bpo-14976: Reentrant simple queue (#3346)

Add a queue.SimpleQueue class, an unbounded FIFO queue with a reentrant C implementation of put().

Doc/library/queue.rst

@@ -23,8 +23,14 @@ the first retrieved (operating like a stack).  With a priority queue,
 the entries are kept sorted (using the :mod:`heapq` module) and the
 lowest valued entry is retrieved first.
 
-Internally, the module uses locks to temporarily block competing threads;
+Internally, those three types of queues use locks to temporarily block
-however, it is not designed to handle reentrancy within a thread.
+competing threads; however, they are not designed to handle reentrancy
+within a thread.
+
+In addition, the module implements a "simple"
+:abbr:`FIFO (first-in, first-out)` queue type where
+specific implementations can provide additional guarantees
+in exchange for the smaller functionality.
 
 The :mod:`queue` module defines the following classes and exceptions:
 
@@ -67,6 +73,14 @@ The :mod:`queue` module defines the following classes and exceptions:
             priority: int
             item: Any=field(compare=False)
 
+.. class:: SimpleQueue()
+
+   Constructor for an unbounded :abbr:`FIFO (first-in, first-out)` queue.
+   Simple queues lack advanced functionality such as task tracking.
+
+   .. versionadded:: 3.7
+
+
 .. exception:: Empty
 
    Exception raised when non-blocking :meth:`~Queue.get` (or
@@ -201,6 +215,60 @@ Example of how to wait for enqueued tasks to be completed::
         t.join()
 
 
+SimpleQueue Objects
+-------------------
+
+:class:`SimpleQueue` objects provide the public methods described below.
+
+.. method:: SimpleQueue.qsize()
+
+   Return the approximate size of the queue.  Note, qsize() > 0 doesn't
+   guarantee that a subsequent get() will not block.
+
+
+.. method:: SimpleQueue.empty()
+
+   Return ``True`` if the queue is empty, ``False`` otherwise. If empty()
+   returns ``False`` it doesn't guarantee that a subsequent call to get()
+   will not block.
+
+
+.. method:: SimpleQueue.put(item, block=True, timeout=None)
+
+   Put *item* into the queue.  The method never blocks and always succeeds
+   (except for potential low-level errors such as failure to allocate memory).
+   The optional args *block* and *timeout* are ignored and only provided
+   for compatibility with :meth:`Queue.put`.
+
+   .. impl-detail::
+      This method has a C implementation which is reentrant.  That is, a
+      ``put()`` or ``get()`` call can be interrupted by another ``put()``
+      call in the same thread without deadlocking or corrupting internal
+      state inside the queue.  This makes it appropriate for use in
+      destructors such as ``__del__`` methods or :mod:`weakref` callbacks.
+
+
+.. method:: SimpleQueue.put_nowait(item)
+
+   Equivalent to ``put(item)``, provided for compatibility with
+   :meth:`Queue.put_nowait`.
+
+
+.. method:: SimpleQueue.get(block=True, timeout=None)
+
+   Remove and return an item from the queue.  If optional args *block* is true and
+   *timeout* is ``None`` (the default), block if necessary until an item is available.
+   If *timeout* is a positive number, it blocks at most *timeout* seconds and
+   raises the :exc:`Empty` exception if no item was available within that time.
+   Otherwise (*block* is false), return an item if one is immediately available,
+   else raise the :exc:`Empty` exception (*timeout* is ignored in that case).
+
+
+.. method:: SimpleQueue.get_nowait()
+
+   Equivalent to ``get(False)``.
+
+
 .. seealso::
 
    Class :class:`multiprocessing.Queue`
@@ -210,4 +278,3 @@ Example of how to wait for enqueued tasks to be completed::
    :class:`collections.deque` is an alternative implementation of unbounded
    queues with fast atomic :meth:`~collections.deque.append` and
    :meth:`~collections.deque.popleft` operations that do not require locking.
-

Lib/queue.py

@@ -4,9 +4,17 @@
 from collections import deque
 from heapq import heappush, heappop
 from time import monotonic as time
+try:
+    from _queue import SimpleQueue
+except ImportError:
+    SimpleQueue = None
 
-__all__ = ['Empty', 'Full', 'Queue', 'PriorityQueue', 'LifoQueue']
+__all__ = ['Empty', 'Full', 'Queue', 'PriorityQueue', 'LifoQueue', 'SimpleQueue']
 
+
+try:
+    from _queue import Empty
+except AttributeError:
     class Empty(Exception):
         'Exception raised by Queue.get(block=0)/get_nowait().'
         pass
@@ -15,6 +23,7 @@ class Full(Exception):
     'Exception raised by Queue.put(block=0)/put_nowait().'
     pass
 
+
 class Queue:
     '''Create a queue object with a given maximum size.
 
@@ -241,3 +250,72 @@ def _put(self, item):
 
