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e4679cd644
Large shared arrays allocated using multiprocessing would remain allocated until the process ends.
337 lines
11 KiB
Python
337 lines
11 KiB
Python
#
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# Module which supports allocation of memory from an mmap
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#
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# multiprocessing/heap.py
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#
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# Copyright (c) 2006-2008, R Oudkerk
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# Licensed to PSF under a Contributor Agreement.
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#
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import bisect
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from collections import defaultdict
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import mmap
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import os
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import sys
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import tempfile
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import threading
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from .context import reduction, assert_spawning
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from . import util
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__all__ = ['BufferWrapper']
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#
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# Inheritable class which wraps an mmap, and from which blocks can be allocated
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#
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if sys.platform == 'win32':
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import _winapi
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class Arena(object):
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"""
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A shared memory area backed by anonymous memory (Windows).
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"""
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_rand = tempfile._RandomNameSequence()
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def __init__(self, size):
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self.size = size
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for i in range(100):
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name = 'pym-%d-%s' % (os.getpid(), next(self._rand))
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buf = mmap.mmap(-1, size, tagname=name)
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if _winapi.GetLastError() == 0:
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break
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# We have reopened a preexisting mmap.
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buf.close()
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else:
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raise FileExistsError('Cannot find name for new mmap')
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self.name = name
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self.buffer = buf
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self._state = (self.size, self.name)
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def __getstate__(self):
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assert_spawning(self)
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return self._state
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def __setstate__(self, state):
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self.size, self.name = self._state = state
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# Reopen existing mmap
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self.buffer = mmap.mmap(-1, self.size, tagname=self.name)
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# XXX Temporarily preventing buildbot failures while determining
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# XXX the correct long-term fix. See issue 23060
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#assert _winapi.GetLastError() == _winapi.ERROR_ALREADY_EXISTS
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else:
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class Arena(object):
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"""
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A shared memory area backed by a temporary file (POSIX).
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"""
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if sys.platform == 'linux':
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_dir_candidates = ['/dev/shm']
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else:
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_dir_candidates = []
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def __init__(self, size, fd=-1):
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self.size = size
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self.fd = fd
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if fd == -1:
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# Arena is created anew (if fd != -1, it means we're coming
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# from rebuild_arena() below)
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self.fd, name = tempfile.mkstemp(
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prefix='pym-%d-'%os.getpid(),
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dir=self._choose_dir(size))
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os.unlink(name)
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util.Finalize(self, os.close, (self.fd,))
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os.ftruncate(self.fd, size)
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self.buffer = mmap.mmap(self.fd, self.size)
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def _choose_dir(self, size):
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# Choose a non-storage backed directory if possible,
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# to improve performance
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for d in self._dir_candidates:
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st = os.statvfs(d)
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if st.f_bavail * st.f_frsize >= size: # enough free space?
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return d
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return util.get_temp_dir()
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def reduce_arena(a):
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if a.fd == -1:
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raise ValueError('Arena is unpicklable because '
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'forking was enabled when it was created')
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return rebuild_arena, (a.size, reduction.DupFd(a.fd))
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def rebuild_arena(size, dupfd):
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return Arena(size, dupfd.detach())
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reduction.register(Arena, reduce_arena)
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#
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# Class allowing allocation of chunks of memory from arenas
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#
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class Heap(object):
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# Minimum malloc() alignment
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_alignment = 8
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_DISCARD_FREE_SPACE_LARGER_THAN = 4 * 1024 ** 2 # 4 MB
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_DOUBLE_ARENA_SIZE_UNTIL = 4 * 1024 ** 2
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def __init__(self, size=mmap.PAGESIZE):
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self._lastpid = os.getpid()
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self._lock = threading.Lock()
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# Current arena allocation size
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self._size = size
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# A sorted list of available block sizes in arenas
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self._lengths = []
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# Free block management:
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# - map each block size to a list of `(Arena, start, stop)` blocks
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self._len_to_seq = {}
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# - map `(Arena, start)` tuple to the `(Arena, start, stop)` block
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# starting at that offset
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self._start_to_block = {}
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# - map `(Arena, stop)` tuple to the `(Arena, start, stop)` block
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# ending at that offset
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self._stop_to_block = {}
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# Map arenas to their `(Arena, start, stop)` blocks in use
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self._allocated_blocks = defaultdict(set)
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self._arenas = []
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# List of pending blocks to free - see comment in free() below
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self._pending_free_blocks = []
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# Statistics
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self._n_mallocs = 0
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self._n_frees = 0
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@staticmethod
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def _roundup(n, alignment):
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# alignment must be a power of 2
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mask = alignment - 1
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return (n + mask) & ~mask
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def _new_arena(self, size):
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# Create a new arena with at least the given *size*
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length = self._roundup(max(self._size, size), mmap.PAGESIZE)
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# We carve larger and larger arenas, for efficiency, until we
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# reach a large-ish size (roughly L3 cache-sized)
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if self._size < self._DOUBLE_ARENA_SIZE_UNTIL:
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self._size *= 2
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util.info('allocating a new mmap of length %d', length)
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arena = Arena(length)
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self._arenas.append(arena)
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return (arena, 0, length)
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def _discard_arena(self, arena):
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# Possibly delete the given (unused) arena
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length = arena.size
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# Reusing an existing arena is faster than creating a new one, so
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# we only reclaim space if it's large enough.
