[Python-checkins] r64601 - in python/trunk: Lib/test/test_threading_local.py Misc/NEWS Modules/threadmodule.c

Tue Jul 1 00:42:40 CEST 2008

Author: amaury.forgeotdarc
Date: Tue Jul 1 00:42:40 2008
New Revision: 64601
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.
Also a 2.5 backport candidate.
Modified:
 python/trunk/Lib/test/test_threading_local.py
 python/trunk/Misc/NEWS
 python/trunk/Modules/threadmodule.c
Modified: python/trunk/Lib/test/test_threading_local.py
==============================================================================

--- python/trunk/Lib/test/test_threading_local.py	(original)
+++ python/trunk/Lib/test/test_threading_local.py	Tue Jul 1 00:42:40 2008
@@ -42,6 +42,32 @@
 deadlist = [weak for weak in weaklist if weak() is None]
 self.assert_(len(deadlist) in (n-1, n), (n, len(deadlist)))
 
+ 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 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 = unittest.TestSuite()
 suite.addTest(DocTestSuite('_threading_local'))
Modified: python/trunk/Misc/NEWS
==============================================================================
--- python/trunk/Misc/NEWS	(original)
+++ python/trunk/Misc/NEWS	Tue Jul 1 00:42:40 2008
@@ -10,6 +10,10 @@
 Core and Builtins
 -----------------
 
+- 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 #3004: Minor change to slice.indices(): the start and stop
 arguments are now treated identically, making the behaviour easier
 to describe and understand. For example, slice(None, -10,
Modified: python/trunk/Modules/threadmodule.c
==============================================================================
--- python/trunk/Modules/threadmodule.c	(original)
+++ python/trunk/Modules/threadmodule.c	Tue Jul 1 00:42:40 2008
@@ -293,7 +293,10 @@
 		}
 		
 	}
-	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;