     def _get(self):
         return self.queue.pop()
+
+
+class _PySimpleQueue:
+    '''Simple, unbounded FIFO queue.
+
+    This pure Python implementation is not reentrant.
+    '''
+    # Note: while this pure Python version provides fairness
+    # (by using a threading.Semaphore which is itself fair, being based
+    #  on threading.Condition), fairness is not part of the API contract.
+    # This allows the C version to use a different implementation.
+
+    def __init__(self):
+        self._queue = deque()
+        self._count = threading.Semaphore(0)
+
+    def put(self, item, block=True, timeout=None):
+        '''Put the item on the queue.
+
+        The optional 'block' and 'timeout' arguments are ignored, as this method
+        never blocks.  They are provided for compatibility with the Queue class.
+        '''
+        self._queue.append(item)
+        self._count.release()
+
+    def get(self, block=True, timeout=None):
+        '''Remove and return an item from the queue.
+
+        If optional args 'block' is true and 'timeout' is None (the default),
+        block if necessary until an item is available. If 'timeout' is
+        a non-negative number, it blocks at most 'timeout' seconds and raises
+        the Empty exception if no item was available within that time.
+        Otherwise ('block' is false), return an item if one is immediately
+        available, else raise the Empty exception ('timeout' is ignored
+        in that case).
+        '''
+        if timeout is not None and timeout < 0:
+            raise ValueError("'timeout' must be a non-negative number")
+        if not self._count.acquire(block, timeout):
+            raise Empty
+        return self._queue.popleft()
+
+    def put_nowait(self, item):
+        '''Put an item into the queue without blocking.
+
+        This is exactly equivalent to `put(item)` and is only provided
+        for compatibility with the Queue class.
+        '''
+        return self.put(item, block=False)
+
+    def get_nowait(self):
+        '''Remove and return an item from the queue without blocking.
+
+        Only get an item if one is immediately available. Otherwise
+        raise the Empty exception.
+        '''
+        return self.get(block=False)
+
+    def empty(self):
+        '''Return True if the queue is empty, False otherwise (not reliable!).'''
+        return len(self._queue) == 0
+
+    def qsize(self):
+        '''Return the approximate size of the queue (not reliable!).'''
+        return len(self._queue)
+
+
+if SimpleQueue is None:
+    SimpleQueue = _PySimpleQueue

Lib/test/test_queue.py

@@ -1,12 +1,22 @@
 # Some simple queue module tests, plus some failure conditions
 # to ensure the Queue locks remain stable.
+import collections
+import itertools
 import queue
+import random
+import sys
 import threading
 import time
 import unittest
+import weakref
 from test import support
 
 
+try:
+    import _queue
+except ImportError:
+    _queue = None
+
 QUEUE_SIZE = 5
 
 def qfull(q):
@@ -84,7 +94,7 @@ def setUp(self):
         self.cum = 0
         self.cumlock = threading.Lock()
 
-    def simple_queue_test(self, q):
+    def basic_queue_test(self, q):
         if q.qsize():
             raise RuntimeError("Call this function with an empty queue")
         self.assertTrue(q.empty())
@@ -192,12 +202,12 @@ def test_queue_join(self):
         else:
             self.fail("Did not detect task count going negative")
 
-    def test_simple_queue(self):
+    def test_basic(self):
         # Do it a couple of times on the same queue.
         # Done twice to make sure works with same instance reused.
         q = self.type2test(QUEUE_SIZE)
-        self.simple_queue_test(q)
+        self.basic_queue_test(q)
-        self.simple_queue_test(q)
+        self.basic_queue_test(q)
 
     def test_negative_timeout_raises_exception(self):
         q = self.type2test(QUEUE_SIZE)
@@ -353,5 +363,227 @@ def test_failing_queue(self):
         self.failing_queue_test(q)
 
