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1#
2# Module which supports allocation of memory from an mmap
3#
4# multiprocessing/heap.py
5#
6# Copyright (c) 2006-2008, R Oudkerk
7# All rights reserved.
8#
9# Redistribution and use in source and binary forms, with or without
10# modification, are permitted provided that the following conditions
11# are met:
12#
13# 1. Redistributions of source code must retain the above copyright
14#    notice, this list of conditions and the following disclaimer.
15# 2. Redistributions in binary form must reproduce the above copyright
16#    notice, this list of conditions and the following disclaimer in the
17#    documentation and/or other materials provided with the distribution.
18# 3. Neither the name of author nor the names of any contributors may be
19#    used to endorse or promote products derived from this software
20#    without specific prior written permission.
21#
22# THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS "AS IS" AND
23# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25# ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
26# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28# OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29# HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31# OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32# SUCH DAMAGE.
33#
34
35import bisect
36import mmap
37import tempfile
38import os
39import sys
40import threading
41import itertools
42
43import _multiprocessing
44from multiprocessing.util import Finalize, info
45from multiprocessing.forking import assert_spawning
46
47__all__ = ['BufferWrapper']
48
49#
50# Inheirtable class which wraps an mmap, and from which blocks can be allocated
51#
52
53if sys.platform == 'win32':
54
55    from _multiprocessing import win32
56
57    class Arena(object):
58
59        _counter = itertools.count()
60
61        def __init__(self, size):
62            self.size = size
63            self.name = 'pym-%d-%d' % (os.getpid(), Arena._counter.next())
64            self.buffer = mmap.mmap(-1, self.size, tagname=self.name)
65            assert win32.GetLastError() == 0, 'tagname already in use'
66            self._state = (self.size, self.name)
67
68        def __getstate__(self):
69            assert_spawning(self)
70            return self._state
71
72        def __setstate__(self, state):
73            self.size, self.name = self._state = state
74            self.buffer = mmap.mmap(-1, self.size, tagname=self.name)
75            assert win32.GetLastError() == win32.ERROR_ALREADY_EXISTS
76
77else:
78
79    class Arena(object):
80
81        def __init__(self, size):
82            self.buffer = mmap.mmap(-1, size)
83            self.size = size
84            self.name = None
85
86#
87# Class allowing allocation of chunks of memory from arenas
88#
89
90class Heap(object):
91
92    _alignment = 8
93
94    def __init__(self, size=mmap.PAGESIZE):
95        self._lastpid = os.getpid()
96        self._lock = threading.Lock()
97        self._size = size
98        self._lengths = []
99        self._len_to_seq = {}
100        self._start_to_block = {}
101        self._stop_to_block = {}
102        self._allocated_blocks = set()
103        self._arenas = []
104        # list of pending blocks to free - see free() comment below
105        self._pending_free_blocks = []
106
107    @staticmethod
108    def _roundup(n, alignment):
109        # alignment must be a power of 2
110        mask = alignment - 1
111        return (n + mask) & ~mask
112
113    def _malloc(self, size):
114        # returns a large enough block -- it might be much larger
115        i = bisect.bisect_left(self._lengths, size)
116        if i == len(self._lengths):
117            length = self._roundup(max(self._size, size), mmap.PAGESIZE)
118            self._size *= 2
119            info('allocating a new mmap of length %d', length)
120            arena = Arena(length)
121            self._arenas.append(arena)
122            return (arena, 0, length)
123        else:
124            length = self._lengths[i]
125            seq = self._len_to_seq[length]
126            block = seq.pop()
127            if not seq:
128                del self._len_to_seq[length], self._lengths[i]
129
130        (arena, start, stop) = block
131        del self._start_to_block[(arena, start)]
132        del self._stop_to_block[(arena, stop)]
133        return block
134
135    def _free(self, block):
136        # free location and try to merge with neighbours
137        (arena, start, stop) = block
138
139        try:
140            prev_block = self._stop_to_block[(arena, start)]
141        except KeyError:
142            pass
143        else:
144            start, _ = self._absorb(prev_block)
145
146        try:
147            next_block = self._start_to_block[(arena, stop)]
148        except KeyError:
149            pass
150        else:
151            _, stop = self._absorb(next_block)
152
153        block = (arena, start, stop)
154        length = stop - start
155
156        try:
157            self._len_to_seq[length].append(block)
158        except KeyError:
159            self._len_to_seq[length] = [block]
160            bisect.insort(self._lengths, length)
161
162        self._start_to_block[(arena, start)] = block
163        self._stop_to_block[(arena, stop)] = block
164
165    def _absorb(self, block):
166        # deregister this block so it can be merged with a neighbour
167        (arena, start, stop) = block
168        del self._start_to_block[(arena, start)]
169        del self._stop_to_block[(arena, stop)]
170
171        length = stop - start
172        seq = self._len_to_seq[length]
173        seq.remove(block)
174        if not seq:
175            del self._len_to_seq[length]
176            self._lengths.remove(length)
177
178        return start, stop
179
180    def _free_pending_blocks(self):
181        # Free all the blocks in the pending list - called with the lock held.
182        while True:
183            try:
184                block = self._pending_free_blocks.pop()
185            except IndexError:
186                break
187            self._allocated_blocks.remove(block)
188            self._free(block)
189
190    def free(self, block):
191        # free a block returned by malloc()
192        # Since free() can be called asynchronously by the GC, it could happen
193        # that it's called while self._lock is held: in that case,
194        # self._lock.acquire() would deadlock (issue #12352). To avoid that, a
195        # trylock is used instead, and if the lock can't be acquired
196        # immediately, the block is added to a list of blocks to be freed
197        # synchronously sometimes later from malloc() or free(), by calling
198        # _free_pending_blocks() (appending and retrieving from a list is not
199        # strictly thread-safe but under cPython it's atomic thanks to the GIL).
200        assert os.getpid() == self._lastpid
201        if not self._lock.acquire(False):
202            # can't acquire the lock right now, add the block to the list of
203            # pending blocks to free
204            self._pending_free_blocks.append(block)
205        else:
206            # we hold the lock
207            try:
208                self._free_pending_blocks()
209                self._allocated_blocks.remove(block)
210                self._free(block)
211            finally:
212                self._lock.release()
213
214    def malloc(self, size):
215        # return a block of right size (possibly rounded up)
216        assert 0 <= size < sys.maxint
217        if os.getpid() != self._lastpid:
218            self.__init__()                     # reinitialize after fork
219        self._lock.acquire()
220        self._free_pending_blocks()
221        try:
222            size = self._roundup(max(size,1), self._alignment)
223            (arena, start, stop) = self._malloc(size)
224            new_stop = start + size
225            if new_stop < stop:
226                self._free((arena, new_stop, stop))
227            block = (arena, start, new_stop)
228            self._allocated_blocks.add(block)
229            return block
230        finally:
231            self._lock.release()
232
233#
234# Class representing a chunk of an mmap -- can be inherited
235#
236
237class BufferWrapper(object):
238
239    _heap = Heap()
240
241    def __init__(self, size):
242        assert 0 <= size < sys.maxint
243        block = BufferWrapper._heap.malloc(size)
244        self._state = (block, size)
245        Finalize(self, BufferWrapper._heap.free, args=(block,))
246
247    def get_address(self):
248        (arena, start, stop), size = self._state
249        address, length = _multiprocessing.address_of_buffer(arena.buffer)
250        assert size <= length
251        return address + start
252
253    def get_size(self):
254        return self._state[1]
255