| # |
| # 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] |