 
+class BaseSimpleQueueTest:
+
+    def setUp(self):
+        self.q = self.type2test()
+
+    def feed(self, q, seq, rnd):
+        while True:
+            try:
+                val = seq.pop()
+            except IndexError:
+                return
+            q.put(val)
+            if rnd.random() > 0.5:
+                time.sleep(rnd.random() * 1e-3)
+
+    def consume(self, q, results, sentinel):
+        while True:
+            val = q.get()
+            if val == sentinel:
+                return
+            results.append(val)
+
+    def consume_nonblock(self, q, results, sentinel):
+        while True:
+            while True:
+                try:
+                    val = q.get(block=False)
+                except queue.Empty:
+                    time.sleep(1e-5)
+                else:
+                    break
+            if val == sentinel:
+                return
+            results.append(val)
+
+    def consume_timeout(self, q, results, sentinel):
+        while True:
+            while True:
+                try:
+                    val = q.get(timeout=1e-5)
+                except queue.Empty:
+                    pass
+                else:
+                    break
+            if val == sentinel:
+                return
+            results.append(val)
+
+    def run_threads(self, n_feeders, n_consumers, q, inputs,
+                    feed_func, consume_func):
+        results = []
+        sentinel = None
+        seq = inputs + [sentinel] * n_consumers
+        seq.reverse()
+        rnd = random.Random(42)
+
+        exceptions = []
+        def log_exceptions(f):
+            def wrapper(*args, **kwargs):
+                try:
+                    f(*args, **kwargs)
+                except BaseException as e:
+                    exceptions.append(e)
+            return wrapper
+
+        feeders = [threading.Thread(target=log_exceptions(feed_func),
+                                    args=(q, seq, rnd))
+                   for i in range(n_feeders)]
+        consumers = [threading.Thread(target=log_exceptions(consume_func),
+                                      args=(q, results, sentinel))
+                     for i in range(n_consumers)]
+
+        with support.start_threads(feeders + consumers):
+            pass
+
+        self.assertFalse(exceptions)
+        self.assertTrue(q.empty())
+        self.assertEqual(q.qsize(), 0)
+
+        return results
+
+    def test_basic(self):
+        # Basic tests for get(), put() etc.
+        q = self.q
+        self.assertTrue(q.empty())
+        self.assertEqual(q.qsize(), 0)
+        q.put(1)
+        self.assertFalse(q.empty())
+        self.assertEqual(q.qsize(), 1)
+        q.put(2)
+        q.put_nowait(3)
+        q.put(4)
+        self.assertFalse(q.empty())
+        self.assertEqual(q.qsize(), 4)
+
+        self.assertEqual(q.get(), 1)
+        self.assertEqual(q.qsize(), 3)
+
+        self.assertEqual(q.get_nowait(), 2)
+        self.assertEqual(q.qsize(), 2)
+
+        self.assertEqual(q.get(block=False), 3)
+        self.assertFalse(q.empty())
+        self.assertEqual(q.qsize(), 1)
+
+        self.assertEqual(q.get(timeout=0.1), 4)
+        self.assertTrue(q.empty())
+        self.assertEqual(q.qsize(), 0)
+
+        with self.assertRaises(queue.Empty):
+            q.get(block=False)
+        with self.assertRaises(queue.Empty):
+            q.get(timeout=1e-3)
+        with self.assertRaises(queue.Empty):
+            q.get_nowait()
+        self.assertTrue(q.empty())
+        self.assertEqual(q.qsize(), 0)
+
+    def test_negative_timeout_raises_exception(self):
+        q = self.q
+        q.put(1)
+        with self.assertRaises(ValueError):
+            q.get(timeout=-1)
+
+    def test_order(self):
+        # Test a pair of concurrent put() and get()
+        q = self.q
+        inputs = list(range(100))
+        results = self.run_threads(1, 1, q, inputs, self.feed, self.consume)
+
+        # One producer, one consumer => results appended in well-defined order
+        self.assertEqual(results, inputs)
+
+    def test_many_threads(self):
+        # Test multiple concurrent put() and get()
+        N = 50
+        q = self.q
+        inputs = list(range(10000))
+        results = self.run_threads(N, N, q, inputs, self.feed, self.consume)
+
+        # Multiple consumers without synchronization append the
+        # results in random order
+        self.assertEqual(sorted(results), inputs)
+
+    def test_many_threads_nonblock(self):
+        # Test multiple concurrent put() and get(block=False)
+        N = 50
+        q = self.q
+        inputs = list(range(10000))
+        results = self.run_threads(N, N, q, inputs,
+                                   self.feed, self.consume_nonblock)
+
+        self.assertEqual(sorted(results), inputs)
+
+    def test_many_threads_timeout(self):
+        # Test multiple concurrent put() and get(timeout=...)
+        N = 50
+        q = self.q
+        inputs = list(range(1000))
+        results = self.run_threads(N, N, q, inputs,
+                                   self.feed, self.consume_timeout)
+
+        self.assertEqual(sorted(results), inputs)
+
+    def test_references(self):
+        # The queue should lose references to each item as soon as
+        # it leaves the queue.
+        class C:
+            pass
+
+        N = 20
+        q = self.q
+        for i in range(N):
+            q.put(C())
+        for i in range(N):
+            wr = weakref.ref(q.get())
+            self.assertIsNone(wr())
+
+
+class PySimpleQueueTest(BaseSimpleQueueTest, unittest.TestCase):
+    type2test = queue._PySimpleQueue
+
+
+@unittest.skipIf(_queue is None, "No _queue module found")
+class CSimpleQueueTest(BaseSimpleQueueTest, unittest.TestCase):
+
+    def setUp(self):
+        self.type2test = _queue.SimpleQueue
+        super().setUp()
+
+    def test_is_default(self):
+        self.assertIs(self.type2test, queue.SimpleQueue)
+
+    def test_reentrancy(self):
+        # bpo-14976: put() may be called reentrantly in an asynchronous
+        # callback.
+        q = self.q
+        gen = itertools.count()
+        N = 10000
+        results = []
+
+        # This test exploits the fact that __del__ in a reference cycle
+        # can be called any time the GC may run.
+
+        class Circular(object):
+            def __init__(self):
+                self.circular = self
+
+            def __del__(self):
+                q.put(next(gen))
+
+        while True:
+            o = Circular()
+            q.put(next(gen))
+            del o
+            results.append(q.get())
+            if results[-1] >= N:
+                break
+
+        self.assertEqual(results, list(range(N + 1)))
+
+
 if __name__ == "__main__":
     unittest.main()

Misc/NEWS.d/next/Library/2017-09-07-19-12-47.bpo-14976.dx0Zxb.rst

@@ -0,0 +1,2 @@
+Add a queue.SimpleQueue class, an unbounded FIFO queue with a reentrant C
+implementation of put().

