Issue #22853: Fixed a deadlock when use multiprocessing.Queue at import time.

Patch by Florian Finkernagel and Davin Potts.

diff --git a/Lib/multiprocessing/queues.py b/Lib/multiprocessing/queues.py
index 433c7e29deeea14f99c0f302eefd1677cb2d0962..487e0afb6a76a35ddea79bc9f662337e2914ba16 100644 (file)
--- a/Lib/multiprocessing/queues.py
+++ b/Lib/multiprocessing/queues.py
@@ -44,10 +44,10 @@ import weakref
 
 from Queue import Empty, Full
 import _multiprocessing
-from multiprocessing import Pipe
-from multiprocessing.synchronize import Lock, BoundedSemaphore, Semaphore, Condition
-from multiprocessing.util import debug, info, Finalize, register_after_fork
-from multiprocessing.forking import assert_spawning
+from . import Pipe
+from .synchronize import Lock, BoundedSemaphore, Semaphore, Condition
+from .util import debug, info, Finalize, register_after_fork, is_exiting
+from .forking import assert_spawning
 
 #
 # Queue type using a pipe, buffer and thread
@@ -229,8 +229,6 @@ class Queue(object):
     @staticmethod
     def _feed(buffer, notempty, send, writelock, close):
         debug('starting thread to feed data to pipe')
-        from .util import is_exiting
-
         nacquire = notempty.acquire
         nrelease = notempty.release
         nwait = notempty.wait

diff --git a/Lib/test/test_multiprocessing.py b/Lib/test/test_multiprocessing.py
index ec4507ef74ef900edccea5b6f0f2e50282695ed3..b1e75b566325b07cac458ccd2983a45d5f890c43 100644 (file)
--- a/Lib/test/test_multiprocessing.py
+++ b/Lib/test/test_multiprocessing.py
@@ -620,6 +620,26 @@ class _TestQueue(BaseTestCase):
         for p in workers:
             p.join()
 
+    def test_no_import_lock_contention(self):
+        with test_support.temp_cwd():
+            module_name = 'imported_by_an_imported_module'
+            with open(module_name + '.py', 'w') as f:
+                f.write("""if 1:
+                    import multiprocessing
+
+                    q = multiprocessing.Queue()
+                    q.put('knock knock')
+                    q.get(timeout=3)
+                    q.close()
+                """)
+
+            with test_support.DirsOnSysPath(os.getcwd()):
+                try:
+                    __import__(module_name)
+                except Queue.Empty:
+                    self.fail("Probable regression on import lock contention;"
+                              " see Issue #22853")
+
 #
 #
 #

diff --git a/Misc/ACKS b/Misc/ACKS
index f03f34ea05138e883e59dd0e29df003e9f551428..e91e2a4f558ca304fa2fb53c7aa6bb2e82f471f1 100644 (file)
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -411,6 +411,7 @@ Vincent Fiack
 Anastasia Filatova
 Tomer Filiba
 Jeffrey Finkelstein
+Florian Finkernagel
 Russell Finn
 Dan Finnie
 Nils Fischbeck
@@ -1073,6 +1074,7 @@ Martin Pool
 Iustin Pop
 Claudiu Popa
 John Popplewell
+Davin Potts
 Guillaume Pratte
 Amrit Prem
 Paul Prescod

diff --git a/Misc/NEWS b/Misc/NEWS
index e24d40c24e7273a5a5a1716df5ccb8c0f2b73b97..a1ff5aa3548a8ee16c2b56c7803738ffaa3e99fd 100644 (file)
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -18,6 +18,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #22853: Fixed a deadlock when use multiprocessing.Queue at import time.
+  Patch by Florian Finkernagel and Davin Potts.
+
 - Issue #23476: In the ssl module, enable OpenSSL's X509_V_FLAG_TRUSTED_FIRST
   flag on certificate stores when it is available.