Editing: heap.py
# # Module which supports allocation of memory from an mmap # # multiprocessing/heap.py # # 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. # import bisect import mmap import tempfile import os import sys import threading import itertools import _multiprocessing from multiprocessing.util import Finalize, info from multiprocessing.forking import assert_spawning __all__ = ['BufferWrapper'] # # Inheirtable class which wraps an mmap, and from which blocks can be allocated # if sys.platform == 'win32': from _multiprocessing import win32 class Arena(object): _counter = itertools.count() def __init__(self, size): self.size = size self.name = 'pym-%d-%d' % (os.getpid(), Arena._counter.next()) self.buffer = mmap.mmap(-1, self.size, tagname=self.name) assert win32.GetLastError() == 0, 'tagname already in use' self._state = (self.size, self.name) def __getstate__(self): assert_spawning(self) return self._state def __setstate__(self, state): self.size, self.name = self._state = state self.buffer = mmap.mmap(-1, self.size, tagname=self.name) assert win32.GetLastError() == win32.ERROR_ALREADY_EXISTS else: class Arena(object): def __init__(self, size): self.buffer = mmap.mmap(-1, size) self.size = size self.name = None # # Class allowing allocation of chunks of memory from arenas # class Heap(object): _alignment = 8 def __init__(self, size=mmap.PAGESIZE): self._lastpid = os.getpid() self._lock = threading.Lock() self._size = size self._lengths = [] self._len_to_seq = {} self._start_to_block = {} 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): # alignment must be a power of 2 mask = alignment - 1 return (n + mask) & ~mask def _malloc(self, size): # returns a large enough block -- it might be much larger i = bisect.bisect_left(self._lengths, size) if i == len(self._lengths): length = self._roundup(max(self._size, size), mmap.PAGESIZE) self._size *= 2 info('allocating a new mmap of length %d', length) arena = Arena(length) self._arenas.append(arena) return (arena, 0, length) else: length = self._lengths[i] seq = self._len_to_seq[length] block = seq.pop() if not seq: del self._len_to_seq[length], self._lengths[i] (arena, start, stop) = block del self._start_to_block[(arena, start)] del self._stop_to_block[(arena, stop)] return block def _free(self, block): # free location and try to merge with neighbours (arena, start, stop) = block try: prev_block = self._stop_to_block[(arena, start)] except KeyError: pass else: start, _ = self._absorb(prev_block) try: next_block = self._start_to_block[(arena, stop)] except KeyError: pass else: _, stop = self._absorb(next_block) block = (arena, start, stop) length = stop - start try: self._len_to_seq[length].append(block) except KeyError: self._len_to_seq[length] = [block] bisect.insort(self._lengths, length) self._start_to_block[(arena, start)] = block self._stop_to_block[(arena, stop)] = block def _absorb(self, block): # deregister this block so it can be merged with a neighbour (arena, start, stop) = block del self._start_to_block[(arena, start)] del self._stop_to_block[(arena, stop)] length = stop - start seq = self._len_to_seq[length] seq.remove(block) if not seq: del self._len_to_seq[length] self._lengths.remove(length) 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 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) assert 0 <= size < sys.maxint 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) new_stop = start + size if new_stop < stop: self._free((arena, new_stop, stop)) block = (arena, start, new_stop) self._allocated_blocks.add(block) return block finally: self._lock.release() # # Class representing a chunk of an mmap -- can be inherited # class BufferWrapper(object): _heap = Heap() def __init__(self, size): assert 0 <= size < sys.maxint block = BufferWrapper._heap.malloc(size) self._state = (block, size) Finalize(self, BufferWrapper._heap.free, args=(block,)) def get_address(self): (arena, start, stop), size = self._state address, length = _multiprocessing.address_of_buffer(arena.buffer) assert size <= length return address + start def get_size(self): return self._state[1]
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