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queues.py
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# # Module implementing queues # # multiprocessing/queues.py # # Copyright (c) 2006-2008, R Oudkerk # Licensed to PSF under a Contributor Agreement. # __all__ = ['Queue', 'SimpleQueue', 'JoinableQueue'] import sys import os import threading import collections import time import types import weakref import errno from queue import Empty, Full import _multiprocessing from . import connection from . import context _ForkingPickler = context.reduction.ForkingPickler from .util import debug, info, Finalize, register_after_fork, is_exiting # # Queue type using a pipe, buffer and thread # class Queue(object): def __init__(self, maxsize=0, *, ctx): if maxsize <= 0: # Can raise ImportError (see issues #3770 and #23400) from .synchronize import SEM_VALUE_MAX as maxsize self._maxsize = maxsize self._reader, self._writer = connection.Pipe(duplex=False) self._rlock = ctx.Lock() self._opid = os.getpid() if sys.platform == 'win32': self._wlock = None else: self._wlock = ctx.Lock() self._sem = ctx.BoundedSemaphore(maxsize) # For use by concurrent.futures self._ignore_epipe = False self._reset() if sys.platform != 'win32': register_after_fork(self, Queue._after_fork) def __getstate__(self): context.assert_spawning(self) return (self._ignore_epipe, self._maxsize, self._reader, self._writer, self._rlock, self._wlock, self._sem, self._opid) def __setstate__(self, state): (self._ignore_epipe, self._maxsize, self._reader, self._writer, self._rlock, self._wlock, self._sem, self._opid) = state self._reset() def _after_fork(self): debug('Queue._after_fork()') self._reset(after_fork=True) def _reset(self, after_fork=False): if after_fork: self._notempty._at_fork_reinit() else: self._notempty = threading.Condition(threading.Lock()) self._buffer = collections.deque() self._thread = None self._jointhread = None self._joincancelled = False self._closed = False self._close = None self._send_bytes = self._writer.send_bytes self._recv_bytes = self._reader.recv_bytes self._poll = self._reader.poll def put(self, obj, block=True, timeout=None): if self._closed: raise ValueError(f"Queue {self!r} is closed") if not self._sem.acquire(block, timeout): raise Full with self._notempty: if self._thread is None: self._start_thread() self._buffer.append(obj) self._notempty.notify() def get(self, block=True, timeout=None): if self._closed: raise ValueError(f"Queue {self!r} is closed") if block and timeout is None: with self._rlock: res = self._recv_bytes() self._sem.release() else: if block: deadline = time.monotonic() + timeout if not self._rlock.acquire(block, timeout): raise Empty try: if block: timeout = deadline - time.monotonic() if not self._poll(timeout): raise Empty elif not self._poll(): raise Empty res = self._recv_bytes() self._sem.release() finally: self._rlock.release() # unserialize the data after having released the lock return _ForkingPickler.loads(res) def qsize(self): # Raises NotImplementedError on Mac OSX because of broken sem_getvalue() return self._maxsize - self._sem._semlock._get_value() def empty(self): return not self._poll() def full(self): return self._sem._semlock._is_zero() def get_nowait(self): return self.get(False) def put_nowait(self, obj): return self.put(obj, False) def close(self): self._closed = True try: self._reader.close() finally: close = self._close if close: self._close = None close() def join_thread(self): debug('Queue.join_thread()') assert self._closed, "Queue {0!r} not closed".format(self) if self._jointhread: self._jointhread() def cancel_join_thread(self): debug('Queue.cancel_join_thread()') self._joincancelled = True try: self._jointhread.cancel() except AttributeError: pass def _start_thread(self): debug('Queue._start_thread()') # Start thread which transfers data from buffer to pipe self._buffer.clear() self._thread = threading.Thread( target=Queue._feed, args=(self._buffer, self._notempty, self._send_bytes, self._wlock, self._writer.close, self._ignore_epipe, self._on_queue_feeder_error, self._sem), name='QueueFeederThread' ) self._thread.daemon = True debug('doing self._thread.start()') self._thread.start() debug('... done self._thread.start()') if not self._joincancelled: self._jointhread = Finalize( self._thread, Queue._finalize_join, [weakref.ref(self._thread)], exitpriority=-5 ) # Send sentinel to the thread queue object when garbage collected