indygreg created this revision.
Herald added a subscriber: mercurial-devel.
Herald added a reviewer: hg-reviewers.

REVISION SUMMARY
  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.
  
  1. no-check-commit because of style violations

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D3261

AFFECTED FILES
  mercurial/thirdparty/concurrent/LICENSE
  mercurial/thirdparty/concurrent/__init__.py
  mercurial/thirdparty/concurrent/futures/__init__.py
  mercurial/thirdparty/concurrent/futures/_base.py
  mercurial/thirdparty/concurrent/futures/process.py
  mercurial/thirdparty/concurrent/futures/thread.py

CHANGE DETAILS

diff --git a/mercurial/thirdparty/concurrent/futures/thread.py 
b/mercurial/thirdparty/concurrent/futures/thread.py
new file mode 100644
--- /dev/null
+++ b/mercurial/thirdparty/concurrent/futures/thread.py
@@ -0,0 +1,160 @@
+# 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 (br...@sweetapp.com)'
+
+# 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__
diff --git a/mercurial/thirdparty/concurrent/futures/process.py 
b/mercurial/thirdparty/concurrent/futures/process.py
new file mode 100644
--- /dev/null
+++ b/mercurial/thirdparty/concurrent/futures/process.py
@@ -0,0 +1,363 @@
+# 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 "Request Q"
+"""
+
+import atexit
+from concurrent.futures import _base
+import Queue as queue
+import multiprocessing
+import threading
+import weakref
+import sys
+
+__author__ = 'Brian Quinlan (br...@sweetapp.com)'
+
+# 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()) if _threads_queues else ()
+    for t, q in items:
+        q.put(None)
+    for t, q in items:
+        t.join(sys.maxint)
+
+# 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(None)
+            return
+        try:
+            r = call_item.fn(*call_item.args, **call_item.kwargs)
+        except:
+            e = sys.exc_info()[1]
+            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.
+    """
+    nb_shutdown_processes = [0]
+    def shutdown_one_process():
+        """Tell a worker to terminate, which will in turn wake us again"""
+        call_queue.put(None)
+        nb_shutdown_processes[0] += 1
+    while True:
+        _add_call_item_to_queue(pending_work_items,
+                                work_ids_queue,
+                                call_queue)
+
+        result_item = result_queue.get(block=True)
+        if result_item is not None:
+            work_item = pending_work_items[result_item.work_id]
+            del pending_work_items[result_item.work_id]
+
+            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 _shutdown or executor is None or executor._shutdown_thread:
+            # 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:
+                while nb_shutdown_processes[0] < len(processes):
+                    shutdown_one_process()
+                # If .join() is not called on the created processes then
+                # some multiprocessing.Queue methods may deadlock on Mac OS
+                # X.
+                for p in processes:
+                    p.join()
+                call_queue.close()
+                return
+        del executor
+
+_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:
+        import os
+        nsems_max = os.sysconf("SC_SEM_NSEMS_MAX")
+    except (AttributeError, ValueError):
+        # sysconf not available or setting not available
+        return
+    if nsems_max == -1:
+        # indetermine 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 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 = multiprocessing.cpu_count()
+        else:
+            if max_workers <= 0:
+                raise ValueError("max_workers must be greater than 0")
+
+            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)
+        self._result_queue = multiprocessing.Queue()
+        self._work_ids = queue.Queue()
+        self._queue_management_thread = None
+        self._processes = set()
+
+        # Shutdown is a two-step process.
+        self._shutdown_thread = False
+        self._shutdown_lock = threading.Lock()
+        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:
+            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.add(p)
+
+    def submit(self, fn, *args, **kwargs):
+        with self._shutdown_lock:
+            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()
+            self._adjust_process_count()
+            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(sys.maxint)
+        # To reduce the risk of openning 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)
diff --git a/mercurial/thirdparty/concurrent/futures/_base.py 
b/mercurial/thirdparty/concurrent/futures/_base.py
new file mode 100644
--- /dev/null
+++ b/mercurial/thirdparty/concurrent/futures/_base.py
@@ -0,0 +1,667 @@
+# Copyright 2009 Brian Quinlan. All Rights Reserved.
+# Licensed to PSF under a Contributor Agreement.