Modules/_queuemodule.c

@@ -0,0 +1,400 @@
+#include "Python.h"
+#include "structmember.h" /* offsetof */
+#include "pythread.h"
+
+/*[clinic input]
+module _queue
+class _queue.SimpleQueue "simplequeueobject *" "&PySimpleQueueType"
+[clinic start generated code]*/
+/*[clinic end generated code: output=da39a3ee5e6b4b0d input=cf49af81bcbbbea6]*/
+
+extern PyTypeObject PySimpleQueueType;  /* forward decl */
+
+static PyObject *EmptyError;
+
+
+typedef struct {
+    PyObject_HEAD
+    PyThread_type_lock lock;
+    int locked;
+    PyObject *lst;
+    Py_ssize_t lst_pos;
+    PyObject *weakreflist;
+} simplequeueobject;
+
+
+static void
+simplequeue_dealloc(simplequeueobject *self)
+{
+    _PyObject_GC_UNTRACK(self);
+    if (self->lock != NULL) {
+        /* Unlock the lock so it's safe to free it */
+        if (self->locked > 0)
+            PyThread_release_lock(self->lock);
+        PyThread_free_lock(self->lock);
+    }
+    Py_XDECREF(self->lst);
+    if (self->weakreflist != NULL)
+        PyObject_ClearWeakRefs((PyObject *) self);
+    Py_TYPE(self)->tp_free(self);
+}
+
+static int
+simplequeue_traverse(simplequeueobject *self, visitproc visit, void *arg)
+{
+    Py_VISIT(self->lst);
+    return 0;
+}
+
+/*[clinic input]
+@classmethod
+_queue.SimpleQueue.__new__ as simplequeue_new
+
+Simple, unbounded, reentrant FIFO queue.
+[clinic start generated code]*/
+
+static PyObject *
+simplequeue_new_impl(PyTypeObject *type)
+/*[clinic end generated code: output=ba97740608ba31cd input=a0674a1643e3e2fb]*/
+{
+    simplequeueobject *self;
+
+    self = (simplequeueobject *) type->tp_alloc(type, 0);
+    if (self != NULL) {
+        self->weakreflist = NULL;
+        self->lst = PyList_New(0);
+        self->lock = PyThread_allocate_lock();
+        self->lst_pos = 0;
+        if (self->lock == NULL) {
+            Py_DECREF(self);
+            PyErr_SetString(PyExc_MemoryError, "can't allocate lock");
+            return NULL;
+        }
+        if (self->lst == NULL) {
+            Py_DECREF(self);
+            return NULL;
+        }
+    }
+
+    return (PyObject *) self;
+}
+
+/*[clinic input]
+_queue.SimpleQueue.put
+    item: object
+    block: bool = True
+    timeout: object = None
+
+Put the item on the queue.
+
+The optional 'block' and 'timeout' arguments are ignored, as this method
+never blocks.  They are provided for compatibility with the Queue class.
+
+[clinic start generated code]*/
+
+static PyObject *
+_queue_SimpleQueue_put_impl(simplequeueobject *self, PyObject *item,
+                            int block, PyObject *timeout)
+/*[clinic end generated code: output=4333136e88f90d8b input=6e601fa707a782d5]*/
+{
+    /* BEGIN GIL-protected critical section */
+    if (PyList_Append(self->lst, item) < 0)
+        return NULL;
+    if (self->locked) {
+        /* A get() may be waiting, wake it up */
+        self->locked = 0;
+        PyThread_release_lock(self->lock);
+    }
+    /* END GIL-protected critical section */
+    Py_RETURN_NONE;
+}
+
+/*[clinic input]
+_queue.SimpleQueue.put_nowait
+    item: object
+
+Put an item into the queue without blocking.
+
+This is exactly equivalent to `put(item)` and is only provided
+for compatibility with the Queue class.
+
+[clinic start generated code]*/
+
+static PyObject *
+_queue_SimpleQueue_put_nowait_impl(simplequeueobject *self, PyObject *item)
+/*[clinic end generated code: output=0990536715efb1f1 input=36b1ea96756b2ece]*/
+{
+    return _queue_SimpleQueue_put_impl(self, item, 0, Py_None);
+}
+
+static PyObject *
+simplequeue_pop_item(simplequeueobject *self)
+{
+    Py_ssize_t count, n;
+    PyObject *item;
+
+    n = PyList_GET_SIZE(self->lst);
+    assert(self->lst_pos < n);
+
+    item = PyList_GET_ITEM(self->lst, self->lst_pos);
+    Py_INCREF(Py_None);
+    PyList_SET_ITEM(self->lst, self->lst_pos, Py_None);
+    self->lst_pos += 1;
+    count = n - self->lst_pos;
+    if (self->lst_pos > count) {
+        /* The list is more than 50% empty, reclaim space at the beginning */
+        if (PyList_SetSlice(self->lst, 0, self->lst_pos, NULL)) {
+            /* Undo pop */
+            self->lst_pos -= 1;
+            PyList_SET_ITEM(self->lst, self->lst_pos, item);
+            return NULL;
+        }
+        self->lst_pos = 0;
+    }
+    return item;
+}
+
+/*[clinic input]
+_queue.SimpleQueue.get
+    block: bool = True
+    timeout: object = None
+
+Remove and return an item from the queue.
+
+If optional args 'block' is true and 'timeout' is None (the default),
+block if necessary until an item is available. If 'timeout' is
+a non-negative number, it blocks at most 'timeout' seconds and raises
+the Empty exception if no item was available within that time.
+Otherwise ('block' is false), return an item if one is immediately
+available, else raise the Empty exception ('timeout' is ignored
+in that case).
+
+[clinic start generated code]*/
+
+static PyObject *
+_queue_SimpleQueue_get_impl(simplequeueobject *self, int block,
+                            PyObject *timeout)
+/*[clinic end generated code: output=ec82a7157dcccd1a input=4bf691f9f01fa297]*/
+{
+    _PyTime_t endtime = 0;
+    _PyTime_t timeout_val;
+    PyObject *item;
+    PyLockStatus r;
+    PY_TIMEOUT_T microseconds;
+
+    if (block == 0) {
+        /* Non-blocking */
+        microseconds = 0;
+    }
+    else if (timeout != Py_None) {
+        /* With timeout */
+        if (_PyTime_FromSecondsObject(&timeout_val,
+                                      timeout, _PyTime_ROUND_CEILING) < 0)
+            return NULL;
+        if (timeout_val < 0) {
+            PyErr_SetString(PyExc_ValueError,
+                            "'timeout' must be a non-negative number");
+            return NULL;
+        }
+        microseconds = _PyTime_AsMicroseconds(timeout_val,
+                                              _PyTime_ROUND_CEILING);
+        if (microseconds >= PY_TIMEOUT_MAX) {
