bpo-33078 - Fix queue size on pickling error (GH-6119)

1 files changed, 8 insertions, 2 deletions

diff --git a/Lib/multiprocessing/queues.py b/Lib/multiprocessing/queues.py
index d66d37a5c3..715a9b0e12 100644
--- a/Lib/multiprocessing/queues.py
+++ b/Lib/multiprocessing/queues.py
@@ -161,7 +161,7 @@ class Queue(object):
             target=Queue._feed,
             args=(self._buffer, self._notempty, self._send_bytes,
                   self._wlock, self._writer.close, self._ignore_epipe,
-                  self._on_queue_feeder_error),
+                  self._on_queue_feeder_error, self._sem),
             name='QueueFeederThread'
         )
         self._thread.daemon = True
@@ -203,7 +203,7 @@ class Queue(object):
 
     @staticmethod
     def _feed(buffer, notempty, send_bytes, writelock, close, ignore_epipe,
-              onerror):
+              onerror, queue_sem):
         debug('starting thread to feed data to pipe')
         nacquire = notempty.acquire
         nrelease = notempty.release
@@ -255,6 +255,12 @@ class Queue(object):
                     info('error in queue thread: %s', e)
                     return
                 else:
+                    # Since the object has not been sent in the queue, we need
+                    # to decrease the size of the queue. The error acts as
+                    # if the object had been silently removed from the queue
+                    # and this step is necessary to have a properly working
+                    # queue.
+                    queue_sem.release()
                     onerror(e, obj)
 
     @staticmethod