+
+import collections
+import logging
+import threading
+import itertools
+import time
+import types
+
+__author__ = 'Brian Quinlan (br...@sweetapp.com)'
+
+FIRST_COMPLETED = 'FIRST_COMPLETED'
+FIRST_EXCEPTION = 'FIRST_EXCEPTION'
+ALL_COMPLETED = 'ALL_COMPLETED'
+_AS_COMPLETED = '_AS_COMPLETED'
+
+# Possible future states (for internal use by the futures package).
+PENDING = 'PENDING'
+RUNNING = 'RUNNING'
+# The future was cancelled by the user...
+CANCELLED = 'CANCELLED'
+# ...and _Waiter.add_cancelled() was called by a worker.
+CANCELLED_AND_NOTIFIED = 'CANCELLED_AND_NOTIFIED'
+FINISHED = 'FINISHED'
+
+_FUTURE_STATES = [
+    PENDING,
+    RUNNING,
+    CANCELLED,
+    CANCELLED_AND_NOTIFIED,
+    FINISHED
+]
+
+_STATE_TO_DESCRIPTION_MAP = {
+    PENDING: "pending",
+    RUNNING: "running",
+    CANCELLED: "cancelled",
+    CANCELLED_AND_NOTIFIED: "cancelled",
+    FINISHED: "finished"
+}
+
+# Logger for internal use by the futures package.
+LOGGER = logging.getLogger("concurrent.futures")
+
+class Error(Exception):
+    """Base class for all future-related exceptions."""
+    pass
+
+class CancelledError(Error):
+    """The Future was cancelled."""
+    pass
+
+class TimeoutError(Error):
+    """The operation exceeded the given deadline."""
+    pass
+
+class _Waiter(object):
+    """Provides the event that wait() and as_completed() block on."""
+    def __init__(self):
+        self.event = threading.Event()
+        self.finished_futures = []
+
+    def add_result(self, future):
+        self.finished_futures.append(future)
+
+    def add_exception(self, future):
+        self.finished_futures.append(future)
+
+    def add_cancelled(self, future):
+        self.finished_futures.append(future)
+
+class _AsCompletedWaiter(_Waiter):
+    """Used by as_completed()."""
+
+    def __init__(self):
+        super(_AsCompletedWaiter, self).__init__()
+        self.lock = threading.Lock()
+
+    def add_result(self, future):
+        with self.lock:
+            super(_AsCompletedWaiter, self).add_result(future)
+            self.event.set()
+
+    def add_exception(self, future):
+        with self.lock:
+            super(_AsCompletedWaiter, self).add_exception(future)
+            self.event.set()
+
+    def add_cancelled(self, future):
+        with self.lock:
+            super(_AsCompletedWaiter, self).add_cancelled(future)
+            self.event.set()
+
+class _FirstCompletedWaiter(_Waiter):
+    """Used by wait(return_when=FIRST_COMPLETED)."""
+
+    def add_result(self, future):
+        super(_FirstCompletedWaiter, self).add_result(future)
+        self.event.set()
+
+    def add_exception(self, future):
+        super(_FirstCompletedWaiter, self).add_exception(future)
+        self.event.set()
+
+    def add_cancelled(self, future):
+        super(_FirstCompletedWaiter, self).add_cancelled(future)
+        self.event.set()
+
+class _AllCompletedWaiter(_Waiter):
+    """Used by wait(return_when=FIRST_EXCEPTION and ALL_COMPLETED)."""
+
+    def __init__(self, num_pending_calls, stop_on_exception):
+        self.num_pending_calls = num_pending_calls
+        self.stop_on_exception = stop_on_exception
+        self.lock = threading.Lock()
+        super(_AllCompletedWaiter, self).__init__()
+
+    def _decrement_pending_calls(self):
+        with self.lock:
+            self.num_pending_calls -= 1
+            if not self.num_pending_calls:
+                self.event.set()
+
+    def add_result(self, future):
+        super(_AllCompletedWaiter, self).add_result(future)
+        self._decrement_pending_calls()
+
+    def add_exception(self, future):
+        super(_AllCompletedWaiter, self).add_exception(future)
+        if self.stop_on_exception:
+            self.event.set()
+        else:
+            self._decrement_pending_calls()
+
+    def add_cancelled(self, future):
+        super(_AllCompletedWaiter, self).add_cancelled(future)
+        self._decrement_pending_calls()
+
+class _AcquireFutures(object):
+    """A context manager that does an ordered acquire of Future conditions."""
