Changeset 391 for python/trunk/Lib/multiprocessing/heap.py

Timestamp:

Mar 19, 2014, 11:31:01 PM (11 years ago)

Author:

dmik

Message:

python: Merge vendor 2.7.6 to trunk.

Location:

python/trunk

Files:

• . (modified) (1 prop)
• Lib/multiprocessing/heap.py (modified) (5 diffs)

python/trunk/Lib/multiprocessing/heap.py

@@ -4 +4 @@
 # multiprocessing/heap.py
 #
-# Copyright (c) 2007-2008, R Oudkerk --- see COPYING.txt
+# Copyright (c) 2006-2008, R Oudkerk
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+#
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in the
+#    documentation and/or other materials provided with the distribution.
+# 3. Neither the name of author nor the names of any contributors may be
+#    used to endorse or promote products derived from this software
+#    without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS "AS IS" AND
+# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+# ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+# OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+# HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+# OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+# SUCH DAMAGE.
 #
 
@@ -27 +53 @@
 if sys.platform == 'win32':
 
-    from ._multiprocessing import win32
+    from _multiprocessing import win32
 
     class Arena(object):
@@ -76 +102 @@
         self._allocated_blocks = set()
         self._arenas = []
+        # list of pending blocks to free - see free() comment below
+        self._pending_free_blocks = []
 
     @staticmethod
@@ -150 +178 @@
         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):
@@ -166 +218 @@
             self.__init__()                     # reinitialize after fork
         self._lock.acquire()
+        self._free_pending_blocks()
         try:
             size = self._roundup(max(size,1), self._alignment)