[Python-checkins] r64641 - in python/branches/release25-maint: Lib/test/test_threading_local.py Misc/NEWS Modules/threadmodule.c

Tue Jul 1 22:59:50 CEST 2008

Author: amaury.forgeotdarc
Date: Tue Jul 1 22:59:49 2008
New Revision: 64641
Log:
#Issue3088 in-progress: Race condition with instances of classes derived from threading.local:
When a thread touches such an object for the first time, a new thread-local __dict__ is created,
and the __init__ method is run.
But a thread switch can occur here; if the other thread touches the same object, it installs another
__dict__; when the first thread resumes, it updates the dictionary of the second...
This is the deep cause of the failures in test_multiprocessing involving "managers" objects.
Backport of r64601.
Modified:
 python/branches/release25-maint/Lib/test/test_threading_local.py
 python/branches/release25-maint/Misc/NEWS
 python/branches/release25-maint/Modules/threadmodule.c
Modified: python/branches/release25-maint/Lib/test/test_threading_local.py
==============================================================================

--- python/branches/release25-maint/Lib/test/test_threading_local.py	(original)
+++ python/branches/release25-maint/Lib/test/test_threading_local.py	Tue Jul 1 22:59:49 2008
@@ -2,6 +2,34 @@
 from doctest import DocTestSuite
 from test import test_support
 
+class ThreadingLocalTest(unittest.TestCase):
+ def test_derived(self):
+ # Issue 3088: if there is a threads switch inside the __init__
+ # of a threading.local derived class, the per-thread dictionary
+ # is created but not correctly set on the object.
+ # The first member set may be bogus.
+ import threading
+ import time
+ class Local(threading.local):
+ def __init__(self):
+ time.sleep(0.01)
+ local = Local()
+
+ def f(i):
+ local.x = i
+ # Simply check that the variable is correctly set
+ self.assertEqual(local.x, i)
+
+ threads= []
+ for i in range(10):
+ t = threading.Thread(target=f, args=(i,))
+ t.start()
+ threads.append(t)
+
+ for t in threads:
+ t.join()
+
+
 def test_main():
 suite = DocTestSuite('_threading_local')
 
@@ -19,6 +47,7 @@
 suite.addTest(DocTestSuite('_threading_local',
 setUp=setUp, tearDown=tearDown)
 )
+ suite.addTest(unittest.makeSuite(ThreadingLocalTest))
 
 test_support.run_suite(suite)
 
Modified: python/branches/release25-maint/Misc/NEWS
==============================================================================
--- python/branches/release25-maint/Misc/NEWS	(original)
+++ python/branches/release25-maint/Misc/NEWS	Tue Jul 1 22:59:49 2008
@@ -16,6 +16,10 @@
 set to a custom object whose write() method happens to install
 another file in sys.stdout.
 
+- Issue #3088: Corrected a race condition in classes derived from
+ threading.local: the first member set by a thread could be saved in
+ another thread's dictionary.
+
 - Issue #3100: Corrected a crash on deallocation of a subclassed weakref which
 holds the last (strong) reference to its referent.
 
Modified: python/branches/release25-maint/Modules/threadmodule.c
==============================================================================
--- python/branches/release25-maint/Modules/threadmodule.c	(original)
+++ python/branches/release25-maint/Modules/threadmodule.c	Tue Jul 1 22:59:49 2008
@@ -294,7 +294,10 @@
 		}
 		
 	}
-	else if (self->dict != ldict) {
+
+	/* The call to tp_init above may have caused another thread to run.
+	 Install our ldict again. */
+	if (self->dict != ldict) {
 		Py_CLEAR(self->dict);
 		Py_INCREF(ldict);
 		self->dict = ldict;