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if length < self._DISCARD_FREE_SPACE_LARGER_THAN:
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return
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blocks = self._allocated_blocks.pop(arena)
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assert not blocks
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del self._start_to_block[(arena, 0)]
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del self._stop_to_block[(arena, length)]
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self._arenas.remove(arena)
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seq = self._len_to_seq[length]
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seq.remove((arena, 0, length))
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if not seq:
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del self._len_to_seq[length]
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self._lengths.remove(length)
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def _malloc(self, size):
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# returns a large enough block -- it might be much larger
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i = bisect.bisect_left(self._lengths, size)
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if i == len(self._lengths):
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return self._new_arena(size)
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else:
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length = self._lengths[i]
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seq = self._len_to_seq[length]
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block = seq.pop()
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if not seq:
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del self._len_to_seq[length], self._lengths[i]
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(arena, start, stop) = block
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del self._start_to_block[(arena, start)]
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del self._stop_to_block[(arena, stop)]
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return block
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def _add_free_block(self, block):
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# make block available and try to merge with its neighbours in the arena
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(arena, start, stop) = block
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try:
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prev_block = self._stop_to_block[(arena, start)]
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except KeyError:
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pass
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else:
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start, _ = self._absorb(prev_block)
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try:
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next_block = self._start_to_block[(arena, stop)]
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except KeyError:
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pass
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else:
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_, stop = self._absorb(next_block)
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block = (arena, start, stop)
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length = stop - start
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try:
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self._len_to_seq[length].append(block)
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except KeyError:
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self._len_to_seq[length] = [block]
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bisect.insort(self._lengths, length)
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self._start_to_block[(arena, start)] = block
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self._stop_to_block[(arena, stop)] = block
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def _absorb(self, block):
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# deregister this block so it can be merged with a neighbour
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(arena, start, stop) = block
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del self._start_to_block[(arena, start)]
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del self._stop_to_block[(arena, stop)]
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length = stop - start
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seq = self._len_to_seq[length]
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seq.remove(block)
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if not seq:
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del self._len_to_seq[length]
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self._lengths.remove(length)
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return start, stop
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def _remove_allocated_block(self, block):
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arena, start, stop = block
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blocks = self._allocated_blocks[arena]
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blocks.remove((start, stop))
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if not blocks:
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# Arena is entirely free, discard it from this process
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self._discard_arena(arena)
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def _free_pending_blocks(self):
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# Free all the blocks in the pending list - called with the lock held.
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while True:
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try:
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block = self._pending_free_blocks.pop()
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except IndexError:
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break
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self._add_free_block(block)
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self._remove_allocated_block(block)
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def free(self, block):
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# free a block returned by malloc()
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# Since free() can be called asynchronously by the GC, it could happen
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# that it's called while self._lock is held: in that case,
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# self._lock.acquire() would deadlock (issue #12352). To avoid that, a
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# trylock is used instead, and if the lock can't be acquired
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# immediately, the block is added to a list of blocks to be freed
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# synchronously sometimes later from malloc() or free(), by calling
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# _free_pending_blocks() (appending and retrieving from a list is not
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# strictly thread-safe but under CPython it's atomic thanks to the GIL).
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if os.getpid() != self._lastpid:
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raise ValueError(
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"My pid ({0:n}) is not last pid {1:n}".format(
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os.getpid(),self._lastpid))
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if not self._lock.acquire(False):
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# can't acquire the lock right now, add the block to the list of
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# pending blocks to free
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self._pending_free_blocks.append(block)
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else:
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# we hold the lock
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try:
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self._n_frees += 1
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self._free_pending_blocks()
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self._add_free_block(block)
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self._remove_allocated_block(block)
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finally:
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self._lock.release()
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def malloc(self, size):
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# return a block of right size (possibly rounded up)
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if size < 0:
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raise ValueError("Size {0:n} out of range".format(size))
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if sys.maxsize <= size:
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raise OverflowError("Size {0:n} too large".format(size))
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if os.getpid() != self._lastpid:
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self.__init__() # reinitialize after fork
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with self._lock:
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self._n_mallocs += 1
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# allow pending blocks to be marked available
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self._free_pending_blocks()
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size = self._roundup(max(size, 1), self._alignment)
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(arena, start, stop) = self._malloc(size)
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real_stop = start + size
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if real_stop < stop:
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# if the returned block is larger than necessary, mark
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# the remainder available
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self._add_free_block((arena, real_stop, stop))
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self._allocated_blocks[arena].add((start, real_stop))
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return (arena, start, real_stop)
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#
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# Class wrapping a block allocated out of a Heap -- can be inherited by child process
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#
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class BufferWrapper(object):
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_heap = Heap()
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def __init__(self, size):
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if size < 0:
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raise ValueError("Size {0:n} out of range".format(size))
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if sys.maxsize <= size:
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raise OverflowError("Size {0:n} too large".format(size))
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block = BufferWrapper._heap.malloc(size)
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self._state = (block, size)
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util.Finalize(self, BufferWrapper._heap.free, args=(block,))
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def create_memoryview(self):
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(arena, start, stop), size = self._state
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return memoryview(arena.buffer)[start:start+size]
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