+
+    def __init__(self, futures):
+        self.futures = sorted(futures, key=id)
+
+    def __enter__(self):
+        for future in self.futures:
+            future._condition.acquire()
+
+    def __exit__(self, *args):
+        for future in self.futures:
+            future._condition.release()
+
+def _create_and_install_waiters(fs, return_when):
+    if return_when == _AS_COMPLETED:
+        waiter = _AsCompletedWaiter()
+    elif return_when == FIRST_COMPLETED:
+        waiter = _FirstCompletedWaiter()
+    else:
+        pending_count = sum(
+                f._state not in [CANCELLED_AND_NOTIFIED, FINISHED] for f in fs)
+
+        if return_when == FIRST_EXCEPTION:
+            waiter = _AllCompletedWaiter(pending_count, stop_on_exception=True)
+        elif return_when == ALL_COMPLETED:
+            waiter = _AllCompletedWaiter(pending_count, 
stop_on_exception=False)
+        else:
+            raise ValueError("Invalid return condition: %r" % return_when)
+
+    for f in fs:
+        f._waiters.append(waiter)
+
+    return waiter
+
+
+def _yield_finished_futures(fs, waiter, ref_collect):
+    """
+    Iterate on the list *fs*, yielding finished futures one by one in
+    reverse order.
+    Before yielding a future, *waiter* is removed from its waiters
+    and the future is removed from each set in the collection of sets
+    *ref_collect*.
+
+    The aim of this function is to avoid keeping stale references after
+    the future is yielded and before the iterator resumes.
+    """
+    while fs:
+        f = fs[-1]
+        for futures_set in ref_collect:
+            futures_set.remove(f)
+        with f._condition:
+            f._waiters.remove(waiter)
+        del f
+        # Careful not to keep a reference to the popped value
+        yield fs.pop()
+
+
+def as_completed(fs, timeout=None):
+    """An iterator over the given futures that yields each as it completes.
+
+    Args:
+        fs: The sequence of Futures (possibly created by different Executors) 
to
+            iterate over.
+        timeout: The maximum number of seconds to wait. If None, then there
+            is no limit on the wait time.
+
+    Returns:
+        An iterator that yields the given Futures as they complete (finished or
+        cancelled). If any given Futures are duplicated, they will be returned
+        once.
+
+    Raises:
+        TimeoutError: If the entire result iterator could not be generated
+            before the given timeout.
+    """
+    if timeout is not None:
+        end_time = timeout + time.time()
+
+    fs = set(fs)
+    total_futures = len(fs)
+    with _AcquireFutures(fs):
+        finished = set(
+                f for f in fs
+                if f._state in [CANCELLED_AND_NOTIFIED, FINISHED])
+        pending = fs - finished
+        waiter = _create_and_install_waiters(fs, _AS_COMPLETED)
+    finished = list(finished)
+    try:
+        for f in _yield_finished_futures(finished, waiter,
+                                         ref_collect=(fs,)):
+            f = [f]
+            yield f.pop()
+
+        while pending:
+            if timeout is None:
+                wait_timeout = None
+            else:
+                wait_timeout = end_time - time.time()
+                if wait_timeout < 0:
+                    raise TimeoutError(
+                            '%d (of %d) futures unfinished' % (
+                            len(pending), total_futures))
+
+            waiter.event.wait(wait_timeout)
+
+            with waiter.lock:
+                finished = waiter.finished_futures
+                waiter.finished_futures = []
+                waiter.event.clear()
+
+            # reverse to keep finishing order
+            finished.reverse()
+            for f in _yield_finished_futures(finished, waiter,
+                                             ref_collect=(fs, pending)):
+                f = [f]
+                yield f.pop()
+
+    finally:
+        # Remove waiter from unfinished futures
+        for f in fs:
+            with f._condition:
+                f._waiters.remove(waiter)
+
+DoneAndNotDoneFutures = collections.namedtuple(
+        'DoneAndNotDoneFutures', 'done not_done')
+def wait(fs, timeout=None, return_when=ALL_COMPLETED):
+    """Wait for the futures in the given sequence to complete.
+
+    Args:
+        fs: The sequence of Futures (possibly created by different Executors) 
to
+            wait upon.