self._close = Finalize( self, Queue._finalize_close, [self._buffer, self._notempty], exitpriority=10 ) @staticmethod def _finalize_join(twr): debug('joining queue thread') thread = twr() if thread is not None: thread.join() debug('... queue thread joined') else: debug('... queue thread already dead') @staticmethod def _finalize_close(buffer, notempty): debug('telling queue thread to quit') with notempty: buffer.append(_sentinel) notempty.notify() @staticmethod def _feed(buffer, notempty, send_bytes, writelock, close, ignore_epipe, onerror, queue_sem): debug('starting thread to feed data to pipe') nacquire = notempty.acquire nrelease = notempty.release nwait = notempty.wait bpopleft = buffer.popleft sentinel = _sentinel if sys.platform != 'win32': wacquire = writelock.acquire wrelease = writelock.release else: wacquire = None while 1: try: nacquire() try: if not buffer: nwait() finally: nrelease() try: while 1: obj = bpopleft() if obj is sentinel: debug('feeder thread got sentinel -- exiting') close() return # serialize the data before acquiring the lock obj = _ForkingPickler.dumps(obj) if wacquire is None: send_bytes(obj) else: wacquire() try: send_bytes(obj) finally: wrelease() except IndexError: pass except Exception as e: if ignore_epipe and getattr(e, 'errno', 0) == errno.EPIPE: return # Since this runs in a daemon thread the resources it uses # may be become unusable while the process is cleaning up. # We ignore errors which happen after the process has # started to cleanup. if is_exiting(): info('error in queue thread: %s', e) return else: # Since the object has not been sent in the queue, we need # to decrease the size of the queue. The error acts as # if the object had been silently removed from the queue # and this step is necessary to have a properly working # queue. queue_sem.release() onerror(e, obj) @staticmethod def _on_queue_feeder_error(e, obj): """ Private API hook called when feeding data in the background thread raises an exception. For overriding by concurrent.futures. """ import traceback traceback.print_exc() _sentinel = object() # # A queue type which also supports join() and task_done() methods # # Note that if you do not call task_done() for each finished task then # eventually the counter's semaphore may overflow causing Bad Things # to happen. # class JoinableQueue(Queue): def __init__(self, maxsize=0, *, ctx): Queue.__init__(self, maxsize, ctx=ctx) self._unfinished_tasks = ctx.Semaphore(0) self._cond = ctx.Condition() def __getstate__(self): return Queue.__getstate__(self) + (self._cond, self._unfinished_tasks) def __setstate__(self, state): Queue.__setstate__(self, state[:-2]) self._cond, self._unfinished_tasks = state[-2:] def put(self, obj, block=True, timeout=None): if self._closed: raise ValueError(f"Queue {self!r} is closed") if not self._sem.acquire(block, timeout): raise Full with self._notempty, self._cond: if self._thread is None: self._start_thread() self._buffer.append(obj) self._unfinished_tasks.release() self._notempty.notify() def task_done(self): with self._cond: if not self._unfinished_tasks.acquire(False): raise ValueError('task_done() called too many times') if self._unfinished_tasks._semlock._is_zero(): self._cond.notify_all() def join(self): with self._cond: if not self._unfinished_tasks._semlock._is_zero(): self._cond.wait() # # Simplified Queue type -- really just a locked pipe # class SimpleQueue(object): def __init__(self, *, ctx): self._reader, self._writer = connection.Pipe(duplex=False) self._rlock = ctx.Lock() self._poll = self._reader.poll if sys.platform == 'win32': self._wlock = None else: self._wlock = ctx.Lock() def close(self): self._reader.close() self._writer.close() def empty(self): return not self._poll() def __getstate__(self): context.assert_spawning(self) return (self._reader, self._writer, self._rlock, self._wlock) def __setstate__(self, state): (self._reader, self._writer, self._rlock, self._wlock) = state self._poll = self._reader.poll def get(self): with self._rlock: res = self._reader.recv_bytes() # unserialize the data after having released the lock return _ForkingPickler.loads(res) def put(self, obj): # serialize the data before acquiring the lock obj = _ForkingPickler.dumps(obj) if self._wlock is None: # writes to a message oriented win32 pipe are atomic self._writer.send_bytes(obj) else: with self._wlock: self._writer.send_bytes(obj) __class_getitem__ = classmethod(types.GenericAlias)