+            PyErr_SetString(PyExc_OverflowError,
+                            "timeout value is too large");
+            return NULL;
+        }
+        endtime = _PyTime_GetMonotonicClock() + timeout_val;
+    }
+    else {
+        /* Infinitely blocking */
+        microseconds = -1;
+    }
+
+    /* put() signals the queue to be non-empty by releasing the lock.
+     * So we simply try to acquire the lock in a loop, until the condition
+     * (queue non-empty) becomes true.
+     */
+    while (self->lst_pos == PyList_GET_SIZE(self->lst)) {
+        /* First a simple non-blocking try without releasing the GIL */
+        r = PyThread_acquire_lock_timed(self->lock, 0, 0);
+        if (r == PY_LOCK_FAILURE && microseconds != 0) {
+            Py_BEGIN_ALLOW_THREADS
+            r = PyThread_acquire_lock_timed(self->lock, microseconds, 1);
+            Py_END_ALLOW_THREADS
+        }
+        if (r == PY_LOCK_INTR && Py_MakePendingCalls() < 0) {
+            return NULL;
+        }
+        if (r == PY_LOCK_FAILURE) {
+            /* Timed out */
+            PyErr_SetNone(EmptyError);
+            return NULL;
+        }
+        self->locked = 1;
+        /* Adjust timeout for next iteration (if any) */
+        if (endtime > 0) {
+            timeout_val = endtime - _PyTime_GetMonotonicClock();
+            microseconds = _PyTime_AsMicroseconds(timeout_val, _PyTime_ROUND_CEILING);
+        }
+    }
+    /* BEGIN GIL-protected critical section */
+    assert(self->lst_pos < PyList_GET_SIZE(self->lst));
+    item = simplequeue_pop_item(self);
+    if (self->locked) {
+        PyThread_release_lock(self->lock);
+        self->locked = 0;
+    }
+    /* END GIL-protected critical section */
+
+    return item;
+}
+
+/*[clinic input]
+_queue.SimpleQueue.get_nowait
+
+Remove and return an item from the queue without blocking.
+
+Only get an item if one is immediately available. Otherwise
+raise the Empty exception.
+[clinic start generated code]*/
+
+static PyObject *
+_queue_SimpleQueue_get_nowait_impl(simplequeueobject *self)
+/*[clinic end generated code: output=a89731a75dbe4937 input=6fe5102db540a1b9]*/
+{
+    return _queue_SimpleQueue_get_impl(self, 0, Py_None);
+}
+
+/*[clinic input]
+_queue.SimpleQueue.empty -> bool
+
+Return True if the queue is empty, False otherwise (not reliable!).
+[clinic start generated code]*/
+
+static int
+_queue_SimpleQueue_empty_impl(simplequeueobject *self)
+/*[clinic end generated code: output=1a02a1b87c0ef838 input=1a98431c45fd66f9]*/
+{
+    return self->lst_pos == PyList_GET_SIZE(self->lst);
+}
+
+/*[clinic input]
+_queue.SimpleQueue.qsize -> Py_ssize_t
+
+Return the approximate size of the queue (not reliable!).
+[clinic start generated code]*/
+
+static Py_ssize_t
+_queue_SimpleQueue_qsize_impl(simplequeueobject *self)
+/*[clinic end generated code: output=f9dcd9d0a90e121e input=7a74852b407868a1]*/
+{
+    return PyList_GET_SIZE(self->lst) - self->lst_pos;
+}
+
+
+#include "clinic/_queuemodule.c.h"
+
+
+static PyMethodDef simplequeue_methods[] = {
+    _QUEUE_SIMPLEQUEUE_EMPTY_METHODDEF
+    _QUEUE_SIMPLEQUEUE_GET_METHODDEF
+    _QUEUE_SIMPLEQUEUE_GET_NOWAIT_METHODDEF
+    _QUEUE_SIMPLEQUEUE_PUT_METHODDEF
+    _QUEUE_SIMPLEQUEUE_PUT_NOWAIT_METHODDEF
+    _QUEUE_SIMPLEQUEUE_QSIZE_METHODDEF
+    {NULL,           NULL}              /* sentinel */
+};
+
+
+PyTypeObject PySimpleQueueType = {
+    PyVarObject_HEAD_INIT(NULL, 0)
+    "_queue.SimpleQueue",               /*tp_name*/
+    sizeof(simplequeueobject),          /*tp_size*/
+    0,                                  /*tp_itemsize*/
+    /* methods */
+    (destructor)simplequeue_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 | Py_TPFLAGS_BASETYPE
+        | Py_TPFLAGS_HAVE_GC,           /* tp_flags */
+    simplequeue_new__doc__,             /*tp_doc*/
+    (traverseproc)simplequeue_traverse, /*tp_traverse*/
+    0,                                  /*tp_clear*/
+    0,                                  /*tp_richcompare*/
+    offsetof(simplequeueobject, weakreflist), /*tp_weaklistoffset*/
+    0,                                  /*tp_iter*/
+    0,                                  /*tp_iternext*/
+    simplequeue_methods,                /*tp_methods*/
+    0,                                  /* tp_members */
+    0,                                  /* tp_getset */
+    0,                                  /* tp_base */
+    0,                                  /* tp_dict */
+    0,                                  /* tp_descr_get */
+    0,                                  /* tp_descr_set */
+    0,                                  /* tp_dictoffset */
+    0,                                  /* tp_init */
+    0,                                  /* tp_alloc */
+    simplequeue_new                     /* tp_new */
+};
+
+
+/* Initialization function */
+
+PyDoc_STRVAR(queue_module_doc,
+"C implementation of the Python queue module.\n\
+This module is an implementation detail, please do not use it directly.");
+
+static struct PyModuleDef queuemodule = {
+    PyModuleDef_HEAD_INIT,
+    "_queue",
+    queue_module_doc,
+    -1,
+    NULL,
+    NULL,
+    NULL,
+    NULL,
+    NULL
+};
+
+
+PyMODINIT_FUNC
+PyInit__queue(void)
+{
+    PyObject *m;
+
+    /* Create the module */
+    m = PyModule_Create(&queuemodule);
+    if (m == NULL)
+        return NULL;
+
+    EmptyError = PyErr_NewExceptionWithDoc(
+        "_queue.Empty",
+        "Exception raised by Queue.get(block=0)/get_nowait().",
+        NULL, NULL);
+    if (EmptyError == NULL)
+        return NULL;
+
+    Py_INCREF(EmptyError);
+    if (PyModule_AddObject(m, "Empty", EmptyError) < 0)
+        return NULL;
+
+    if (PyType_Ready(&PySimpleQueueType) < 0)
+        return NULL;
+    Py_INCREF(&PySimpleQueueType);
+    if (PyModule_AddObject(m, "SimpleQueue", (PyObject *)&PySimpleQueueType) < 0)
+        return NULL;
+
+    return m;
+}

