[Python-checkins] cpython (3.2): Issue #14406: Fix a race condition when using

[antoine.pitrou]

http://hg.python.org/cpython/rev/0312db5265d0
changeset:   76025:0312db5265d0
branch:      3.2
parent:      76021:6774a2285579
user:        Antoine Pitrou <solipsis at pitrou.net>
date:        Sat Mar 31 20:23:30 2012 +0200
summary:
  Issue #14406: Fix a race condition when using `concurrent.futures.wait(return_when=ALL_COMPLETED)`.
Patch by Matt Joiner.

files:
  Lib/concurrent/futures/_base.py     |   8 ++++--
  Lib/test/test_concurrent_futures.py |  18 ++++++++++++++++-
  Misc/NEWS                           |   3 ++
  3 files changed, 25 insertions(+), 4 deletions(-)


diff --git a/Lib/concurrent/futures/_base.py b/Lib/concurrent/futures/_base.py
--- a/Lib/concurrent/futures/_base.py
+++ b/Lib/concurrent/futures/_base.py
@@ -112,12 +112,14 @@
     def __init__(self, num_pending_calls, stop_on_exception):
         self.num_pending_calls = num_pending_calls
         self.stop_on_exception = stop_on_exception
+        self.lock = threading.Lock()
         super().__init__()
 
     def _decrement_pending_calls(self):
-        self.num_pending_calls -= 1
-        if not self.num_pending_calls:
-            self.event.set()
+        with self.lock:
+            self.num_pending_calls -= 1
+            if not self.num_pending_calls:
+                self.event.set()
 
     def add_result(self, future):
         super().add_result(future)
diff --git a/Lib/test/test_concurrent_futures.py b/Lib/test/test_concurrent_futures.py
--- a/Lib/test/test_concurrent_futures.py
+++ b/Lib/test/test_concurrent_futures.py
@@ -183,7 +183,9 @@
         for p in processes:
             p.join()
 
+
 class WaitTests(unittest.TestCase):
+
     def test_first_completed(self):
         future1 = self.executor.submit(mul, 21, 2)
         future2 = self.executor.submit(time.sleep, 1.5)
@@ -284,7 +286,21 @@
 
 
 class ThreadPoolWaitTests(ThreadPoolMixin, WaitTests):
-    pass
+
+    def test_pending_calls_race(self):
+        # Issue #14406: multi-threaded race condition when waiting on all
+        # futures.
+        event = threading.Event()
+        def future_func():
+            event.wait()
+        oldswitchinterval = sys.getswitchinterval()
+        sys.setswitchinterval(1e-6)
+        try:
+            fs = {self.executor.submit(future_func) for i in range(100)}
+            event.set()
+            futures.wait(fs, return_when=futures.ALL_COMPLETED)
+        finally:
+            sys.setswitchinterval(oldswitchinterval)
 
 
 class ProcessPoolWaitTests(ProcessPoolMixin, WaitTests):
diff --git a/Misc/NEWS b/Misc/NEWS
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -31,6 +31,9 @@
 Library
 -------
 
+- Issue #14406: Fix a race condition when using ``concurrent.futures.wait(
+  return_when=ALL_COMPLETED)``.  Patch by Matt Joiner.
+
 - Issue #14409: IDLE now properly executes commands in the Shell window
   when it cannot read the normal config files on startup and
   has to use the built-in default key bindings.

-- 
Repository URL: http://hg.python.org/cpython