+        timeout: The maximum number of seconds to wait. If None, then there
+            is no limit on the wait time.
+        return_when: Indicates when this function should return. The options
+            are:
+
+            FIRST_COMPLETED - Return when any future finishes or is
+                              cancelled.
+            FIRST_EXCEPTION - Return when any future finishes by raising an
+                              exception. If no future raises an exception
+                              then it is equivalent to ALL_COMPLETED.
+            ALL_COMPLETED -   Return when all futures finish or are cancelled.
+
+    Returns:
+        A named 2-tuple of sets. The first set, named 'done', contains the
+        futures that completed (is finished or cancelled) before the wait
+        completed. The second set, named 'not_done', contains uncompleted
+        futures.
+    """
+    with _AcquireFutures(fs):
+        done = set(f for f in fs
+                   if f._state in [CANCELLED_AND_NOTIFIED, FINISHED])
+        not_done = set(fs) - done
+
+        if (return_when == FIRST_COMPLETED) and done:
+            return DoneAndNotDoneFutures(done, not_done)
+        elif (return_when == FIRST_EXCEPTION) and done:
+            if any(f for f in done
+                   if not f.cancelled() and f.exception() is not None):
+                return DoneAndNotDoneFutures(done, not_done)
+
+        if len(done) == len(fs):
+            return DoneAndNotDoneFutures(done, not_done)
+
+        waiter = _create_and_install_waiters(fs, return_when)
+
+    waiter.event.wait(timeout)
+    for f in fs:
+        with f._condition:
+            f._waiters.remove(waiter)
+
+    done.update(waiter.finished_futures)
+    return DoneAndNotDoneFutures(done, set(fs) - done)
+
+class Future(object):
+    """Represents the result of an asynchronous computation."""
+
+    def __init__(self):
+        """Initializes the future. Should not be called by clients."""
+        self._condition = threading.Condition()
+        self._state = PENDING
+        self._result = None
+        self._exception = None
+        self._traceback = None
+        self._waiters = []
+        self._done_callbacks = []
+
+    def _invoke_callbacks(self):
+        for callback in self._done_callbacks:
+            try:
+                callback(self)
+            except Exception:
+                LOGGER.exception('exception calling callback for %r', self)
+            except BaseException:
+                # Explicitly let all other new-style exceptions through so
+                # that we can catch all old-style exceptions with a simple
+                # "except:" clause below.
+                #
+                # All old-style exception objects are instances of
+                # types.InstanceType, but "except types.InstanceType:" does
+                # not catch old-style exceptions for some reason.  Thus, the
+                # only way to catch all old-style exceptions without catching
+                # any new-style exceptions is to filter out the new-style
+                # exceptions, which all derive from BaseException.
+                raise
+            except:
+                # Because of the BaseException clause above, this handler only
+                # executes for old-style exception objects.
+                LOGGER.exception('exception calling callback for %r', self)
+
+    def __repr__(self):
+        with self._condition:
+            if self._state == FINISHED:
+                if self._exception:
+                    return '<%s at %#x state=%s raised %s>' % (
+                        self.__class__.__name__,
+                        id(self),
+                        _STATE_TO_DESCRIPTION_MAP[self._state],
+                        self._exception.__class__.__name__)
+                else:
+                    return '<%s at %#x state=%s returned %s>' % (
+                        self.__class__.__name__,
+                        id(self),
+                        _STATE_TO_DESCRIPTION_MAP[self._state],
+                        self._result.__class__.__name__)
+            return '<%s at %#x state=%s>' % (
+                    self.__class__.__name__,
+                    id(self),
+                   _STATE_TO_DESCRIPTION_MAP[self._state])
+
+    def cancel(self):
+        """Cancel the future if possible.
+
+        Returns True if the future was cancelled, False otherwise. A future
+        cannot be cancelled if it is running or has already completed.
+        """
+        with self._condition:
+            if self._state in [RUNNING, FINISHED]:
+                return False
+
+            if self._state in [CANCELLED, CANCELLED_AND_NOTIFIED]:
+                return True
+
+            self._state = CANCELLED
+            self._condition.notify_all()
+
+        self._invoke_callbacks()
+        return True
+
+    def cancelled(self):
+        """Return True if the future was cancelled."""
+        with self._condition:
+            return self._state in [CANCELLED, CANCELLED_AND_NOTIFIED]
+
+    def running(self):
+        """Return True if the future is currently executing."""
