Issue #12352: Fix a deadlock in multiprocessing.Heap when a block is freed by
the garbage collector while the Heap lock is held.
diff --git a/Lib/test/test_multiprocessing.py b/Lib/test/test_multiprocessing.py
index de5e46a..18a2f29 100644
--- a/Lib/test/test_multiprocessing.py
+++ b/Lib/test/test_multiprocessing.py
@@ -1615,6 +1615,8 @@
# verify the state of the heap
all = []
occupied = 0
+ heap._lock.acquire()
+ self.addCleanup(heap._lock.release)
for L in heap._len_to_seq.values():
for arena, start, stop in L:
all.append((heap._arenas.index(arena), start, stop,
@@ -1632,6 +1634,29 @@
self.assertTrue((arena != narena and nstart == 0) or
(stop == nstart))
+ def test_free_from_gc(self):
+ # Check that freeing of blocks by the garbage collector doesn't deadlock
+ # (issue #12352).
+ # Make sure the GC is enabled, and set lower collection thresholds to
+ # make collections more frequent (and increase the probability of
+ # deadlock).
+ if gc.isenabled():
+ thresholds = gc.get_threshold()
+ self.addCleanup(gc.set_threshold, *thresholds)
+ else:
+ gc.enable()
+ self.addCleanup(gc.disable)
+ gc.set_threshold(10)
+
+ # perform numerous block allocations, with cyclic references to make
+ # sure objects are collected asynchronously by the gc
+ for i in range(5000):
+ a = multiprocessing.heap.BufferWrapper(1)
+ b = multiprocessing.heap.BufferWrapper(1)
+ # circular references
+ a.buddy = b
+ b.buddy = a
+
#
#
#