427 lines
17 KiB
Python
427 lines
17 KiB
Python
# Copyright 2009 Brian Quinlan. All Rights Reserved.
|
|
# Licensed to PSF under a Contributor Agreement.
|
|
|
|
"""Implements ProcessPoolExecutor.
|
|
|
|
The follow diagram and text describe the data-flow through the system:
|
|
|
|
|======================= In-process =====================|== Out-of-process ==|
|
|
|
|
+----------+ +----------+ +--------+ +-----------+ +---------+
|
|
| | => | Work Ids | => | | => | Call Q | => | |
|
|
| | +----------+ | | +-----------+ | |
|
|
| | | ... | | | | ... | | |
|
|
| | | 6 | | | | 5, call() | | |
|
|
| | | 7 | | | | ... | | |
|
|
| Process | | ... | | Local | +-----------+ | Process |
|
|
| Pool | +----------+ | Worker | | #1..n |
|
|
| Executor | | Thread | | |
|
|
| | +----------- + | | +-----------+ | |
|
|
| | <=> | Work Items | <=> | | <= | Result Q | <= | |
|
|
| | +------------+ | | +-----------+ | |
|
|
| | | 6: call() | | | | ... | | |
|
|
| | | future | | | | 4, result | | |
|
|
| | | ... | | | | 3, except | | |
|
|
+----------+ +------------+ +--------+ +-----------+ +---------+
|
|
|
|
Executor.submit() called:
|
|
- creates a uniquely numbered _WorkItem and adds it to the "Work Items" dict
|
|
- adds the id of the _WorkItem to the "Work Ids" queue
|
|
|
|
Local worker thread:
|
|
- reads work ids from the "Work Ids" queue and looks up the corresponding
|
|
WorkItem from the "Work Items" dict: if the work item has been cancelled then
|
|
it is simply removed from the dict, otherwise it is repackaged as a
|
|
_CallItem and put in the "Call Q". New _CallItems are put in the "Call Q"
|
|
until "Call Q" is full. NOTE: the size of the "Call Q" is kept small because
|
|
calls placed in the "Call Q" can no longer be cancelled with Future.cancel().
|
|
- reads _ResultItems from "Result Q", updates the future stored in the
|
|
"Work Items" dict and deletes the dict entry
|
|
|
|
Process #1..n:
|
|
- reads _CallItems from "Call Q", executes the calls, and puts the resulting
|
|
_ResultItems in "Result Q"
|
|
"""
|
|
|
|
__author__ = 'Brian Quinlan (brian@sweetapp.com)'
|
|
|
|
import atexit
|
|
import os
|
|
from concurrent.futures import _base
|
|
import queue
|
|
import multiprocessing
|
|
from multiprocessing.queues import SimpleQueue, Full
|
|
from multiprocessing.connection import wait
|
|
import threading
|
|
import weakref
|
|
|
|
# Workers are created as daemon threads and processes. This is done to allow the
|
|
# interpreter to exit when there are still idle processes in a
|
|
# ProcessPoolExecutor's process pool (i.e. shutdown() was not called). However,
|
|
# allowing workers to die with the interpreter has two undesirable properties:
|
|
# - The workers would still be running during interpretor shutdown,
|
|
# meaning that they would fail in unpredictable ways.
|
|
# - The workers could be killed while evaluating a work item, which could
|
|
# be bad if the callable being evaluated has external side-effects e.g.
|
|
# writing to a file.
|
|
#
|
|
# To work around this problem, an exit handler is installed which tells the
|
|
# workers to exit when their work queues are empty and then waits until the
|
|
# threads/processes finish.
|
|
|
|
_threads_queues = weakref.WeakKeyDictionary()
|
|
_shutdown = False
|
|
|
|
def _python_exit():
|
|
global _shutdown
|
|
_shutdown = True
|
|
items = list(_threads_queues.items())
|
|
for t, q in items:
|
|
q.put(None)
|
|
for t, q in items:
|
|
t.join()
