From 8a250aeb2127683edb2bb10fdc529b94cd06afe3 Mon Sep 17 00:00:00 2001 From: Benjamin Peterson Date: Mon, 30 Jun 2008 23:30:24 +0000 Subject: Merged revisions 64601 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r64601 | amaury.forgeotdarc | 2008-06-30 17:42:40 -0500 (Mon, 30 Jun 2008) | 11 lines #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. ........ --- Lib/test/test_threading_local.py | 26 ++++++++++++++++++++++++++ Modules/_threadmodule.c | 5 ++++- 2 files changed, 30 insertions(+), 1 deletion(-) diff --git a/Lib/test/test_threading_local.py b/Lib/test/test_threading_local.py index e48dc59..977a38a 100644 --- a/Lib/test/test_threading_local.py +++ b/Lib/test/test_threading_local.py @@ -42,6 +42,32 @@ class ThreadingLocalTest(unittest.TestCase): 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')) diff --git a/Modules/_threadmodule.c b/Modules/_threadmodule.c index 0fe9a76..d2299aa 100644 --- a/Modules/_threadmodule.c +++ b/Modules/_threadmodule.c @@ -293,7 +293,10 @@ _ldict(localobject *self) } } - 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; -- cgit v0.12