Python 多进程锁multiprocess Lock

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Lock

当多个进程需要访问共享资源的时候，Lock可以用来避免访问的冲突。

import multiprocessingimport sysdef worker_with(lock, f):    with lock:        fs = open(f,"a+")        fs.write('Lock acquired via with\n')        fs.close()        def worker_no_with(lock, f):    lock.acquire()    try:        fs = open(f,"a+")        fs.write('Lock acquired directly\n')        fs.close()    finally:        lock.release()if __name__ == "__main__":    f = "file.txt"      lock = multiprocessing.Lock()    w = multiprocessing.Process(target=worker_with, args=(lock, f))    nw = multiprocessing.Process(target=worker_no_with, args=(lock, f))    w.start()    nw.start()    w.join()    nw.join()

在上面的例子中，如果两个进程没有使用lock来同步,则他们对同一个文件的写操作可能会出现混乱。

Semaphore

Semaphore用来控制对共享资源的访问数量，例如池的最大连接数。

import multiprocessingimport time def worker(s,i):    s.acquire()    print(multiprocessing.current_process().name + " acquire")    time.sleep(i)    print(multiprocessing.current_process().name + " release")    s.release()if __name__ == "__main__":      s = multiprocessing.Semaphore(2)    for i in range(5):        p = multiprocessing.Process(target=worker, args=(s,i*2))        p.start()

上面的实例中使用semaphore限制了最多有2个进程同时执行。

Event

Event用来实现进程间同步通信。

import multiprocessingimport timedef wait_for_event(e):    """Wait for the event to be set before doing anything"""    print ('wait_for_event: starting')    e.wait()    print ('wait_for_event: e.is_set()->' + str(e.is_set()))def wait_for_event_timeout(e, t):    """Wait t seconds and then timeout"""    print ('wait_for_event_timeout: starting')    e.wait(t)    print ('wait_for_event_timeout: e.is_set()->' + str(e.is_set()))if __name__ == '__main__':    e = multiprocessing.Event()    w1 = multiprocessing.Process(name='block',                                  target=wait_for_event,                                 args=(e,))    w1.start()    w2 = multiprocessing.Process(name='non-block',                                  target=wait_for_event_timeout,                                  args=(e, 2))    w2.start()    time.sleep(3)    e.set()    print ('main: event is set')

#the output is:
#wait_for_event_timeout: starting
#wait_for_event: starting
#wait_for_event_timeout: e.is_set()->False
#main: event is set
#wait_for_event: e.is_set()->True

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