|
|
|
|
# Controls how many more calls than processes will be queued in the call queue.
|
|
# A smaller number will mean that processes spend more time idle waiting for
|
|
# work while a larger number will make Future.cancel() succeed less frequently
|
|
# (Futures in the call queue cannot be cancelled).
|
|
EXTRA_QUEUED_CALLS = 1
|
|
|
|
class _WorkItem(object):
|
|
def __init__(self, future, fn, args, kwargs):
|
|
self.future = future
|
|
self.fn = fn
|
|
self.args = args
|
|
self.kwargs = kwargs
|
|
|
|
class _ResultItem(object):
|
|
def __init__(self, work_id, exception=None, result=None):
|
|
self.work_id = work_id
|
|
self.exception = exception
|
|
self.result = result
|
|
|
|
class _CallItem(object):
|
|
def __init__(self, work_id, fn, args, kwargs):
|
|
self.work_id = work_id
|
|
self.fn = fn
|
|
self.args = args
|
|
self.kwargs = kwargs
|
|
|
|
def _process_worker(call_queue, result_queue):
|
|
"""Evaluates calls from call_queue and places the results in result_queue.
|
|
|
|
This worker is run in a separate process.
|
|
|
|
Args:
|
|
call_queue: A multiprocessing.Queue of _CallItems that will be read and
|
|
evaluated by the worker.
|
|
result_queue: A multiprocessing.Queue of _ResultItems that will written
|
|
to by the worker.
|
|
shutdown: A multiprocessing.Event that will be set as a signal to the
|
|
worker that it should exit when call_queue is empty.
|
|
"""
|
|
while True:
|
|
call_item = call_queue.get(block=True)
|
|
if call_item is None:
|
|
# Wake up queue management thread
|
|
result_queue.put(os.getpid())
|
|
return
|
|
try:
|
|
r = call_item.fn(*call_item.args, **call_item.kwargs)
|
|
except BaseException as e:
|
|
result_queue.put(_ResultItem(call_item.work_id,
|
|
exception=e))
|
|
else:
|
|
result_queue.put(_ResultItem(call_item.work_id,
|
|
result=r))
|
|
|
|
def _add_call_item_to_queue(pending_work_items,
|
|
work_ids,
|
|
call_queue):
|
|
"""Fills call_queue with _WorkItems from pending_work_items.
|
|
|
|
This function never blocks.
|
|
|
|
Args:
|
|
pending_work_items: A dict mapping work ids to _WorkItems e.g.
|
|
{5: <_WorkItem...>, 6: <_WorkItem...>, ...}
|
|
work_ids: A queue.Queue of work ids e.g. Queue([5, 6, ...]). Work ids
|
|
are consumed and the corresponding _WorkItems from
|
|
pending_work_items are transformed into _CallItems and put in
|
|
call_queue.
|
|
call_queue: A multiprocessing.Queue that will be filled with _CallItems
|
|
derived from _WorkItems.
|
|
"""
|
|
while True:
|
|
if call_queue.full():
|
|
return
|
|
try:
|
|
work_id = work_ids.get(block=False)
|
|
except queue.Empty:
|
|
return
|
|
else:
|
|
work_item = pending_work_items[work_id]
|
|
|
|
if work_item.future.set_running_or_notify_cancel():
|
|
call_queue.put(_CallItem(work_id,
|
|
work_item.fn,
|
|
work_item.args,
|
|
work_item.kwargs),
|
|
block=True)
|
|
else:
|
|
del pending_work_items[work_id]
|
|
continue
|
|
|
|
def _queue_management_worker(executor_reference,
|
|
processes,
|
|
pending_work_items,
|
|
work_ids_queue,
|
|
call_queue,
|
|
result_queue):
|
|
"""Manages the communication between this process and the worker processes.
|
|
|
|
This function is run in a local thread.
|
|
|
|
Args:
|
|
executor_reference: A weakref.ref to the ProcessPoolExecutor that owns
|
|
this thread. Used to determine if the ProcessPoolExecutor has been
|
|
garbage collected and that this function can exit.
|
|
process: A list of the multiprocessing.Process instances used as
|
|
workers.
|
|
pending_work_items: A dict mapping work ids to _WorkItems e.g.
|
|
{5: <_WorkItem...>, 6: <_WorkItem...>, ...}
|
|
work_ids_queue: A queue.Queue of work ids e.g. Queue([5, 6, ...]).
|
|
call_queue: A multiprocessing.Queue that will be filled with _CallItems
|
|
derived from _WorkItems for processing by the process workers.
|
|
result_queue: A multiprocessing.Queue of _ResultItems generated by the
|
|
process workers.
