【python】多进程锁multiprocess.Lock
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同步的方法基本与多线程相同。
1) 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 multiprocessing
- import sys
- def 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。
2)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 multiprocessing
- import 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。
3)Event
Event用来实现进程间同步通信。
- import multiprocessing
- import time
- def 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