Modules/clinic/_queuemodule.c.h

@@ -0,0 +1,218 @@
+/*[clinic input]
+preserve
+[clinic start generated code]*/
+
+PyDoc_STRVAR(simplequeue_new__doc__,
+"SimpleQueue()\n"
+"--\n"
+"\n"
+"Simple, unbounded, reentrant FIFO queue.");
+
+static PyObject *
+simplequeue_new_impl(PyTypeObject *type);
+
+static PyObject *
+simplequeue_new(PyTypeObject *type, PyObject *args, PyObject *kwargs)
+{
+    PyObject *return_value = NULL;
+
+    if ((type == &PySimpleQueueType) &&
+        !_PyArg_NoPositional("SimpleQueue", args)) {
+        goto exit;
+    }
+    if ((type == &PySimpleQueueType) &&
+        !_PyArg_NoKeywords("SimpleQueue", kwargs)) {
+        goto exit;
+    }
+    return_value = simplequeue_new_impl(type);
+
+exit:
+    return return_value;
+}
+
+PyDoc_STRVAR(_queue_SimpleQueue_put__doc__,
+"put($self, /, item, block=True, timeout=None)\n"
+"--\n"
+"\n"
+"Put the item on the queue.\n"
+"\n"
+"The optional \'block\' and \'timeout\' arguments are ignored, as this method\n"
+"never blocks.  They are provided for compatibility with the Queue class.");
+
+#define _QUEUE_SIMPLEQUEUE_PUT_METHODDEF    \
+    {"put", (PyCFunction)_queue_SimpleQueue_put, METH_FASTCALL|METH_KEYWORDS, _queue_SimpleQueue_put__doc__},
+
+static PyObject *
+_queue_SimpleQueue_put_impl(simplequeueobject *self, PyObject *item,
+                            int block, PyObject *timeout);
+
+static PyObject *
+_queue_SimpleQueue_put(simplequeueobject *self, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
+{
+    PyObject *return_value = NULL;
+    static const char * const _keywords[] = {"item", "block", "timeout", NULL};
+    static _PyArg_Parser _parser = {"O|pO:put", _keywords, 0};
+    PyObject *item;
+    int block = 1;
+    PyObject *timeout = Py_None;
+
+    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
+        &item, &block, &timeout)) {
+        goto exit;
+    }
+    return_value = _queue_SimpleQueue_put_impl(self, item, block, timeout);
+
+exit:
+    return return_value;
+}
+
+PyDoc_STRVAR(_queue_SimpleQueue_put_nowait__doc__,
+"put_nowait($self, /, item)\n"
+"--\n"
+"\n"
+"Put an item into the queue without blocking.\n"
+"\n"
+"This is exactly equivalent to `put(item)` and is only provided\n"
+"for compatibility with the Queue class.");
+
+#define _QUEUE_SIMPLEQUEUE_PUT_NOWAIT_METHODDEF    \
+    {"put_nowait", (PyCFunction)_queue_SimpleQueue_put_nowait, METH_FASTCALL|METH_KEYWORDS, _queue_SimpleQueue_put_nowait__doc__},
+
+static PyObject *
+_queue_SimpleQueue_put_nowait_impl(simplequeueobject *self, PyObject *item);
+
+static PyObject *
+_queue_SimpleQueue_put_nowait(simplequeueobject *self, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
+{
+    PyObject *return_value = NULL;
+    static const char * const _keywords[] = {"item", NULL};
+    static _PyArg_Parser _parser = {"O:put_nowait", _keywords, 0};
+    PyObject *item;
+
+    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
+        &item)) {
+        goto exit;
+    }
+    return_value = _queue_SimpleQueue_put_nowait_impl(self, item);
+
+exit:
+    return return_value;
+}
+
+PyDoc_STRVAR(_queue_SimpleQueue_get__doc__,
+"get($self, /, block=True, timeout=None)\n"
+"--\n"
+"\n"
+"Remove and return an item from the queue.\n"
+"\n"
+"If optional args \'block\' is true and \'timeout\' is None (the default),\n"
+"block if necessary until an item is available. If \'timeout\' is\n"
+"a non-negative number, it blocks at most \'timeout\' seconds and raises\n"
+"the Empty exception if no item was available within that time.\n"
+"Otherwise (\'block\' is false), return an item if one is immediately\n"
+"available, else raise the Empty exception (\'timeout\' is ignored\n"
+"in that case).");
+
+#define _QUEUE_SIMPLEQUEUE_GET_METHODDEF    \
+    {"get", (PyCFunction)_queue_SimpleQueue_get, METH_FASTCALL|METH_KEYWORDS, _queue_SimpleQueue_get__doc__},
+
+static PyObject *
+_queue_SimpleQueue_get_impl(simplequeueobject *self, int block,
+                            PyObject *timeout);
+
+static PyObject *
+_queue_SimpleQueue_get(simplequeueobject *self, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
+{
+    PyObject *return_value = NULL;
+    static const char * const _keywords[] = {"block", "timeout", NULL};
+    static _PyArg_Parser _parser = {"|pO:get", _keywords, 0};
+    int block = 1;
+    PyObject *timeout = Py_None;
+
+    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
+        &block, &timeout)) {
+        goto exit;
+    }
+    return_value = _queue_SimpleQueue_get_impl(self, block, timeout);
+
+exit:
+    return return_value;
+}
+
+PyDoc_STRVAR(_queue_SimpleQueue_get_nowait__doc__,
+"get_nowait($self, /)\n"
+"--\n"
+"\n"
+"Remove and return an item from the queue without blocking.\n"
+"\n"
+"Only get an item if one is immediately available. Otherwise\n"
+"raise the Empty exception.");
+
+#define _QUEUE_SIMPLEQUEUE_GET_NOWAIT_METHODDEF    \
+    {"get_nowait", (PyCFunction)_queue_SimpleQueue_get_nowait, METH_NOARGS, _queue_SimpleQueue_get_nowait__doc__},
+
+static PyObject *
+_queue_SimpleQueue_get_nowait_impl(simplequeueobject *self);
+
+static PyObject *
+_queue_SimpleQueue_get_nowait(simplequeueobject *self, PyObject *Py_UNUSED(ignored))
+{
+    return _queue_SimpleQueue_get_nowait_impl(self);
+}
+
+PyDoc_STRVAR(_queue_SimpleQueue_empty__doc__,
+"empty($self, /)\n"
+"--\n"
+"\n"
+"Return True if the queue is empty, False otherwise (not reliable!).");
+
+#define _QUEUE_SIMPLEQUEUE_EMPTY_METHODDEF    \
+    {"empty", (PyCFunction)_queue_SimpleQueue_empty, METH_NOARGS, _queue_SimpleQueue_empty__doc__},
+
+static int
+_queue_SimpleQueue_empty_impl(simplequeueobject *self);
+
+static PyObject *
+_queue_SimpleQueue_empty(simplequeueobject *self, PyObject *Py_UNUSED(ignored))
+{
+    PyObject *return_value = NULL;
+    int _return_value;
+
+    _return_value = _queue_SimpleQueue_empty_impl(self);
+    if ((_return_value == -1) && PyErr_Occurred()) {
+        goto exit;
+    }
+    return_value = PyBool_FromLong((long)_return_value);
+
+exit:
+    return return_value;
+}
+
+PyDoc_STRVAR(_queue_SimpleQueue_qsize__doc__,
+"qsize($self, /)\n"
+"--\n"
+"\n"
+"Return the approximate size of the queue (not reliable!).");
+
+#define _QUEUE_SIMPLEQUEUE_QSIZE_METHODDEF    \
+    {"qsize", (PyCFunction)_queue_SimpleQueue_qsize, METH_NOARGS, _queue_SimpleQueue_qsize__doc__},
+
+static Py_ssize_t
+_queue_SimpleQueue_qsize_impl(simplequeueobject *self);
+
+static PyObject *
+_queue_SimpleQueue_qsize(simplequeueobject *self, PyObject *Py_UNUSED(ignored))
+{
+    PyObject *return_value = NULL;
+    Py_ssize_t _return_value;
+
+    _return_value = _queue_SimpleQueue_qsize_impl(self);
+    if ((_return_value == -1) && PyErr_Occurred()) {
+        goto exit;
+    }
+    return_value = PyLong_FromSsize_t(_return_value);
+
+exit:
+    return return_value;
+}
+/*[clinic end generated code: output=8badc3bb85263689 input=a9049054013a1b77]*/

