Python学习系列 - 进程和线程（九）

我们的电脑总是可以打开很多的程序，而且相同的程序会同时实现多个功能。这就是多进程和多线程！

多进程

multiprocessing

Unix/Linux操作系统提供了一个fork()系统调用，可是Windows上面无法调用。
由于Python是跨平台的，自然也应该提供一个跨平台的多进程支持。multiprocessing模块就是跨平台版本的多进程模块。

from multiprocessing import Process
import os


# 子进程要执行的代码
def run_proc(name):
    print('Run child process %s (%s)...' % (name, os.getpid()))


if __name__ == '__main__':
    print('Parent process %s.' % os.getpid())
    p = Process(target=run_proc, args=('test',))
    print('Child process will start.')
    p.start()
    p.join()
    print('Child process end.')
运行结果：
Parent process 12588.
Child process will start.
Run child process test (11108)...
Child process end.

Pool

如果要启动大量的子进程，可以用进程池的方式批量创建子进程：

from multiprocessing import Pool
import os, time, random

def long_time_task(name):
    print('Run task %s (%s)...' % (name, os.getpid()))
    start = time.time()
    time.sleep(random.random() * 3)
    end = time.time()
    print('Task %s runs %0.2f seconds.' % (name, (end - start)))

if __name__=='__main__':
    print('Parent process %s.' % os.getpid())
    p = Pool(4)
    for i in range(5):
        p.apply_async(long_time_task, args=(i,))
    print('Waiting for all subprocesses done...')
    p.close()
    p.join()
    print('All subprocesses done.')
运行结果：
Parent process 16320.
Waiting for all subprocesses done...
Run task 0 (3480)...
Run task 1 (7388)...
Run task 2 (14396)...
Run task 3 (14288)...
Task 2 runs 0.43 seconds.
Run task 4 (14396)...
Task 0 runs 0.44 seconds.
Task 4 runs 0.49 seconds.
Task 1 runs 1.58 seconds.
Task 3 runs 2.92 seconds.
All subprocesses done.

多线程

启动一个线程就是把一个函数传入并创建Thread实例，然后调用start()开始执行：

# 新线程执行的代码:
def loop():
    print('thread %s is running...' % threading.current_thread().name)
    n = 0
    while n < 5:
        n = n + 1
        print('thread %s >>> %s' % (threading.current_thread().name, n))
        time.sleep(1)
    print('thread %s ended.' % threading.current_thread().name)


print('thread %s is running...' % threading.current_thread().name)
t = threading.Thread(target=loop, name='LoopThread')
t.start()
t.join()
print('thread %s ended.' % threading.current_thread().name)
运行结果：
thread MainThread is running...
thread LoopThread is running...
thread LoopThread >>> 1
thread LoopThread >>> 2
thread LoopThread >>> 3
thread LoopThread >>> 4
thread LoopThread >>> 5
thread LoopThread ended.
thread MainThread ended.