|
|
"""
|
|
executor = None
|
|
|
|
def shutting_down():
|
|
return _shutdown or executor is None or executor._shutdown_thread
|
|
|
|
def shutdown_worker():
|
|
# This is an upper bound
|
|
nb_children_alive = sum(p.is_alive() for p in processes.values())
|
|
for i in range(0, nb_children_alive):
|
|
call_queue.put_nowait(None)
|
|
# Release the queue's resources as soon as possible.
|
|
call_queue.close()
|
|
# If .join() is not called on the created processes then
|
|
# some multiprocessing.Queue methods may deadlock on Mac OS X.
|
|
for p in processes.values():
|
|
p.join()
|
|
|
|
reader = result_queue._reader
|
|
|
|
while True:
|
|
_add_call_item_to_queue(pending_work_items,
|
|
work_ids_queue,
|
|
call_queue)
|
|
|
|
sentinels = [p.sentinel for p in processes.values()]
|
|
assert sentinels
|
|
ready = wait([reader] + sentinels)
|
|
if reader in ready:
|
|
result_item = reader.recv()
|
|
else:
|
|
# Mark the process pool broken so that submits fail right now.
|
|
executor = executor_reference()
|
|
if executor is not None:
|
|
executor._broken = True
|
|
executor._shutdown_thread = True
|
|
executor = None
|
|
# All futures in flight must be marked failed
|
|
for work_id, work_item in pending_work_items.items():
|
|
work_item.future.set_exception(
|
|
BrokenProcessPool(
|
|
"A process in the process pool was "
|
|
"terminated abruptly while the future was "
|
|
"running or pending."
|
|
))
|
|
# Delete references to object. See issue16284
|
|
del work_item
|
|
pending_work_items.clear()
|
|
# Terminate remaining workers forcibly: the queues or their
|
|
# locks may be in a dirty state and block forever.
|
|
for p in processes.values():
|
|
p.terminate()
|
|
shutdown_worker()
|
|
return
|
|
if isinstance(result_item, int):
|
|
# Clean shutdown of a worker using its PID
|
|
# (avoids marking the executor broken)
|
|
assert shutting_down()
|
|
p = processes.pop(result_item)
|
|
p.join()
|
|
if not processes:
|
|
shutdown_worker()
|
|
return
|
|
elif result_item is not None:
|
|
work_item = pending_work_items.pop(result_item.work_id, None)
|
|
# work_item can be None if another process terminated (see above)
|
|
if work_item is not None:
|
|
if result_item.exception:
|
|
work_item.future.set_exception(result_item.exception)
|
|
else:
|
|
work_item.future.set_result(result_item.result)
|
|
# Delete references to object. See issue16284
|
|
del work_item
|
|
# Check whether we should start shutting down.
|
|
executor = executor_reference()
|
|
# No more work items can be added if:
|
|
# - The interpreter is shutting down OR
|
|
# - The executor that owns this worker has been collected OR
|
|
# - The executor that owns this worker has been shutdown.
|
|
if shutting_down():
|
|
try:
|
|
# Since no new work items can be added, it is safe to shutdown
|
|
# this thread if there are no pending work items.
|
|
if not pending_work_items:
|
|
shutdown_worker()
|
|
return
|
|
except Full:
|
|
# This is not a problem: we will eventually be woken up (in
|
|
# result_queue.get()) and be able to send a sentinel again.
|
|
pass
|
|
executor = None
|
|
|
|
_system_limits_checked = False
|
|
_system_limited = None
|
|
def _check_system_limits():
|
|
global _system_limits_checked, _system_limited
|
|
if _system_limits_checked:
|
|
if _system_limited:
|
|
raise NotImplementedError(_system_limited)
|
|
_system_limits_checked = True
|
|
try:
|
|
nsems_max = os.sysconf("SC_SEM_NSEMS_MAX")
|
|
except (AttributeError, ValueError):
|
|
# sysconf not available or setting not available
|
|
return
|
|
if nsems_max == -1:
|
|
# indetermined limit, assume that limit is determined
|
|
# by available memory only
|
|
return
|
|
if nsems_max >= 256:
|
|
# minimum number of semaphores available
|
|
# according to POSIX
|
|
return
|
|
_system_limited = "system provides too few semaphores (%d available, 256 necessary)" % nsems_max
|
|
raise NotImplementedError(_system_limited)
|
|
|
|
|
|
class BrokenProcessPool(RuntimeError):
|
|
"""
|
|
Raised when a process in a ProcessPoolExecutor terminated abruptly
|
|
while a future was in the running state.