PCbuild/_queue.vcxproj

@@ -0,0 +1,77 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project DefaultTargets="Build" ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <ItemGroup Label="ProjectConfigurations">
+    <ProjectConfiguration Include="Debug|Win32">
+      <Configuration>Debug</Configuration>
+      <Platform>Win32</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Debug|x64">
+      <Configuration>Debug</Configuration>
+      <Platform>x64</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="PGInstrument|Win32">
+      <Configuration>PGInstrument</Configuration>
+      <Platform>Win32</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="PGInstrument|x64">
+      <Configuration>PGInstrument</Configuration>
+      <Platform>x64</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="PGUpdate|Win32">
+      <Configuration>PGUpdate</Configuration>
+      <Platform>Win32</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="PGUpdate|x64">
+      <Configuration>PGUpdate</Configuration>
+      <Platform>x64</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Release|Win32">
+      <Configuration>Release</Configuration>
+      <Platform>Win32</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Release|x64">
+      <Configuration>Release</Configuration>
+      <Platform>x64</Platform>
+    </ProjectConfiguration>
+  </ItemGroup>
+  <PropertyGroup Label="Globals">
+    <ProjectGuid>{78D80A15-BD8C-44E2-B49E-1F05B0A0A687}</ProjectGuid>
+    <RootNamespace>_queue</RootNamespace>
+    <Keyword>Win32Proj</Keyword>
+  </PropertyGroup>
+  <Import Project="python.props" />
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.Default.props" />
+  <PropertyGroup Label="Configuration">
+    <ConfigurationType>DynamicLibrary</ConfigurationType>
+    <CharacterSet>NotSet</CharacterSet>
+  </PropertyGroup>
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.props" />
+  <PropertyGroup>
+    <TargetExt>.pyd</TargetExt>
+  </PropertyGroup>
+  <ImportGroup Label="ExtensionSettings">
+  </ImportGroup>
+  <ImportGroup Label="PropertySheets">
+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+    <Import Project="pyproject.props" />
+  </ImportGroup>
+  <PropertyGroup Label="UserMacros" />
+  <PropertyGroup>
+    <_ProjectFileVersion>10.0.30319.1</_ProjectFileVersion>
+  </PropertyGroup>
+  <ItemGroup>
+    <ClCompile Include="..\Modules\_queuemodule.c" />
+  </ItemGroup>
+  <ItemGroup>
+    <ResourceCompile Include="..\PC\python_nt.rc" />
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="pythoncore.vcxproj">
+      <Project>{cf7ac3d1-e2df-41d2-bea6-1e2556cdea26}</Project>
+      <ReferenceOutputAssembly>false</ReferenceOutputAssembly>
+    </ProjectReference>
+  </ItemGroup>
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
+  <ImportGroup Label="ExtensionTargets">
+  </ImportGroup>
+</Project>