+        with self._condition:
+            return self._state == RUNNING
+
+    def done(self):
+        """Return True of the future was cancelled or finished executing."""
+        with self._condition:
+            return self._state in [CANCELLED, CANCELLED_AND_NOTIFIED, FINISHED]
+
+    def __get_result(self):
+        if self._exception:
+            if isinstance(self._exception, types.InstanceType):
+                # The exception is an instance of an old-style class, which
+                # means type(self._exception) returns types.ClassType instead
+                # of the exception's actual class type.
+                exception_type = self._exception.__class__
+            else:
+                exception_type = type(self._exception)
+            raise exception_type, self._exception, self._traceback
+        else:
+            return self._result
+
+    def add_done_callback(self, fn):
+        """Attaches a callable that will be called when the future finishes.
+
+        Args:
+            fn: A callable that will be called with this future as its only
+                argument when the future completes or is cancelled. The 
callable
+                will always be called by a thread in the same process in which
+                it was added. If the future has already completed or been
+                cancelled then the callable will be called immediately. These
+                callables are called in the order that they were added.
+        """
+        with self._condition:
+            if self._state not in [CANCELLED, CANCELLED_AND_NOTIFIED, 
FINISHED]:
+                self._done_callbacks.append(fn)
+                return
+        fn(self)
+
+    def result(self, timeout=None):
+        """Return the result of the call that the future represents.
+
+        Args:
+            timeout: The number of seconds to wait for the result if the future
+                isn't done. If None, then there is no limit on the wait time.
+
+        Returns:
+            The result of the call that the future represents.
+
+        Raises:
+            CancelledError: If the future was cancelled.
+            TimeoutError: If the future didn't finish executing before the 
given
+                timeout.
+            Exception: If the call raised then that exception will be raised.
+        """
+        with self._condition:
+            if self._state in [CANCELLED, CANCELLED_AND_NOTIFIED]:
+                raise CancelledError()
+            elif self._state == FINISHED:
+                return self.__get_result()
+
+            self._condition.wait(timeout)
+
+            if self._state in [CANCELLED, CANCELLED_AND_NOTIFIED]:
+                raise CancelledError()
+            elif self._state == FINISHED:
+                return self.__get_result()
+            else:
+                raise TimeoutError()
+
+    def exception_info(self, timeout=None):
+        """Return a tuple of (exception, traceback) raised by the call that the
+        future represents.
+
+        Args:
+            timeout: The number of seconds to wait for the exception if the
+                future isn't done. If None, then there is no limit on the wait
+                time.
+
+        Returns:
+            The exception raised by the call that the future represents or None
+            if the call completed without raising.
+
+        Raises:
+            CancelledError: If the future was cancelled.
+            TimeoutError: If the future didn't finish executing before the 
given
+                timeout.
+        """
+        with self._condition:
+            if self._state in [CANCELLED, CANCELLED_AND_NOTIFIED]:
+                raise CancelledError()
+            elif self._state == FINISHED:
+                return self._exception, self._traceback
+
+            self._condition.wait(timeout)
+
+            if self._state in [CANCELLED, CANCELLED_AND_NOTIFIED]:
+                raise CancelledError()
+            elif self._state == FINISHED:
+                return self._exception, self._traceback
+            else:
+                raise TimeoutError()
+
+    def exception(self, timeout=None):
+        """Return the exception raised by the call that the future represents.
+
+        Args:
+            timeout: The number of seconds to wait for the exception if the
+                future isn't done. If None, then there is no limit on the wait
+                time.
+
+        Returns:
+            The exception raised by the call that the future represents or None
+            if the call completed without raising.
+
+        Raises:
+            CancelledError: If the future was cancelled.
+            TimeoutError: If the future didn't finish executing before the 
given
+                timeout.
+        """
+        return self.exception_info(timeout)[0]
+
+    # The following methods should only be used by Executors and in tests.
+    def set_running_or_notify_cancel(self):
+        """Mark the future as running or process any cancel notifications.
+
+        Should only be used by Executor implementations and unit tests.
+
+        If the future has been cancelled (cancel() was called and returned
+        True) then any threads waiting on the future completing (though calls
+        to as_completed() or wait()) are notified and False is returned.
