view mercurial/thirdparty/concurrent/futures/thread.py @ 37623:eb687c28a915

thirdparty: vendor futures 3.2.0

Python 3 has a concurrent.futures package in the standard library
for representing futures. The "futures" package on PyPI is a backport
of this package to work with Python 2.

The wire protocol code today has its own future concept for handling
of "batch" requests. The frame-based protocol will also want to
use futures.

I've heavily used the "futures" package on Python 2 in other projects
and it is pretty nice. It even has a built-in thread and process pool
for running functions in parallel. I've used this heavily for concurrent
I/O and other GIL-less activities.

The existing futures API in the wire protocol code is not as nice as
concurrent.futures. Since concurrent.futures is in the Python standard
library and will presumably be the long-term future for futures in our
code base, let's vendor the backport so we can use proper futures today.

# no-check-commit because of style violations

Differential Revision: https://phab.mercurial-scm.org/D3261

# Copyright 2009 Brian Quinlan. All Rights Reserved.
# Licensed to PSF under a Contributor Agreement.

"""Implements ThreadPoolExecutor."""

import atexit
from concurrent.futures import _base
import itertools
import Queue as queue
import threading
import weakref
import sys

try:
    from multiprocessing import cpu_count
except ImportError:
    # some platforms don't have multiprocessing
    def cpu_count():
        return None

__author__ = 'Brian Quinlan ([e-mail])'

# Workers are created as daemon threads. This is done to allow the interpreter
# to exit when there are still idle threads in a ThreadPoolExecutor's thread
# 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 finish.

_threads_queues = weakref.WeakKeyDictionary()
_shutdown = False

def _python_exit():
    global _shutdown
    _shutdown = True
    items = list(_threads_queues.items()) if _threads_queues else ()
    for t, q in items:
        q.put(None)
    for t, q in items:
        t.join(sys.maxint)

atexit.register(_python_exit)

class _WorkItem(object):
    def __init__(self, future, fn, args, kwargs):
        self.future = future
        self.fn = fn
        self.args = args
        self.kwargs = kwargs

    def run(self):
        if not self.future.set_running_or_notify_cancel():
            return

        try:
            result = self.fn(*self.args, **self.kwargs)
        except:
            e, tb = sys.exc_info()[1:]
            self.future.set_exception_info(e, tb)
        else:
            self.future.set_result(result)

def _worker(executor_reference, work_queue):
    try:
        while True:
            work_item = work_queue.get(block=True)
            if work_item is not None:
                work_item.run()
                # Delete references to object. See issue16284
                del work_item
                continue
            executor = executor_reference()
            # Exit if:
            #   - The interpreter is shutting down OR
            #   - The executor that owns the worker has been collected OR
            #   - The executor that owns the worker has been shutdown.
            if _shutdown or executor is None or executor._shutdown:
                # Notice other workers
                work_queue.put(None)
                return
            del executor
    except:
        _base.LOGGER.critical('Exception in worker', exc_info=True)


class ThreadPoolExecutor(_base.Executor):

    # Used to assign unique thread names when thread_name_prefix is not supplied.
    _counter = itertools.count().next

    def __init__(self, max_workers=None, thread_name_prefix=''):
        """Initializes a new ThreadPoolExecutor instance.

        Args:
            max_workers: The maximum number of threads that can be used to
                execute the given calls.
            thread_name_prefix: An optional name prefix to give our threads.
        """
        if max_workers is None:
            # Use this number because ThreadPoolExecutor is often
            # used to overlap I/O instead of CPU work.
            max_workers = (cpu_count() or 1) * 5
        if max_workers <= 0:
            raise ValueError("max_workers must be greater than 0")

        self._max_workers = max_workers
        self._work_queue = queue.Queue()
        self._threads = set()
        self._shutdown = False
        self._shutdown_lock = threading.Lock()
        self._thread_name_prefix = (thread_name_prefix or
                                    ("ThreadPoolExecutor-%d" % self._counter()))

    def submit(self, fn, *args, **kwargs):
        with self._shutdown_lock:
            if self._shutdown:
                raise RuntimeError('cannot schedule new futures after shutdown')

            f = _base.Future()
            w = _WorkItem(f, fn, args, kwargs)

            self._work_queue.put(w)
            self._adjust_thread_count()
            return f
    submit.__doc__ = _base.Executor.submit.__doc__

    def _adjust_thread_count(self):
        # When the executor gets lost, the weakref callback will wake up
        # the worker threads.
        def weakref_cb(_, q=self._work_queue):
            q.put(None)
        # TODO(bquinlan): Should avoid creating new threads if there are more
        # idle threads than items in the work queue.
        num_threads = len(self._threads)
        if num_threads < self._max_workers:
            thread_name = '%s_%d' % (self._thread_name_prefix or self,
                                     num_threads)
            t = threading.Thread(name=thread_name, target=_worker,
                                 args=(weakref.ref(self, weakref_cb),
                                       self._work_queue))
            t.daemon = True
            t.start()
            self._threads.add(t)
            _threads_queues[t] = self._work_queue

    def shutdown(self, wait=True):
        with self._shutdown_lock:
            self._shutdown = True
            self._work_queue.put(None)
        if wait:
            for t in self._threads:
                t.join(sys.maxint)
    shutdown.__doc__ = _base.Executor.shutdown.__doc__