Python進(jìn)程通信之匿名管道實(shí)例講解

更新時(shí)間：2015年04月11日 11:38:42 投稿：junjie

這篇文章主要介紹了Python進(jìn)程通信之匿名管道實(shí)例講解,本文直接給出代碼實(shí)例,代碼中包含詳細(xì)注釋,需要的朋友可以參考下

匿名管道

管道是一個單向通道,有點(diǎn)類似共享內(nèi)存緩存.管道有兩端,包括輸入端和輸出端.對于一個進(jìn)程的而言,它只能看到管道一端,即要么是輸入端要么是輸出端.

os.pipe()返回2個文件描述符(r, w),表示可讀的和可寫的.示例代碼如下:

#!/usr/bin/python
import time
import os

def child(wpipe):
    print('hello from child', os.getpid())
    while True:
        msg = 'how are you\n'.encode()
        os.write(wpipe, msg)
        time.sleep(1)

def parent():
    rpipe, wpipe = os.pipe()
    pid = os.fork()
    if pid == 0:
        child(wpipe)
        assert False, 'fork child process error!'
    else:
        os.close(wpipe)
        print('hello from parent', os.getpid(), pid)
        fobj = os.fdopen(rpipe, 'r')
        while True:
            recv = os.read(rpipe, 32)
            print recv

parent()

輸出如下:

復(fù)制代碼代碼如下:

('hello from parent', 5053, 5054)
('hello from child', 5054)
how are you

how are you

我們也可以改進(jìn)代碼,不用os.read()從管道中讀取二進(jìn)制字節(jié),而是從文件對象中讀取字符串.這時(shí)需要用到os.fdopen()把底層的文件描述符(管道)包裝成文件對象,然后再用文件對象中的readline()方法讀取.這里請注意文件對象的readline()方法總是讀取有換行符'\n'的一行,而且連換行符也讀取出來.還有一點(diǎn)要改進(jìn)的地方是,把父進(jìn)程和子進(jìn)程的管道中不用的一端關(guān)閉掉.

復(fù)制代碼代碼如下:

#!/usr/bin/python
import time
import os

def child(wpipe):
    print('hello from child', os.getpid())
    while True:
        msg = 'how are you\n'.encode()
        os.write(wpipe, msg)
        time.sleep(1)

def parent():
    rpipe, wpipe = os.pipe()
    pid = os.fork()
    if pid == 0:
        os.close(rpipe)
        child(wpipe)
        assert False, 'fork child process error!'
    else:
        os.close(wpipe)
        print('hello from parent', os.getpid(), pid)
        fobj = os.fdopen(rpipe, 'r')
        while True:
            recv = fobj.readline()[:-1]
            print recv

parent()

輸出如下:

復(fù)制代碼代碼如下:

('hello from parent', 5108, 5109)

('hello from child', 5109)

how are you

how are you

how are you

如果要與子進(jìn)程進(jìn)行雙向通信,只有一個pipe管道是不夠的,需要2個pipe管道才行.以下示例在父進(jìn)程新建了2個管道,然后再fork子進(jìn)程.os.dup2()實(shí)現(xiàn)輸出和輸入的重定向.spawn功能類似于subprocess.Popen(),既能發(fā)送消息給子進(jìn)程,由能從子子進(jìn)程獲取返回?cái)?shù)據(jù).

復(fù)制代碼代碼如下:

#!/usr/bin/python
#coding=utf-8
import os, sys

def spawn(prog, *args):
stdinFd = sys.stdin.fileno()
stdoutFd = sys.stdout.fileno()

parentStdin, childStdout = os.pipe()
childStdin, parentStdout= os.pipe()

    pid = os.fork()
    if pid:
        os.close(childStdin)
        os.close(childStdout)
        os.dup2(parentStdin, stdinFd)#輸入流綁定到管道,將輸入重定向到管道一端parentStdin
        os.dup2(parentStdout, stdoutFd)#輸出流綁定到管道,發(fā)送到子進(jìn)程childStdin
    else:
        os.close(parentStdin)
        os.close(parentStdout)
        os.dup2(childStdin, stdinFd)#輸入流綁定到管道
        os.dup2(childStdout, stdoutFd)
        args = (prog, ) + args
        os.execvp(prog, args)
        assert False, 'execvp failed!'

if __name__ == '__main__':
mypid = os.getpid()
spawn('python', 'pipetest.py', 'spam')

    print 'Hello 1 from parent', mypid #打印到輸出流parentStdout, 經(jīng)管道發(fā)送到子進(jìn)程childStdin
    sys.stdout.flush()
    reply = raw_input()
    sys.stderr.write('Parent got: "%s"\n' % reply)#stderr沒有綁定到管道上

    print 'Hello 2 from parent', mypid
    sys.stdout.flush()
    reply = sys.stdin.readline()#另外一種方式獲得子進(jìn)程返回信息
    sys.stderr.write('Parent got: "%s"\n' % reply[:-1])

pipetest.py代碼如下:

復(fù)制代碼代碼如下:

#coding=utf-8
import os, time, sys

mypid = os.getpid()
parentpid = os.getppid()
sys.stderr.write('child %d of %d got arg: "%s"\n' %(mypid, parentpid, sys.argv[1]))

for i in range(2):
    time.sleep(3)
    recv = raw_input()#從管道獲取數(shù)據(jù),來源于父經(jīng)常stdout
    time.sleep(3)
    send = 'Child %d got: [%s]' % (mypid, recv)
    print(send)#stdout綁定到管道上,發(fā)送到父進(jìn)程stdin
    sys.stdout.flush()

輸出:

復(fù)制代碼代碼如下:

child 7265 of 7264 got arg: "spam"

Parent got: "Child 7265 got: [Hello 1 from parent 7264]"

Parent got: "Child 7265 got: [Hello 2 from parent 7264]"

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