#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.
diff --git a/Lib/test/test_threading_local.py b/Lib/test/test_threading_local.py
index b7dd538..8642141 100644
--- a/Lib/test/test_threading_local.py
+++ b/Lib/test/test_threading_local.py
@@ -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'))
diff --git a/Misc/NEWS b/Misc/NEWS
index f7c73b1..1dd586f 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -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,
diff --git a/Modules/threadmodule.c b/Modules/threadmodule.c
index 81bf288..a87ddb3 100644
--- a/Modules/threadmodule.c
+++ b/Modules/threadmodule.c
@@ -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;