Add asyncio queue shutdown

EpicWink · EpicWink · commit 440a7024ff65 · 2023-05-06T14:50:35.000+10:00
* Include docs
diff --git a/Doc/library/asyncio-queue.rst b/Doc/library/asyncio-queue.rst
@@ -62,6 +62,9 @@ Queue
       Remove and return an item from the queue. If queue is empty,
       wait until an item is available.
 
+      Raises :exc:`QueueShutDown` if the queue has been shut down and
+      is empty, or if the queue has been shut down immediately.
+
    .. method:: get_nowait()
 
       Return an item if one is immediately available, else raise
@@ -77,11 +80,16 @@ Queue
       work on it is complete.  When the count of unfinished tasks drops
       to zero, :meth:`join` unblocks.
 
+      Raises :exc:`QueueShutDown` if the queue has been shut down
+      immediately.
+
    .. coroutinemethod:: put(item)
 
       Put an item into the queue. If the queue is full, wait until a
       free slot is available before adding the item.
 
+      Raises :exc:`QueueShutDown` if the queue has been shut down.
+
    .. method:: put_nowait(item)
 
       Put an item into the queue without blocking.
@@ -92,6 +100,19 @@ Queue
 
       Return the number of items in the queue.
 
+   .. method:: shutdown(immediate=False)
+
+      Shut-down the queue, making queue gets and puts raise
+      :exc:`QueueShutDown`.
+
+      By default, gets will only raise once the queue is empty. Set
+      *immediate* to true to make gets raise immediately instead.
+
+      All blocked callers of put() will be unblocked, and also get()
+      and join() if *immediate* is true.
+
+      .. versionadded:: 3.12
+
    .. method:: task_done()
 
       Indicate that a formerly enqueued task is complete.
@@ -108,6 +129,9 @@ Queue
       Raises :exc:`ValueError` if called more times than there were
       items placed in the queue.
 
+      Raises :exc:`QueueShutDown` if the queue has been shut down
+      immediately.
+
 
 Priority Queue
 ==============
@@ -145,6 +169,14 @@ Exceptions
    on a queue that has reached its *maxsize*.
 
 
+.. exception:: QueueShutDown
+
+   Exception raised when getting an item from or putting an item onto a
+   queue which has been shut down.
+
+   .. versionadded:: 3.12
+
+
 Examples
 ========
 
diff --git a/Lib/asyncio/queues.py b/Lib/asyncio/queues.py
@@ -1,4 +1,11 @@
-__all__ = ('Queue', 'PriorityQueue', 'LifoQueue', 'QueueFull', 'QueueEmpty')
+__all__ = (
+    'Queue',
+    'PriorityQueue',
+    'LifoQueue',
+    'QueueFull',
+    'QueueEmpty',
+    'QueueShutDown',
+)
 
 import collections
 import heapq
@@ -18,6 +25,16 @@ class QueueFull(Exception):
     pass
 
 
+class QueueShutDown(Exception):
+    """Raised when putting on to or getting from a shut-down Queue."""
+    pass
+
+
+_queue_alive = "alive"
+_queue_shutdown = "shutdown"
+_queue_shutdown_immediate = "shutdown-immediate"
+
+
 class Queue(mixins._LoopBoundMixin):
     """A queue, useful for coordinating producer and consumer coroutines.
 
@@ -41,6 +58,7 @@ def __init__(self, maxsize=0):
         self._finished = locks.Event()
         self._finished.set()
         self._init(maxsize)
+        self.shutdown_state = _queue_alive
 
     # These three are overridable in subclasses.
 
@@ -113,6 +131,8 @@ async def put(self, item):
         Put an item into the queue. If the queue is full, wait until a free
         slot is available before adding item.
         """
+        if self.shutdown_state != _queue_alive:
+            raise QueueShutDown
         while self.full():
             putter = self._get_loop().create_future()
             self._putters.append(putter)
@@ -132,13 +152,17 @@ async def put(self, item):
                     # the call.  Wake up the next in line.
                     self._wakeup_next(self._putters)
                 raise
+            if self.shutdown_state != _queue_alive:
+                raise QueueShutDown
         return self.put_nowait(item)
 
     def put_nowait(self, item):
         """Put an item into the queue without blocking.
 
