我有一个GUI应用程序,需要从网络中获取和解析各种资源,除了GUI主循环。
我搜索了使用Python多进程模块的选项,因为这些获取操作不仅包含阻塞IO,还包括重量级解析,所以在这里使用多进程可能是更好的选择,而不是Python线程。
使用Twisted会很容易,但这次Twisted不是一个选项。
我在这里找到了一个简单的解决方案:
Python subprocess: callback when cmd exits
问题是回调神奇地没有在MainThread内被调用。
所以我想出了以下解决方案:
delegate.py
import os
import multiprocessing as mp
import signal
from collections import namedtuple
import uuid
import logging
_CALLBACKS = {}
_QUEUE = mp.Queue()
info = logging.getLogger(__name__).info
class Call(namedtuple('Call', 'id finished result error')):
def attach(self, func):
if not self.finished:
_CALLBACKS.setdefault(self.id, []).append(func)
else:
func(self.result or self.error)
return self
def callback(self):
assert self.finished, 'Call not finished yet'
r = self.result or self.error
for func in _CALLBACKS.pop(self.id, []):
func(r)
def done(self, result=None, error=None):
assert not self.finished, 'Call already finished'
return self._replace(finished=(-1 if error else 1),
result=result, error=error)
@classmethod
def create(clss):
call = clss(uuid.uuid4().hex, 0, None, None) # uuid ???
return call
def run(q, cb, func, args=None, kwargs=None):
info('run: try running %s' % func)
try:
cb = cb.done(result=func(*(args or ()), **(kwargs or {})))
except Exception, err:
cb = cb.done(error=err)
q.put(cb)
os.kill(os.getppid(), signal.SIGUSR2) # SIGUSR2 ???
info('run: leaving')
def on_callback(sig, frame):
info('on_callback: checking queue ...')
c = _QUEUE.get(True, 2)
info('on_callback: got call - %s' % repr(c))
c.callback()
signal.signal(signal.SIGUSR2, on_callback) # SIGUSR2 ???
def delegate(func, *args, **kwargs):
info('delegate: %s %s' % (func, args,))
cb = Call.create()
mp.Process(target=run, args=(_QUEUE, cb, func, args, kwargs,)).start()
return cb
__all__ = ['delegate']
使用
from delegate import delegate
def sleeper(secs):
assert secs >= 1, 'I need my Augenpflege'
info('sleeper: will go to sleep for %s secs' % secs)
sleep(secs)
info('sleeper: woke up - returning result')
return ['sleeper', 'result']
def on_sleeper_result(r):
if isinstance(r, Exception):
info('on_sleeper_result: got error: %s' % r)
else:
info('on_sleeper_result: got result: %s' % r)
from delegate import delegate
delegate(sleeper, 3).attach(on_sleeper_result)
delegate(sleeper, -3).attach(on_sleeper_result)
while 1:
info('main: loop')
sleep(1)
输出
0122 08432 MainThread INFO delegate: <function sleeper at 0x163e320> (3,)
0123 08432 MainThread INFO delegate: <function sleeper at 0x163e320> (-3,)
0124 08437 MainThread INFO run: try running <function sleeper at 0x163e320>
0124 08437 MainThread INFO sleeper: will go to sleep for 3 secs
0124 08432 MainThread INFO main: loop
0125 08438 MainThread INFO run: try running <function sleeper at 0x163e320>
0126 08438 MainThread INFO run: leaving
0126 08432 MainThread INFO on_callback: checking queue ...
0126 08432 MainThread INFO on_callback: got call - Call(id='057649cba7d840e3825aa5ac73248f78', finished=-1, result=None, error=AssertionError('I need my Augenpflege',))
0127 08432 MainThread INFO on_sleeper_result: got error: I need my Augenpflege
0127 08432 MainThread INFO main: loop
1128 08432 MainThread INFO main: loop
2129 08432 MainThread INFO main: loop
3127 08437 MainThread INFO sleeper: woke up - returning result
3128 08437 MainThread INFO run: leaving
3128 08432 MainThread INFO on_callback: checking queue ...
3129 08432 MainThread INFO on_callback: got call - Call(id='041420c6c83a489aa5c7409c662d4917', finished=1, result=['sleeper', 'result'], error=None)
3129 08432 MainThread INFO on_sleeper_result: got result: ['sleeper', 'result']
3129 08432 MainThread INFO main: loop
4130 08432 MainThread INFO main: loop
5132 08432 MainThread INFO main: loop
...
到目前为止,这个方案运行得相当不错,但是我对多进程模块的经验有限,我有些不确定它是否会带来影响。我的问题是,在使用多进程时,我应该特别注意哪些事项...或者说,使用Python标准库进行异步回调机制的'更正确'的模式是什么?