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python里多线程的写法
python里多线程的写法
今天用到python多线程的时候, 发现不知道如何正确的等待所有线程结束后再结束主线程.
其实到最后我才知道这都是杞人忧天, Thread()出来的实例本来就是等到主进程结束后才结束.
官方解释:
daemon A boolean value indicating whether this thread is a daemon thread (True) or not (False). This must be set before start() is called, otherwise RuntimeError is raised. Its initial value is inherited from the creating thread; the main thread is not a daemon thread and therefore all threads created in the main thread default to daemon = False.
The entire Python program exits when no alive non-daemon threads are left.
默认daemon是false, start之后也不会阻塞在那里(废话, 否则要多线程干嘛, 不过总会想到join会阻塞这点). 对于我的需要来说简直完美,其实什么都不用做嘛.
可以用setDaemon(True)改变daemon值. 这样的话, 就需要调用join等待子线程结束了. (好多此一举..)
for t in threads: t.join()
可以把所有要起的线程放到一个队列里面, 然后对每一个线程join. 这样的确是可以实现, 但看起来太丑, 用着实在别扭.
像如下这样, 其实for循环里面, 进程等待在第一个join那里:
#!/usr/bin/env python# -*- coding: utf-8 -*-from threading import Threadimport timedef target(i): time.sleep(10-i)def main(): threads = [] for i in range(10): t = Thread(target=target,args=(i,)) threads.append(t) for t in threads: t.start() for idx,t in enumerate(threads): print idx t.join()if __name__ == ‘__main__‘: main()multiprocessing.Pool
又用Queue实现了一下, 但还是太丑陋, 封装不好. 然后才搜索到Python其实有个multiprocessing.Pool, 可以很好看的实现这个功能:
#!/usr/bin/env python# -*- coding: utf-8 -*-from multiprocessing import Poolimport timedef work(): print time.time() time.sleep(4)def main(): pool = Pool(processes=4) for i in range(4): pool.apply_async(work) pool.close() pool.join()if __name__ == ‘__main__‘: main()借鉴官方的Pool, 尝试自己实现一下最简单的Multiprocessing Pool
#!/usr/bin/env python# -*- coding: utf-8 -*-from threading import Threadfrom Queue import Queueimport timedef hello(msg=None): print time.time(),msg time.sleep(5)class MPool(object): def posttask(self,func): def inner(*args, **kwargs): q = args[0] real_args = args[1:] func(*real_args, **kwargs) q.task_done() return inner def __init__(self): self._queue = Queue() #简单起见没有设置队列上限 def run_task(self, target, *args, **kwargs): task = Thread(target=self.posttask(target), args=(self._queue,)+args, kwargs=kwargs) self._queue.put(task) task.setDaemon(True) task.start() def join(self): self._queue.join()def main(): p = MPool() for i in range(10): p.run_task(hello,i) p.join()if __name__ == ‘__main__‘: main()最后再提一下, 我的初衷只是想等所有线程结束后再退出. 默认就是这样的, join什么的都不用.
python里多线程的写法