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#
# Module which supports allocation of memory from an mmap
#
# multiprocessing/heap.py
#
# Copyright (c) 2006-2008, R Oudkerk
# Licensed to PSF under a Contributor Agreement.
#
import bisect
import mmap
import os
import sys
import threading
import itertools
import _multiprocessing
from multiprocessing.util import Finalize, info
from multiprocessing.forking import assert_spawning
__all__ = ['BufferWrapper']
#
# Inheritable class which wraps an mmap, and from which blocks can be allocated
#
if sys.platform == 'win32':
import _winapi
class Arena(object):
_counter = itertools.count()
def __init__(self, size):
self.size = size
self.name = 'pym-%d-%d' % (os.getpid(), next(Arena._counter))
self.buffer = mmap.mmap(-1, self.size, tagname=self.name)
assert _winapi.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 _winapi.GetLastError() == _winapi.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.maxsize
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 by child process
#
class BufferWrapper(object):
_heap = Heap()
def __init__(self, size):
assert 0 <= size < sys.maxsize
block = BufferWrapper._heap.malloc(size)
self._state = (block, size)
Finalize(self, BufferWrapper._heap.free, args=(block,))
def create_memoryview(self):
(arena, start, stop), size = self._state
return memoryview(arena.buffer)[start:start+size]