aboutsummaryrefslogtreecommitdiffstats
path: root/contrib/tools/python3/src/Lib/multiprocessing/heap.py
blob: 6217dfe12689b379f2dad6f1e4bc3bbf6af8f60a (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
#
# 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
from collections import defaultdict
import mmap
import os
import sys
import tempfile
import threading

from .context import reduction, assert_spawning
from . import util

__all__ = ['BufferWrapper']

#
# Inheritable class which wraps an mmap, and from which blocks can be allocated
#

if sys.platform == 'win32':

    import _winapi

    class Arena(object):
        """
        A shared memory area backed by anonymous memory (Windows).
        """

        _rand = tempfile._RandomNameSequence()

        def __init__(self, size):
            self.size = size
            for i in range(100):
                name = 'pym-%d-%s' % (os.getpid(), next(self._rand))
                buf = mmap.mmap(-1, size, tagname=name)
                if _winapi.GetLastError() == 0:
                    break
                # We have reopened a preexisting mmap.
                buf.close()
            else:
                raise FileExistsError('Cannot find name for new mmap')
            self.name = name
            self.buffer = buf
            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
            # Reopen existing mmap
            self.buffer = mmap.mmap(-1, self.size, tagname=self.name)
            # XXX Temporarily preventing buildbot failures while determining
            # XXX the correct long-term fix. See issue 23060
            #assert _winapi.GetLastError() == _winapi.ERROR_ALREADY_EXISTS

else:

    class Arena(object):
        """
        A shared memory area backed by a temporary file (POSIX).
        """

        if sys.platform == 'linux':
            _dir_candidates = ['/dev/shm']
        else:
            _dir_candidates = []

        def __init__(self, size, fd=-1):
            self.size = size
            self.fd = fd
            if fd == -1:
                # Arena is created anew (if fd != -1, it means we're coming
                # from rebuild_arena() below)
                self.fd, name = tempfile.mkstemp(
                     prefix='pym-%d-'%os.getpid(),
                     dir=self._choose_dir(size))
                os.unlink(name)
                util.Finalize(self, os.close, (self.fd,))
                os.ftruncate(self.fd, size)
            self.buffer = mmap.mmap(self.fd, self.size)

        def _choose_dir(self, size):
            # Choose a non-storage backed directory if possible,
            # to improve performance
            for d in self._dir_candidates:
                st = os.statvfs(d)
                if st.f_bavail * st.f_frsize >= size:  # enough free space?
                    return d
            return util.get_temp_dir()

    def reduce_arena(a):
        if a.fd == -1:
            raise ValueError('Arena is unpicklable because '
                             'forking was enabled when it was created')
        return rebuild_arena, (a.size, reduction.DupFd(a.fd))

    def rebuild_arena(size, dupfd):
        return Arena(size, dupfd.detach())

    reduction.register(Arena, reduce_arena)

#
# Class allowing allocation of chunks of memory from arenas
#

class Heap(object):

    # Minimum malloc() alignment
    _alignment = 8

    _DISCARD_FREE_SPACE_LARGER_THAN = 4 * 1024 ** 2  # 4 MB
    _DOUBLE_ARENA_SIZE_UNTIL = 4 * 1024 ** 2

    def __init__(self, size=mmap.PAGESIZE):
        self._lastpid = os.getpid()
        self._lock = threading.Lock()
        # Current arena allocation size
        self._size = size
        # A sorted list of available block sizes in arenas
        self._lengths = []

        # Free block management:
        # - map each block size to a list of `(Arena, start, stop)` blocks
        self._len_to_seq = {}
        # - map `(Arena, start)` tuple to the `(Arena, start, stop)` block
        #   starting at that offset
        self._start_to_block = {}
        # - map `(Arena, stop)` tuple to the `(Arena, start, stop)` block
        #   ending at that offset
        self._stop_to_block = {}

        # Map arenas to their `(Arena, start, stop)` blocks in use
        self._allocated_blocks = defaultdict(set)
        self._arenas = []

        # List of pending blocks to free - see comment in free() below
        self._pending_free_blocks = []

        # Statistics
        self._n_mallocs = 0
        self._n_frees = 0

    @staticmethod
    def _roundup(n, alignment):
        # alignment must be a power of 2
        mask = alignment - 1
        return (n + mask) & ~mask

    def _new_arena(self, size):
        # Create a new arena with at least the given *size*
        length = self._roundup(max(self._size, size), mmap.PAGESIZE)
        # We carve larger and larger arenas, for efficiency, until we
        # reach a large-ish size (roughly L3 cache-sized)
        if self._size < self._DOUBLE_ARENA_SIZE_UNTIL:
            self._size *= 2
        util.info('allocating a new mmap of length %d', length)
        arena = Arena(length)
        self._arenas.append(arena)
        return (arena, 0, length)

    def _discard_arena(self, arena):
        # Possibly delete the given (unused) arena
        length = arena.size
        # Reusing an existing arena is faster than creating a new one, so
        # we only reclaim space if it's large enough.
        if length < self._DISCARD_FREE_SPACE_LARGER_THAN:
            return
        blocks = self._allocated_blocks.pop(arena)
        assert not blocks
        del self._start_to_block[(arena, 0)]
        del self._stop_to_block[(arena, length)]
        self._arenas.remove(arena)
        seq = self._len_to_seq[length]
        seq.remove((arena, 0, length))
        if not seq:
            del self._len_to_seq[length]
            self._lengths.remove(length)

    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):
            return self._new_arena(size)
        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 _add_free_block(self, block):
        # make block available and try to merge with its neighbours in the arena
        (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 _remove_allocated_block(self, block):
        arena, start, stop = block
        blocks = self._allocated_blocks[arena]
        blocks.remove((start, stop))
        if not blocks:
            # Arena is entirely free, discard it from this process
            self._discard_arena(arena)

    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._add_free_block(block)
            self._remove_allocated_block(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).
        if os.getpid() != self._lastpid:
            raise ValueError(
                "My pid ({0:n}) is not last pid {1:n}".format(
                    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._n_frees += 1
                self._free_pending_blocks()
                self._add_free_block(block)
                self._remove_allocated_block(block)
            finally:
                self._lock.release()

    def malloc(self, size):
        # return a block of right size (possibly rounded up)
        if size < 0:
            raise ValueError("Size {0:n} out of range".format(size))
        if sys.maxsize <= size:
            raise OverflowError("Size {0:n} too large".format(size))
        if os.getpid() != self._lastpid:
            self.__init__()                     # reinitialize after fork
        with self._lock:
            self._n_mallocs += 1
            # allow pending blocks to be marked available
            self._free_pending_blocks()
            size = self._roundup(max(size, 1), self._alignment)
            (arena, start, stop) = self._malloc(size)
            real_stop = start + size
            if real_stop < stop:
                # if the returned block is larger than necessary, mark
                # the remainder available
                self._add_free_block((arena, real_stop, stop))
            self._allocated_blocks[arena].add((start, real_stop))
            return (arena, start, real_stop)

#
# Class wrapping a block allocated out of a Heap -- can be inherited by child process
#

class BufferWrapper(object):

    _heap = Heap()

    def __init__(self, size):
        if size < 0:
            raise ValueError("Size {0:n} out of range".format(size))
        if sys.maxsize <= size:
            raise OverflowError("Size {0:n} too large".format(size))
        block = BufferWrapper._heap.malloc(size)
        self._state = (block, size)
        util.Finalize(self, BufferWrapper._heap.free, args=(block,))

    def create_memoryview(self):
        (arena, start, stop), size = self._state
        return memoryview(arena.buffer)[start:start+size]