+
+        If the future was not cancelled then it is put in the running state
+        (future calls to running() will return True) and True is returned.
+
+        This method should be called by Executor implementations before
+        executing the work associated with this future. If this method returns
+        False then the work should not be executed.
+
+        Returns:
+            False if the Future was cancelled, True otherwise.
+
+        Raises:
+            RuntimeError: if this method was already called or if set_result()
+                or set_exception() was called.
+        """
+        with self._condition:
+            if self._state == CANCELLED:
+                self._state = CANCELLED_AND_NOTIFIED
+                for waiter in self._waiters:
+                    waiter.add_cancelled(self)
+                # self._condition.notify_all() is not necessary because
+                # self.cancel() triggers a notification.
+                return False
+            elif self._state == PENDING:
+                self._state = RUNNING
+                return True
+            else:
+                LOGGER.critical('Future %s in unexpected state: %s',
+                                id(self),
+                                self._state)
+                raise RuntimeError('Future in unexpected state')
+
+    def set_result(self, result):
+        """Sets the return value of work associated with the future.
+
+        Should only be used by Executor implementations and unit tests.
+        """
+        with self._condition:
+            self._result = result
+            self._state = FINISHED
+            for waiter in self._waiters:
+                waiter.add_result(self)
+            self._condition.notify_all()
+        self._invoke_callbacks()
+
+    def set_exception_info(self, exception, traceback):
+        """Sets the result of the future as being the given exception
+        and traceback.
+
+        Should only be used by Executor implementations and unit tests.
+        """
+        with self._condition:
+            self._exception = exception
+            self._traceback = traceback
+            self._state = FINISHED
+            for waiter in self._waiters:
+                waiter.add_exception(self)
+            self._condition.notify_all()
+        self._invoke_callbacks()
+
+    def set_exception(self, exception):
+        """Sets the result of the future as being the given exception.
+
+        Should only be used by Executor implementations and unit tests.
+        """
+        self.set_exception_info(exception, None)
+
+class Executor(object):
+    """This is an abstract base class for concrete asynchronous executors."""
+
+    def submit(self, fn, *args, **kwargs):
+        """Submits a callable to be executed with the given arguments.
+
+        Schedules the callable to be executed as fn(*args, **kwargs) and 
returns
+        a Future instance representing the execution of the callable.
+
+        Returns:
+            A Future representing the given call.
+        """
+        raise NotImplementedError()
+
+    def map(self, fn, *iterables, **kwargs):
+        """Returns an iterator equivalent to map(fn, iter).
+
+        Args:
+            fn: A callable that will take as many arguments as there are
+                passed iterables.
+            timeout: The maximum number of seconds to wait. If None, then there
+                is no limit on the wait time.
+
+        Returns:
+            An iterator equivalent to: map(func, *iterables) but the calls may
+            be evaluated out-of-order.
+
+        Raises:
+            TimeoutError: If the entire result iterator could not be generated
+                before the given timeout.
+            Exception: If fn(*args) raises for any values.
+        """
+        timeout = kwargs.get('timeout')
+        if timeout is not None:
+            end_time = timeout + time.time()
+
+        fs = [self.submit(fn, *args) for args in itertools.izip(*iterables)]
+
+        # Yield must be hidden in closure so that the futures are submitted
+        # before the first iterator value is required.
+        def result_iterator():
+            try:
+                # reverse to keep finishing order
+                fs.reverse()
+                while fs:
+                    # Careful not to keep a reference to the popped future
+                    if timeout is None:
+                        yield fs.pop().result()
+                    else:
+                        yield fs.pop().result(end_time - time.time())
+            finally:
+                for future in fs:
+                    future.cancel()
+        return result_iterator()
+
+    def shutdown(self, wait=True):
+        """Clean-up the resources associated with the Executor.
+
+        It is safe to call this method several times. Otherwise, no other
+        methods can be called after this one.
+
+        Args:
+            wait: If True then shutdown will not return until all running
+                futures have finished executing and the resources used by the
+                executor have been reclaimed.
+        """
+        pass
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        self.shutdown(wait=True)
+        return False
diff --git a/mercurial/thirdparty/concurrent/futures/__init__.py 
b/mercurial/thirdparty/concurrent/futures/__init__.py
new file mode 100644
--- /dev/null
+++ b/mercurial/thirdparty/concurrent/futures/__init__.py
@@ -0,0 +1,23 @@
+# Copyright 2009 Brian Quinlan. All Rights Reserved.
