Python多进程

import os

print('Process (%s) start...' % os.getpid())
# Only works on Unix/Linux/Mac:
pid = os.fork()
if pid == 0:
    print('I am child process (%s) and my parent is %s.' % (os.getpid(), os.getppid()))
else:
    print('I (%s) just created a child process (%s).' % (os.getpid(), pid))

Process (876) start...
I (876) just created a child process (877).
I am child process (877) and my parent is 876.

from multiprocessing import Process
import os
#子进程执行的代码
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',)) #创建子进程Process实例
    print('Child process will start.')
    p.start() #start()方法启动
    p.join() #等待子进程结束后继续往下进行 通常用于进程间的同步
    print('Child process end.')

Parent process 928.
Child process will start.
Run child process test (929)...
Child process end.

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)
    # Pool的默认大小为为CPU的核数
    for i in range(5):
        p.apply_async(long_time_task, args=(i,))
    print('Waiting for all subprocesses done...')
    p.close()
    p.join() 
    # join()会等待所有子进程执行完毕 调用join()前必须执行close()
    # 调用close()后就不能添加新的Process
　　 
    print('All subprocesses done.')

Parent process 1784.
Waiting for all subprocesses done...
Run task 0 (8128)...
Run task 1 (9688)...
Run task 2 (7180)...
Run task 3 (6308)...
Task 2 runs 0.23 seconds.
Run task 4 (7180)...
Task 3 runs 0.62 seconds.
Task 1 runs 1.44 seconds.
Task 0 runs 2.14 seconds.
Task 4 runs 2.32 seconds.
All subprocesses done.

from multiprocessing import Process, Queue
import os, time, random

# 写数据进程执行的代码:
def write(q):
    print('Process to write: %s' % os.getpid())
    for value in ['A', 'B', 'C']:
        print('Put %s to queue...' % value)
        q.put(value)
        time.sleep(random.random())

# 读数据进程执行的代码:
def read(q):
    print('Process to read: %s' % os.getpid())
    while True:
        value = q.get(True)
        print('Get %s from queue.' % value)

if __name__=='__main__':
    # 父进程创建Queue，并传给各个子进程：
    q = Queue()
    pw = Process(target=write, args=(q,))
    pr = Process(target=read, args=(q,))
    # 启动子进程pw，写入:
    pw.start()
    # 启动子进程pr，读取:
    pr.start()
    # 等待pw结束:
    pw.join()
    # pr进程里是死循环，无法等待其结束，只能强行终止:
    pr.terminate()

Process to write: 50563
Put A to queue...
Process to read: 50564
Get A from queue.
Put B to queue...
Get B from queue.
Put C to queue...
Get C from queue.