gh-96471: Add shutdown() method to queue.Queue (#104750)

Co-authored-by: Duprat <yduprat@gmail.com>

Lib/queue.py

@@ -25,6 +25,10 @@ class Full(Exception):
     pass
 
 
+class ShutDown(Exception):
+    '''Raised when put/get with shut-down queue.'''
+
+
 class Queue:
     '''Create a queue object with a given maximum size.
 
@@ -54,6 +58,9 @@ def __init__(self, maxsize=0):
         self.all_tasks_done = threading.Condition(self.mutex)
         self.unfinished_tasks = 0
 
+        # Queue shutdown state
+        self.is_shutdown = False
+
     def task_done(self):
         '''Indicate that a formerly enqueued task is complete.
 
@@ -67,6 +74,8 @@ def task_done(self):
 
         Raises a ValueError if called more times than there were items
         placed in the queue.
+
+        Raises ShutDown if the queue has been shut down immediately.
         '''
         with self.all_tasks_done:
             unfinished = self.unfinished_tasks - 1
@@ -84,6 +93,8 @@ def join(self):
         to indicate the item was retrieved and all work on it is complete.
 
         When the count of unfinished tasks drops to zero, join() unblocks.
+
+        Raises ShutDown if the queue has been shut down immediately.
         '''
         with self.all_tasks_done:
             while self.unfinished_tasks:
@@ -129,8 +140,12 @@ def put(self, item, block=True, timeout=None):
         Otherwise ('block' is false), put an item on the queue if a free slot
         is immediately available, else raise the Full exception ('timeout'
         is ignored in that case).
+
+        Raises ShutDown if the queue has been shut down.
         '''
         with self.not_full:
+            if self.is_shutdown:
+                raise ShutDown
             if self.maxsize > 0:
                 if not block:
                     if self._qsize() >= self.maxsize:
@@ -138,6 +153,8 @@ def put(self, item, block=True, timeout=None):
                 elif timeout is None:
                     while self._qsize() >= self.maxsize:
                         self.not_full.wait()
+                        if self.is_shutdown:
+                            raise ShutDown
                 elif timeout < 0:
                     raise ValueError("'timeout' must be a non-negative number")
                 else:
@@ -147,6 +164,8 @@ def put(self, item, block=True, timeout=None):
                         if remaining <= 0.0:
                             raise Full
                         self.not_full.wait(remaining)
+                        if self.is_shutdown:
+                            raise ShutDown
             self._put(item)
             self.unfinished_tasks += 1
             self.not_empty.notify()
@@ -161,14 +180,21 @@ def get(self, block=True, timeout=None):
         Otherwise ('block' is false), return an item if one is immediately
         available, else raise the Empty exception ('timeout' is ignored
         in that case).
+
+        Raises ShutDown if the queue has been shut down and is empty,
+        or if the queue has been shut down immediately.
         '''
         with self.not_empty:
+            if self.is_shutdown and not self._qsize():
+                raise ShutDown
             if not block:
                 if not self._qsize():
                     raise Empty
             elif timeout is None:
                 while not self._qsize():
                     self.not_empty.wait()
+                    if self.is_shutdown and not self._qsize():
+                        raise ShutDown
             elif timeout < 0:
                 raise ValueError("'timeout' must be a non-negative number")
             else:
@@ -178,6 +204,8 @@ def get(self, block=True, timeout=None):
                     if remaining <= 0.0:
                         raise Empty
                     self.not_empty.wait(remaining)
+                    if self.is_shutdown and not self._qsize():
+                        raise ShutDown
             item = self._get()
             self.not_full.notify()
             return item
@@ -198,6 +226,28 @@ def get_nowait(self):
         '''
         return self.get(block=False)
 
+    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 ShutDown exception is raised.
+        '''
+        with self.mutex:
+            self.is_shutdown = True
+            if immediate:
+                n_items = self._qsize()
+                while self._qsize():
+                    self._get()
+                    if self.unfinished_tasks > 0:
+                        self.unfinished_tasks -= 1
+                self.not_empty.notify_all()
+                # release all blocked threads in `join()`
+                self.all_tasks_done.notify_all()
+            self.not_full.notify_all()
+
     # Override these methods to implement other queue organizations
     # (e.g. stack or priority queue).
     # These will only be called with appropriate locks held