1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
|
# Copyright 2009 Brian Quinlan. All Rights Reserved. See LICENSE file.
"""Implements ThreadPoolExecutor."""
__author__ = 'Brian Quinlan (brian@sweetapp.com)'
from futures._base import (PENDING, RUNNING, CANCELLED,
CANCELLED_AND_NOTIFIED, FINISHED,
ALL_COMPLETED,
LOGGER,
set_future_exception, set_future_result,
Executor, Future, FutureList, ThreadEventSink)
import atexit
import Queue
import threading
import weakref
# 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 function 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 they
# finish.
_thread_references = set() # Weakrefs to every active worker thread.
_shutdown = False # Indicates that the interpreter is shutting down.
def _python_exit():
global _shutdown
_shutdown = True
for thread_reference in _thread_references:
thread = thread_reference()
if thread is not None:
thread.join()
def _remove_dead_thread_references():
"""Remove inactive threads from _thread_references.
Should be called periodically to prevent thread objects from accumulating in
scenarios such as:
>>> while True:
>>> ... t = ThreadPoolExecutor(max_threads=5)
>>> ... t.map(int, ['1', '2', '3', '4', '5'])
"""
for thread_reference in set(_thread_references):
if thread_reference() is None:
_thread_references.discard(thread_reference)
atexit.register(_python_exit)
class _WorkItem(object):
def __init__(self, call, future, completion_tracker):
self.call = call
self.future = future
self.completion_tracker = completion_tracker
def run(self):
self.future._condition.acquire()
try:
if self.future._state == PENDING:
self.future._state = RUNNING
elif self.future._state == CANCELLED:
self.completion_tracker._condition.acquire()
try:
self.future._state = CANCELLED_AND_NOTIFIED
self.completion_tracker.add_cancelled()
return
finally:
self.completion_tracker._condition.release()
else:
LOGGER.critical('Future %s in unexpected state: %d',
id(self.future),
self.future._state)
return
finally:
self.future._condition.release()
try:
result = self.call()
except Exception, e:
set_future_exception(self.future, self.completion_tracker, e)
else:
set_future_result(self.future, self.completion_tracker, result)
def _worker(executor_reference, work_queue):
try:
while True:
try:
work_item = work_queue.get(block=True, timeout=0.1)
except Queue.Empty:
executor = executor_reference()
# Exit if:
# - The interpreter is shutting down.
# - The executor that owns the worker has been collected.
# - The executor that owns the worker has been shutdown.
if _shutdown or executor is None or executor._shutdown:
return
del executor
else:
work_item.run()
except Exception, e:
LOGGER.critical('Exception in worker', exc_info=True)
class ThreadPoolExecutor(Executor):
def __init__(self, max_threads):
"""Initializes a new ThreadPoolExecutor instance.
Args:
max_threads: The maximum number of threads that can be used to
execute the given calls.
"""
_remove_dead_thread_references()
self._max_threads = max_threads
self._work_queue = Queue.Queue()
self._threads = set()
self._shutdown = False
self._shutdown_lock = threading.Lock()
def _adjust_thread_count(self):
for _ in range(len(self._threads),
min(self._max_threads, self._work_queue.qsize())):
t = threading.Thread(target=_worker,
args=(weakref.ref(self), self._work_queue))
t.setDaemon(True)
t.start()
self._threads.add(t)
_thread_references.add(weakref.ref(t))
def run_to_futures(self, calls, timeout=None, return_when=ALL_COMPLETED):
self._shutdown_lock.acquire()
try:
if self._shutdown:
raise RuntimeError('cannot run new futures after shutdown')
futures = []
event_sink = ThreadEventSink()
for index, call in enumerate(calls):
f = Future(index)
w = _WorkItem(call, f, event_sink)
self._work_queue.put(w)
futures.append(f)
self._adjust_thread_count()
fl = FutureList(futures, event_sink)
fl.wait(timeout=timeout, return_when=return_when)
return fl
finally:
self._shutdown_lock.release()
run_to_futures.__doc__ = Executor.run_to_futures.__doc__
def shutdown(self):
self._shutdown_lock.acquire()
try:
self._shutdown = True
finally:
self._shutdown_lock.release()
shutdown.__doc__ = Executor.shutdown.__doc__
|
