Python多进程机制实例详解

本文实例讲述了Python多进程机制。分享给大家供大家参考。具体如下：

在以前只是接触过PYTHON的多线程机制，今天搜了一下多进程，相关文章好像不是特别多。看了几篇，小试了一把。程序如下，主要内容就是通过PRODUCER读一个本地文件，一行一行的放到队列中去。然后会有相应的WORKER从队列中取出这些行。

    import multiprocessing
    import os
    import sys
    import Queue
    import time
    def writeQ(q,obj):
        q.put(obj,True,None)
        print "put size: ",q.qsize()
    def readQ(q):
        ret = q.get(True,1)
        print "get size: ",q.qsize()
        return ret
    def producer(q):
        time.sleep(5)  #让进行休息几秒 方便ps命令看到相关内容
        pid = os.getpid()
        handle_file = '/home/dwapp/joe.wangh/test/multiprocess/datafile'
        with open(handle_file,'r') as f:   #with...as... 这个用法今天也是第一次看到的
            for line in f:
                print "producer <" ,pid , "> is doing: ",line
                writeQ(q,line.strip())
        q.close()
    def worker(q):
        time.sleep(5)  #让进行休息几秒 方便ps命令看到相关内容
        pid = os.getpid()
        empty_count = 0
        while True:
            try:
                task = readQ(q)
                print "worker <" , pid , "> is doing: " ,task
                '''
                如果这里不休眠的话 一般情况下所有行都会被同一个子进程读取到 为了使实验效果更加清楚 在这里让每个进程读取完
    一行内容时候休眠5s 这样就可以让其他的进程到队列中进行读取
                '''
                time.sleep(5)  
            except Queue.Empty:
                empty_count += 1
                if empty_count == 3:
                    print "queue is empty, quit"
                    q.close()
                    sys.exit(0)
    def main():
        concurrence = 3
        q = multiprocessing.Queue(10)
        funcs = [producer , worker]
        for i in range(concurrence-1):
            funcs.append(worker)
        for item in funcs:
            print str(item)
        nfuncs = range( len(funcs) )
        processes = []    
        for i in nfuncs:
            p = multiprocessing.Process(target=funcs[i] , args=(q,))
            processes.append(p)
        print "concurrence worker is : ",concurrence," working start"
        for i in nfuncs:
            processes[i].start()
        for i in nfuncs:
            processes[i].join()
        print "all DONE"
    if __name__ == '__main__':
        main()

实验结果如下：

    dwapp@pttest1:/home/dwapp/joe.wangh/test/multiprocess>python 1.py 
    <function producer at 0xb7b9141c>
    <function worker at 0xb7b91454>
    <function worker at 0xb7b91454>
    <function worker at 0xb7b91454>
    concurrence worker is : 3 working start
    producer < 28320 > is doing: line 1
    put size: 1
    producer < 28320 > is doing: line 2
    put size: 2
    producer < 28320 > is doing: line 3
    put size: 3
    producer < 28320 > is doing: line 4
    put size: 3
    producer < 28320 > is doing: line 5
    get size: 3
    put size: 4
    worker < 28321 > is doing: line 1
    get size: 3
    worker < 28322 > is doing: line 2
    get size: 2
    worker < 28323 > is doing: line 3
    get size: 1
    worker < 28321 > is doing: line 4
    get size: 0
    worker < 28322 > is doing: line 5
    queue is empty, quit
    queue is empty, quit
    queue is empty, quit
    all DONE

程序运行期间在另外一个窗口进行ps命令 可以观测到一些进程的信息

    dwapp@pttest1:/home/dwapp/joe.wangh/test/multiprocess>ps -ef | grep python
    dwapp  13735 11830 0 Nov20 pts/12  00:00:05 python
    dwapp  28319 27481 8 14:04 pts/0  00:00:00 python 1.py
    dwapp  28320 28319 0 14:04 pts/0  00:00:00 python 1.py
    dwapp  28321 28319 0 14:04 pts/0  00:00:00 python 1.py
    dwapp  28322 28319 0 14:04 pts/0  00:00:00 python 1.py
    dwapp  28323 28319 0 14:04 pts/0  00:00:00 python 1.py
    dwapp  28325 27849 0 14:04 pts/13  00:00:00 grep python
    dwapp@pttest1:/home/dwapp/joe.wangh/test/multiprocess>ps -ef | grep python
    dwapp  13735 11830 0 Nov20 pts/12  00:00:05 python     #此时28320进程 也就是PRODUCER进程已经结束
    dwapp  28319 27481 1 14:04 pts/0  00:00:00 python 1.py
    dwapp  28321 28319 0 14:04 pts/0  00:00:00 python 1.py
    dwapp  28322 28319 0 14:04 pts/0  00:00:00 python 1.py
    dwapp  28323 28319 0 14:04 pts/0  00:00:00 python 1.py
    dwapp  28328 27849 0 14:04 pts/13  00:00:00 grep python
    dwapp@pttest1:/home/dwapp/joe.wangh/test/multiprocess>ps -ef | grep python
    dwapp  13735 11830 0 Nov20 pts/12  00:00:05 python
    dwapp  28319 27481 0 14:04 pts/0  00:00:00 python 1.py
    dwapp  28321 28319 0 14:04 pts/0  00:00:00 python 1.py
    dwapp  28322 28319 0 14:04 pts/0  00:00:00 python 1.py
    dwapp  28323 28319 0 14:04 pts/0  00:00:00 [python] <defunct>  #这里应该是代表28323进程（WORKER）已经运行结束了
    dwapp  28331 27849 0 14:04 pts/13  00:00:00 grep python
    dwapp@pttest1:/home/dwapp/joe.wangh/test/multiprocess>ps -ef | grep python
    dwapp  13735 11830 0 Nov20 pts/12  00:00:05 python
    dwapp  28337 27849 0 14:05 pts/13  00:00:00 grep python

希望本文所述对大家的Python程序设计有所帮助。