匿名管道

管道是一個單向通道,有點類似共享內存緩存.管道有兩端,包括輸入端和輸出端.對于一個進程的而言,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:
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:
代碼如下:
('hello from parent', 5053, 5054)
('hello from child', 5054)
how are you

how are you

how are you

how are you

我們也可以改進代碼,不用os.read()從管道中讀取二進制字節,而是從文件對象中讀取字符串.這時需要用到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.還有一點要改進的地方是,把父進程和子進程的管道中不用的一端關閉掉.
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)