gh-96471: Add asyncio queue shutdown

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 +100,21 @@ Queue
 
       Return the number of items in the queue.
 
+   .. method:: shutdown(immediate=False)
+
+      Shut down the queue, making :meth:`~Queue.get` and :meth:`~Queue.put`
+      raise :exc:`QueueShutDown`.
+
+      By default, :meth:`~Queue.get` on a shut down queue will only raise once
+      the queue is empty. Set *immediate* to true to make gets raise
+      immediately instead.
+
+      All blocked callers of :meth:`~Queue.put` will be unblocked. If
+      *immediate* is true, also unblock callers of :meth:`~Queue.get` and
+      :meth:`~Queue.join`.
+
+      .. versionadded:: 3.13
+
    .. method:: task_done()
 
       Indicate that a formerly enqueued task is complete.
@@ -108,6 +131,9 @@ 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 +171,14 @@ 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:: 3.13
+
+
 Examples
 ========
 

Lib/asyncio/queues.py

@@ -1,6 +1,14 @@
-__all__ = ('Queue', 'PriorityQueue', 'LifoQueue', 'QueueFull', 'QueueEmpty')
+__all__ = (
+    'Queue',
+    'PriorityQueue',
+    'LifoQueue',
+    'QueueFull',
+    'QueueEmpty',
+    'QueueShutDown',
+)
 
 import collections
+import enum
 import heapq
 from types import GenericAlias
 
@@ -18,6 +26,17 @@ class QueueFull(Exception):
     pass
 
 
+class QueueShutDown(Exception):
+    """Raised when putting on to or getting from a shut-down Queue."""
+    pass
+
+
+class _QueueState(enum.Enum):
+    ALIVE = "alive"
+    SHUTDOWN = "shutdown"
+    SHUTDOWN_IMMEDIATE = "shutdown-immediate"
+
+
 class Queue(mixins._LoopBoundMixin):
     """A queue, useful for coordinating producer and consumer coroutines.
 
@@ -41,6 +60,7 @@ def __init__(self, maxsize=0):
         self._finished = locks.Event()
         self._finished.set()
         self._init(maxsize)
+        self._shutdown_state = _QueueState.ALIVE
 
     # These three are overridable in subclasses.
 
@@ -81,6 +101,8 @@ def _format(self):
             result += f' _putters[{len(self._putters)}]'
         if self._unfinished_tasks:
             result += f' tasks={self._unfinished_tasks}'
+        if not self._is_alive():
+            result += f' state={self._shutdown_state.value}'
         return result
 
     def qsize(self):
@@ -112,7 +134,11 @@ 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.
+
+        Raises QueueShutDown if the queue has been shut down.
         """
+        if not self._is_alive():
+            raise QueueShutDown
         while self.full():
             putter = self._get_loop().create_future()
             self._putters.append(putter)
@@ -125,20 +151,26 @@ async def put(self, item):
                     self._putters.remove(putter)
                 except ValueError:
                     # The putter could be removed from self._putters by a
-                    # previous get_nowait call.
+                    # previous get_nowait call or a shutdown call.
                     pass
                 if not self.full() and not putter.cancelled():
                     # We were woken up by get_nowait(), but can't take
                     # the call.  Wake up the next in line.
                     self._wakeup_next(self._putters)
                 raise
+            if not self._is_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.
+
+        Raises QueueShutDown if the queue has been shut down.
         """
+        if not self._is_alive():
+            raise QueueShutDown
         if self.full():
             raise QueueFull
         self._put(item)
@@ -150,8 +182,15 @@ async def get(self):
         """Remove and return an item from the queue.
 
         If queue is empty, wait until an item is available.
+
+        Raises QueueShutDown if the queue has been shut down and is empty, or
+        if the queue has been shut down immediately.
         """
+        if self._is_shutdown_immediate():
+            raise QueueShutDown
         while self.empty():
+            if self._is_shutdown():
+                raise QueueShutDown
             getter = self._get_loop().create_future()
             self._getters.append(getter)
             try:
@@ -163,21 +202,31 @@ async def get(self):
                     self._getters.remove(getter)
                 except ValueError:
                     # The getter could be removed from self._getters by a
-                    # previous put_nowait call.
+                    # previous put_nowait call,
+                    # or a shutdown call.
                     pass
                 if not self.empty() and not getter.cancelled():
                     # We were woken up by put_nowait(), but can't take
                     # the call.  Wake up the next in line.
                     self._wakeup_next(self._getters)
                 raise
+            if self._is_shutdown_immediate():
+                raise QueueShutDown
         return self.get_nowait()
 
     def get_nowait(self):
         """Remove and return an item from the queue.
 
         Return an item if one is immediately available, else raise QueueEmpty.
+
+        Raises QueueShutDown if the queue has been shut down and is empty, or
+        if the queue has been shut down immediately.
         """
+        if self._is_shutdown_immediate():
+            raise QueueShutDown
         if self.empty():
+            if self._is_shutdown():
+                raise QueueShutDown
             raise QueueEmpty
         item = self._get()
         self._wakeup_next(self._putters)
@@ -196,7 +245,11 @@ def task_done(self):
 
         Raises ValueError if called more times than there were items placed in
         the queue.
+
+        Raises QueueShutDown if the queue has been shut down immediately.
         """
+        if self._is_shutdown_immediate():
+            raise QueueShutDown
         if self._unfinished_tasks <= 0:
             raise ValueError('task_done() called too many times')
         self._unfinished_tasks -= 1
@@ -210,9 +263,57 @@ async def join(self):
         queue. The count goes down whenever a consumer calls task_done() to
         indicate that the item was retrieved and all work on it is complete.
         When the count of unfinished tasks drops to zero, join() unblocks.
+
+        Raises QueueShutDown if the queue has been shut down immediately.
         """
+        if self._is_shutdown_immediate():
+            raise QueueShutDown
         if self._unfinished_tasks > 0:
             await self._finished.wait()
+            if self._is_shutdown_immediate():
+                raise QueueShutDown
+
+    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 self._is_shutdown_immediate():
+            return
+        # here _shutdown_state is ALIVE or SHUTDOWN
+        if immediate:
+            self._set_shutdown_immediate()
+            while self._getters:
+                getter = self._getters.popleft()
+                if not getter.done():
+                    getter.set_result(None)
+            # Release all 'blocked' tasks/coros in `join()`
+            self._finished.set()
+        else:
+            self._set_shutdown()
+        while self._putters:
+            putter = self._putters.popleft()
+            if not putter.done():
+                putter.set_result(None)
+
+    def _is_alive(self):
+        return self._shutdown_state is _QueueState.ALIVE
+
+    def _is_shutdown(self):
+        return self._shutdown_state is _QueueState.SHUTDOWN
+
+    def _is_shutdown_immediate(self):
+        return self._shutdown_state is _QueueState.SHUTDOWN_IMMEDIATE
+
+    def _set_shutdown(self):
+        self._shutdown_state = _QueueState.SHUTDOWN
+
+    def _set_shutdown_immediate(self):
+        self._shutdown_state = _QueueState.SHUTDOWN_IMMEDIATE
 
 
 class PriorityQueue(Queue):