+# Licensed to PSF under a Contributor Agreement.
+
+"""Execute computations asynchronously using threads or processes."""
+
+__author__ = 'Brian Quinlan (br...@sweetapp.com)'
+
+from concurrent.futures._base import (FIRST_COMPLETED,
+                                      FIRST_EXCEPTION,
+                                      ALL_COMPLETED,
+                                      CancelledError,
+                                      TimeoutError,
+                                      Future,
+                                      Executor,
+                                      wait,
+                                      as_completed)
+from concurrent.futures.thread import ThreadPoolExecutor
+
+try:
+    from concurrent.futures.process import ProcessPoolExecutor
+except ImportError:
+    # some platforms don't have multiprocessing
+    pass
diff --git a/mercurial/thirdparty/concurrent/__init__.py 
b/mercurial/thirdparty/concurrent/__init__.py
new file mode 100644
--- /dev/null
+++ b/mercurial/thirdparty/concurrent/__init__.py
@@ -0,0 +1,3 @@
+from pkgutil import extend_path
+
+__path__ = extend_path(__path__, __name__)
diff --git a/mercurial/thirdparty/concurrent/LICENSE 
b/mercurial/thirdparty/concurrent/LICENSE
new file mode 100644
--- /dev/null
+++ b/mercurial/thirdparty/concurrent/LICENSE
@@ -0,0 +1,48 @@
+PYTHON SOFTWARE FOUNDATION LICENSE VERSION 2
+--------------------------------------------
+
+1. This LICENSE AGREEMENT is between the Python Software Foundation
+("PSF"), and the Individual or Organization ("Licensee") accessing and
+otherwise using this software ("Python") in source or binary form and
+its associated documentation.
+
+2. Subject to the terms and conditions of this License Agreement, PSF
+hereby grants Licensee a nonexclusive, royalty-free, world-wide
+license to reproduce, analyze, test, perform and/or display publicly,
+prepare derivative works, distribute, and otherwise use Python
+alone or in any derivative version, provided, however, that PSF's
+License Agreement and PSF's notice of copyright, i.e., "Copyright (c)
+2001, 2002, 2003, 2004, 2005, 2006 Python Software Foundation; All Rights
+Reserved" are retained in Python alone or in any derivative version 
+prepared by Licensee.
+
+3. In the event Licensee prepares a derivative work that is based on
+or incorporates Python or any part thereof, and wants to make
+the derivative work available to others as provided herein, then
+Licensee hereby agrees to include in any such work a brief summary of
+the changes made to Python.
+
+4. PSF is making Python available to Licensee on an "AS IS"
+basis.  PSF MAKES NO REPRESENTATIONS OR WARRANTIES, EXPRESS OR
+IMPLIED.  BY WAY OF EXAMPLE, BUT NOT LIMITATION, PSF MAKES NO AND
+DISCLAIMS ANY REPRESENTATION OR WARRANTY OF MERCHANTABILITY OR FITNESS
+FOR ANY PARTICULAR PURPOSE OR THAT THE USE OF PYTHON WILL NOT
+INFRINGE ANY THIRD PARTY RIGHTS.
+
+5. PSF SHALL NOT BE LIABLE TO LICENSEE OR ANY OTHER USERS OF PYTHON
+FOR ANY INCIDENTAL, SPECIAL, OR CONSEQUENTIAL DAMAGES OR LOSS AS
+A RESULT OF MODIFYING, DISTRIBUTING, OR OTHERWISE USING PYTHON,
+OR ANY DERIVATIVE THEREOF, EVEN IF ADVISED OF THE POSSIBILITY THEREOF.
+
+6. This License Agreement will automatically terminate upon a material
+breach of its terms and conditions.
+
+7. Nothing in this License Agreement shall be deemed to create any
+relationship of agency, partnership, or joint venture between PSF and
+Licensee.  This License Agreement does not grant permission to use PSF
+trademarks or trade name in a trademark sense to endorse or promote
+products or services of Licensee, or any third party.
+
+8. By copying, installing or otherwise using Python, Licensee
+agrees to be bound by the terms and conditions of this License
+Agreement.



To: indygreg, #hg-reviewers
Cc: mercurial-devel
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