diff options
author | Charles-François Natali <neologix@free.fr> | 2011-07-02 11:56:19 (GMT) |
---|---|---|
committer | Charles-François Natali <neologix@free.fr> | 2011-07-02 11:56:19 (GMT) |
commit | 414d0faedced1b7cb3585e76e0bdfff1795e15f3 (patch) | |
tree | 8ed8c8cc1debe19c9542cd063b514e9b4f3e6d17 /Lib/multiprocessing | |
parent | ff48c0a89b501df92c78873352956348d5cb0690 (diff) | |
download | cpython-414d0faedced1b7cb3585e76e0bdfff1795e15f3.zip cpython-414d0faedced1b7cb3585e76e0bdfff1795e15f3.tar.gz cpython-414d0faedced1b7cb3585e76e0bdfff1795e15f3.tar.bz2 |
Issue #12352: Fix a deadlock in multiprocessing.Heap when a block is freed by
the garbage collector while the Heap lock is held.
Diffstat (limited to 'Lib/multiprocessing')
-rw-r--r-- | Lib/multiprocessing/heap.py | 39 |
1 files changed, 33 insertions, 6 deletions
diff --git a/Lib/multiprocessing/heap.py b/Lib/multiprocessing/heap.py index 52ee49d..a1f3711 100644 --- a/Lib/multiprocessing/heap.py +++ b/Lib/multiprocessing/heap.py @@ -101,6 +101,8 @@ class Heap(object): self._stop_to_block = {} self._allocated_blocks = set() self._arenas = [] + # list of pending blocks to free - see free() comment below + self._pending_free_blocks = [] @staticmethod def _roundup(n, alignment): @@ -175,15 +177,39 @@ class Heap(object): return start, stop + def _free_pending_blocks(self): + # Free all the blocks in the pending list - called with the lock held. + while True: + try: + block = self._pending_free_blocks.pop() + except IndexError: + break + self._allocated_blocks.remove(block) + self._free(block) + def free(self, block): # free a block returned by malloc() + # Since free() can be called asynchronously by the GC, it could happen + # that it's called while self._lock is held: in that case, + # self._lock.acquire() would deadlock (issue #12352). To avoid that, a + # trylock is used instead, and if the lock can't be acquired + # immediately, the block is added to a list of blocks to be freed + # synchronously sometimes later from malloc() or free(), by calling + # _free_pending_blocks() (appending and retrieving from a list is not + # strictly thread-safe but under cPython it's atomic thanks to the GIL). assert os.getpid() == self._lastpid - self._lock.acquire() - try: - self._allocated_blocks.remove(block) - self._free(block) - finally: - self._lock.release() + if not self._lock.acquire(False): + # can't acquire the lock right now, add the block to the list of + # pending blocks to free + self._pending_free_blocks.append(block) + else: + # we hold the lock + try: + self._free_pending_blocks() + self._allocated_blocks.remove(block) + self._free(block) + finally: + self._lock.release() def malloc(self, size): # return a block of right size (possibly rounded up) @@ -191,6 +217,7 @@ class Heap(object): if os.getpid() != self._lastpid: self.__init__() # reinitialize after fork self._lock.acquire() + self._free_pending_blocks() try: size = self._roundup(max(size,1), self._alignment) (arena, start, stop) = self._malloc(size) |