction)thread_PyThread_start_new_thread,
                            METH_VARARGS,
                            start_new_doc},
    {"allocate_lock",           (PyCFunction)thread_PyThread_allocate_lock,
     METH_NOARGS, allocate_doc},
    {"allocate",                (PyCFunction)thread_PyThread_allocate_lock,
     METH_NOARGS, allocate_doc},
    {"exit_thread",             (PyCFunction)thread_PyThread_exit_thread,
     METH_NOARGS, exit_doc},
    {"exit",                    (PyCFunction)thread_PyThread_exit_thread,
     METH_NOARGS, exit_doc},
    {"interrupt_main",          (PyCFunction)thread_PyThread_interrupt_main,
     METH_NOARGS, interrupt_doc},
    {"get_ident",               (PyCFunction)thread_get_ident,
     METH_NOARGS, get_ident_doc},
    {"stack_size",              (PyCFunction)thread_stack_size,
                            METH_VARARGS,
                            stack_size_doc},
#ifndef NO_EXIT_PROG
    {"exit_prog",               (PyCFunction)thread_PyThread_exit_prog,
     METH_VARARGS},
#endif
    {NULL,                      NULL}           /* sentinel */
};


/* Initialization function */

PyDoc_STRVAR(thread_doc,
"This module provides primitive operations to write multi-threaded programs.\n\
The 'threading' module provides a more convenient interface.");

PyDoc_STRVAR(lock_doc,
"A lock object is a synchronization primitive.  To create a lock,\n\
call the PyThread_allocate_lock() function.  Methods are:\n\
\n\
acquire() -- lock the lock, possibly blocking until it can be obtained\n\
release() -- unlock of the lock\n\
locked() -- test whether the lock is currently locked\n\
\n\
A lock is not owned by the thread that locked it; another thread may\n\
unlock it.  A thread attempting to lock a lock that it has already locked\n\
will block until another thread unlocks it.  Deadlocks may ensue.");

static struct PyModuleDef threadmodule = {
    PyModuleDef_HEAD_INIT,
    "_thread",
    thread_doc,
    -1,
    thread_methods,
    NULL,
    NULL,
    NULL,
    NULL
};


PyMODINIT_FUNC
PyInit__thread(void)
{
    PyObject *m, *d;

    /* Initialize types: */
    if (PyType_Ready(&localdummytype) < 0)
        return NULL;
    if (PyType_Ready(&localtype) < 0)
        return NULL;
    if (PyType_Ready(&Locktype) < 0)
        return NULL;

    /* Create the module and add the functions */
    m = PyModule_Create(&threadmodule);
    if (m == NULL)
        return NULL;

    /* Add a symbolic constant */
    d = PyModule_GetDict(m);
    ThreadError = PyErr_NewException("_thread.error", NULL, NULL);
    PyDict_SetItemString(d, "error", ThreadError);
    Locktype.tp_doc = lock_doc;
    Py_INCREF(&Locktype);
    PyDict_SetItemString(d, "LockType", (PyObject *)&Locktype);

    Py_INCREF(&localtype);
    if (PyModule_AddObject(m, "_local", (PyObject *)&localtype) < 0)
        return NULL;

    /* Initialize the C thread library */
    PyThread_init_thread();
    return m;
}