Python多进程同步Lock、Semaphore、Event的使用

"""Python多进程同步Lock、Semaphore、Event实例,Lock用来避免访问冲突、Semaphore用来控制对共享资源的访问数量、Event用来实现进程间同步通信,"""
# 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 time
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()


def 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()



# Semaphore用来控制对共享资源的访问数量，例如池的最大连接数
def worker(s, i):
    s.acquire()
    print(multiprocessing.current_process().name + "acquire")
    time.sleep(i)
    print(multiprocessing.current_process().name + "release")
    s.release()

def main1():
    # 使用sempaphore限制了最多有2个进程同时执行
    s = multiprocessing.Semaphore(2)
    for i in range(5):
        p = multiprocessing.Process(target=worker, args=(s, i*2))
        p.start()


# Event用来实现进程间同步通信
def wait_for_event(e):
    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):
    print('wait_for_event_timeout: starting')
    e.wait(t)
    print('wait_for_event_timeout: e.is_set()->' + str(e.is_set()))

def main2():
    e = multiprocessing.Event()
    w1 = multiprocessing.Process(target=wait_for_event, args=(e,))
    w1.start()
    w2 = multiprocessing.Process(target=wait_for_event_timeout, args=(e, 2))
    w2.start()
    time.sleep(3)
    e.set()
    print("main: event is set")