Class Heap

Lib/multiprocessing/heap.py:115–316

#

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