PCbuild/_queue.vcxproj.filters

@@ -0,0 +1,16 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <ItemGroup>
+    <ResourceCompile Include="..\PC\python_nt.rc" />
+  </ItemGroup>
+  <ItemGroup>
+    <Filter Include="Source Files">
+      <UniqueIdentifier>{c56a5dd3-7838-48e9-a781-855d8be7370f}</UniqueIdentifier>
+    </Filter>
+  </ItemGroup>
+  <ItemGroup>
+    <ClCompile Include="..\Modules\_queuemodule.c">
+      <Filter>Source Files</Filter>
+    </ClCompile>
+  </ItemGroup>
+</Project>

PCbuild/pcbuild.proj

@@ -49,7 +49,7 @@
     <!-- pyshellext.dll -->
     <Projects Include="pyshellext.vcxproj" />
     <!-- Extension modules -->
-    <ExtensionModules Include="_asyncio;_ctypes;_decimal;_elementtree;_msi;_multiprocessing;_overlapped;pyexpat;select;unicodedata;winsound" />
+    <ExtensionModules Include="_asyncio;_ctypes;_decimal;_elementtree;_msi;_multiprocessing;_overlapped;pyexpat;_queue;select;unicodedata;winsound" />
     <!-- Extension modules that require external sources -->
     <ExternalModules Include="_bz2;_lzma;_sqlite3" />
     <!-- _ssl will build _socket as well, which may cause conflicts in parallel builds -->

PCbuild/pcbuild.sln

@@ -89,6 +89,8 @@ Project("{8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942}") = "_testconsole", "_testconsol
 EndProject
 Project("{8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942}") = "_asyncio", "_asyncio.vcxproj", "{384C224A-7474-476E-A01B-750EA7DE918C}"
 EndProject
+Project("{8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942}") = "_queue", "_queue.vcxproj", "{78D80A15-BD8C-44E2-B49E-1F05B0A0A687}"
+EndProject
 Project("{8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942}") = "liblzma", "liblzma.vcxproj", "{12728250-16EC-4DC6-94D7-E21DD88947F8}"
 EndProject
 Global
@@ -659,6 +661,22 @@ Global
 		{384C224A-7474-476E-A01B-750EA7DE918C}.Release|Win32.Build.0 = Release|Win32
 		{384C224A-7474-476E-A01B-750EA7DE918C}.Release|x64.ActiveCfg = Release|x64
 		{384C224A-7474-476E-A01B-750EA7DE918C}.Release|x64.Build.0 = Release|x64
+		{78D80A15-BD8C-44E2-B49E-1F05B0A0A687}.Debug|Win32.ActiveCfg = Debug|Win32
+		{78D80A15-BD8C-44E2-B49E-1F05B0A0A687}.Debug|Win32.Build.0 = Debug|Win32
+		{78D80A15-BD8C-44E2-B49E-1F05B0A0A687}.Debug|x64.ActiveCfg = Debug|x64
+		{78D80A15-BD8C-44E2-B49E-1F05B0A0A687}.Debug|x64.Build.0 = Debug|x64
+		{78D80A15-BD8C-44E2-B49E-1F05B0A0A687}.PGInstrument|Win32.ActiveCfg = PGInstrument|Win32
+		{78D80A15-BD8C-44E2-B49E-1F05B0A0A687}.PGInstrument|Win32.Build.0 = PGInstrument|Win32
+		{78D80A15-BD8C-44E2-B49E-1F05B0A0A687}.PGInstrument|x64.ActiveCfg = PGInstrument|x64
+		{78D80A15-BD8C-44E2-B49E-1F05B0A0A687}.PGInstrument|x64.Build.0 = PGInstrument|x64
+		{78D80A15-BD8C-44E2-B49E-1F05B0A0A687}.PGUpdate|Win32.ActiveCfg = PGUpdate|Win32
+		{78D80A15-BD8C-44E2-B49E-1F05B0A0A687}.PGUpdate|Win32.Build.0 = PGUpdate|Win32
+		{78D80A15-BD8C-44E2-B49E-1F05B0A0A687}.PGUpdate|x64.ActiveCfg = PGUpdate|x64
+		{78D80A15-BD8C-44E2-B49E-1F05B0A0A687}.PGUpdate|x64.Build.0 = PGUpdate|x64
+		{78D80A15-BD8C-44E2-B49E-1F05B0A0A687}.Release|Win32.ActiveCfg = Release|Win32
+		{78D80A15-BD8C-44E2-B49E-1F05B0A0A687}.Release|Win32.Build.0 = Release|Win32
+		{78D80A15-BD8C-44E2-B49E-1F05B0A0A687}.Release|x64.ActiveCfg = Release|x64
+		{78D80A15-BD8C-44E2-B49E-1F05B0A0A687}.Release|x64.Build.0 = Release|x64
 		{12728250-16EC-4DC6-94D7-E21DD88947F8}.Debug|Win32.ActiveCfg = Debug|Win32
 		{12728250-16EC-4DC6-94D7-E21DD88947F8}.Debug|Win32.Build.0 = Debug|Win32
 		{12728250-16EC-4DC6-94D7-E21DD88947F8}.Debug|x64.ActiveCfg = Debug|x64

PCbuild/pythoncore.vcxproj.filters

@@ -506,6 +506,9 @@
     <ClCompile Include="..\Modules\_pickle.c">
       <Filter>Modules</Filter>
     </ClCompile>
+    <ClCompile Include="..\Modules\_queuemodule.c">
+      <Filter>Modules</Filter>
+    </ClCompile>
     <ClCompile Include="..\Modules\_randommodule.c">
       <Filter>Modules</Filter>
     </ClCompile>

setup.py

@@ -699,6 +699,8 @@ def detect_modules(self):
         exts.append( Extension('_opcode', ['_opcode.c']) )
         # asyncio speedups
         exts.append( Extension("_asyncio", ["_asynciomodule.c"]) )
+        # _queue module
+        exts.append( Extension("_queue", ["_queuemodule.c"]) )
 
         # Modules with some UNIX dependencies -- on by default:
         # (If you have a really backward UNIX, select and socket may not be