|
|
"""
|
|
|
|
|
|
class ProcessPoolExecutor(_base.Executor):
|
|
def __init__(self, max_workers=None):
|
|
"""Initializes a new ProcessPoolExecutor instance.
|
|
|
|
Args:
|
|
max_workers: The maximum number of processes that can be used to
|
|
execute the given calls. If None or not given then as many
|
|
worker processes will be created as the machine has processors.
|
|
"""
|
|
_check_system_limits()
|
|
|
|
if max_workers is None:
|
|
self._max_workers = os.cpu_count() or 1
|
|
else:
|
|
self._max_workers = max_workers
|
|
|
|
# Make the call queue slightly larger than the number of processes to
|
|
# prevent the worker processes from idling. But don't make it too big
|
|
# because futures in the call queue cannot be cancelled.
|
|
self._call_queue = multiprocessing.Queue(self._max_workers +
|
|
EXTRA_QUEUED_CALLS)
|
|
# Killed worker processes can produce spurious "broken pipe"
|
|
# tracebacks in the queue's own worker thread. But we detect killed
|
|
# processes anyway, so silence the tracebacks.
|
|
self._call_queue._ignore_epipe = True
|
|
self._result_queue = SimpleQueue()
|
|
self._work_ids = queue.Queue()
|
|
self._queue_management_thread = None
|
|
# Map of pids to processes
|
|
self._processes = {}
|
|
|
|
# Shutdown is a two-step process.
|
|
self._shutdown_thread = False
|
|
self._shutdown_lock = threading.Lock()
|
|
self._broken = False
|
|
self._queue_count = 0
|
|
self._pending_work_items = {}
|
|
|
|
def _start_queue_management_thread(self):
|
|
# When the executor gets lost, the weakref callback will wake up
|
|
# the queue management thread.
|
|
def weakref_cb(_, q=self._result_queue):
|
|
q.put(None)
|
|
if self._queue_management_thread is None:
|
|
# Start the processes so that their sentinels are known.
|
|
self._adjust_process_count()
|
|
self._queue_management_thread = threading.Thread(
|
|
target=_queue_management_worker,
|
|
args=(weakref.ref(self, weakref_cb),
|
|
self._processes,
|
|
self._pending_work_items,
|
|
self._work_ids,
|
|
self._call_queue,
|
|
self._result_queue))
|
|
self._queue_management_thread.daemon = True
|
|
self._queue_management_thread.start()
|
|
_threads_queues[self._queue_management_thread] = self._result_queue
|
|
|
|
def _adjust_process_count(self):
|
|
for _ in range(len(self._processes), self._max_workers):
|
|
p = multiprocessing.Process(
|
|
target=_process_worker,
|
|
args=(self._call_queue,
|
|
self._result_queue))
|
|
p.start()
|
|
self._processes[p.pid] = p
|
|
|
|
def submit(self, fn, *args, **kwargs):
|
|
with self._shutdown_lock:
|
|
if self._broken:
|
|
raise BrokenProcessPool('A child process terminated '
|
|
'abruptly, the process pool is not usable anymore')
|
|
if self._shutdown_thread:
|
|
raise RuntimeError('cannot schedule new futures after shutdown')
|
|
|
|
f = _base.Future()
|
|
w = _WorkItem(f, fn, args, kwargs)
|
|
|
|
self._pending_work_items[self._queue_count] = w
|
|
self._work_ids.put(self._queue_count)
|
|
self._queue_count += 1
|
|
# Wake up queue management thread
|
|
self._result_queue.put(None)
|
|
|
|
self._start_queue_management_thread()
|
|
return f
|
|
submit.__doc__ = _base.Executor.submit.__doc__
|
|
|
|
def shutdown(self, wait=True):
|
|
with self._shutdown_lock:
|
|
self._shutdown_thread = True
|
|
if self._queue_management_thread:
|
|
# Wake up queue management thread
|
|
self._result_queue.put(None)
|
|
if wait:
|
|
self._queue_management_thread.join()
|
|
# To reduce the risk of opening too many files, remove references to
|
|
# objects that use file descriptors.
|
|
self._queue_management_thread = None
|
|
self._call_queue = None
|
|
self._result_queue = None
|
|
self._processes = None
|
|
shutdown.__doc__ = _base.Executor.shutdown.__doc__
|
|
|
|
atexit.register(_python_exit)
|