         If no free slot is immediately available, raise QueueFull.
         """
+        if self.shutdown_state != _queue_alive:
+            raise QueueShutDown
         if self.full():
             raise QueueFull
         self._put(item)
@@ -151,7 +175,11 @@ async def get(self):
 
         If queue is empty, wait until an item is available.
         """
+        if self.shutdown_state == _queue_shutdown_immediate:
+            raise QueueShutDown
         while self.empty():
+            if self.shutdown_state != _queue_alive:
+                raise QueueShutDown
             getter = self._get_loop().create_future()
             self._getters.append(getter)
             try:
@@ -170,6 +198,8 @@ async def get(self):
                     # the call.  Wake up the next in line.
                     self._wakeup_next(self._getters)
                 raise
+            if self.shutdown_state == _queue_shutdown_immediate:
+                raise QueueShutDown
         return self.get_nowait()
 
     def get_nowait(self):
@@ -178,7 +208,11 @@ def get_nowait(self):
         Return an item if one is immediately available, else raise QueueEmpty.
         """
         if self.empty():
+            if self.shutdown_state != _queue_alive:
+                raise QueueShutDown
             raise QueueEmpty
+        elif self.shutdown_state == _queue_shutdown_immediate:
+            raise QueueShutDown
         item = self._get()
         self._wakeup_next(self._putters)
         return item
@@ -214,6 +248,27 @@ async def join(self):
         if self._unfinished_tasks > 0:
             await self._finished.wait()
 
+    def shutdown(self, immediate=False):
+        """Shut-down the queue, making queue gets and puts raise.
+
+        By default, gets will only raise once the queue is empty. Set
+        'immediate' to True to make gets raise immediately instead.
+
+        All blocked callers of put() will be unblocked, and also get()
+        and join() if 'immediate'. The QueueShutDown exception is raised.
+        """
+        if immediate:
+            self.shutdown_state = _queue_shutdown_immediate
+            while self._getters:
+                getter = self._getters.popleft()
+                if not getter.done():
+                    getter.set_result(None)
+        else:
+            self.shutdown_state = _queue_shutdown
+        while self._putters:
+            putter = self._putters.popleft()
+            if not putter.done():
+                putter.set_result(None)
 
 class PriorityQueue(Queue):
     """A subclass of Queue; retrieves entries in priority order (lowest first).
diff --git a/Lib/test/test_asyncio/test_queues.py b/Lib/test/test_asyncio/test_queues.py
@@ -522,5 +522,62 @@ class PriorityQueueJoinTests(_QueueJoinTestMixin, unittest.IsolatedAsyncioTestCa
     q_class = asyncio.PriorityQueue
 
 
+class _QueueShutdownTestMixin:
+    q_class = None
+
+    async def test_empty(self):
+        q = self.q_class()
+        q.shutdown()
+        try:
+            await q.put("data")
+            self.fail("Didn't appear to shut-down queue")
+        except asyncio.QueueShutDown:
+            pass
+        try:
+            await q.get()
+            self.fail("Didn't appear to shut-down queue")
+        except asyncio.QueueShutDown:
+            pass
+
+    async def test_nonempty(self):
+        q = self.q_class()
+        q.put_nowait("data")
+        q.shutdown()
+        await q.get()
+        try:
+            await q.get()
+            self.fail("Didn't appear to shut-down queue")
+        except asyncio.QueueShutDown:
+            pass
+
+    async def test_immediate(self):
+        q = self.q_class()
+        q.put_nowait("data")
+        q.shutdown(immediate=True)
+        try:
+            await q.get()
+            self.fail("Didn't appear to shut-down queue")
+        except asyncio.QueueShutDown:
+            pass
+
+
+class QueueShutdownTests(
+    _QueueShutdownTestMixin, unittest.IsolatedAsyncioTestCase
+):
+    q_class = asyncio.Queue
+
+
+class LifoQueueShutdownTests(
+    _QueueShutdownTestMixin, unittest.IsolatedAsyncioTestCase
+):
+    q_class = asyncio.LifoQueue
+
+
+class PriorityQueueShutdownTests(
+    _QueueShutdownTestMixin, unittest.IsolatedAsyncioTestCase
+):
+    q_class = asyncio.PriorityQueue
+
+
 if __name__ == '__main__':
     unittest.main()
