python之os.waitpid()

python中os.waitpid() 注意：windows操作系统中os模块中没有os.fork() 函数

一下代码为os.waitpid()用法的演示。

该程序的3个示范输出再次证明了一部并发进程不可预测的本质

import os
import sys
import time

try :
    forkPID1 = os.fork()
except OSError :  # 如果操作系统不能创建进程，osfork()将会发出一个OSError异常
    sys.exit('Unable to create first child.')

if forkPID1 != 0 :
    try :
        forkPID2 = os.fork()
    except OSError :
        sys.exit('Unable to create first child.')

    if forkPID2 > 0 :
        print 'Parent waiting for child precesses ...\n' + \
            '\t tpid : %d , forkPID1 : %d , forkPID2 : %d' \
            % ( os.getpid() , forkPID1 , forkPID2)

        try :
            child2 = os.waitpid (forkPID2 , 0)[0]
        except OSError :
            sys.exit("No child process with pid %d." %(forkPID2) )

        print 'Parent Child %d finished.' % child2

    elif forkPID2 == 0 :
        print 'Chile2 sleeping fot 4 seconds ....\n' + \
            '\tpid : %d , forkPID1: %d , forkPID2: %d' \
            % (os.getpid() , forkPID1 , forkPID2 )
        time.sleep(4)  #规定进程保持的休眠时间 ， 以秒为单位

elif forkPID1 == 0 :
    print 'Child1 sleeping for 2 seconds ....\n' + \
        '\tpid : %d , forkPID1: %d' \
        % (os.getpid() , forkPID1)
    time.sleep(2)

3个示范输出：
Parent waiting for child precesses ...
     tpid : 2468 , forkPID1 : 2469 , forkPID2 : 2470
Child1 sleeping for 2 seconds ....
    pid : 2469 , forkPID1: 0
Chile2 sleeping fot 4 seconds ....
    pid : 2470 , forkPID1: 2469 , forkPID2: 0
Parent Child 2470 finished.

Parent waiting for child precesses ...
     tpid : 2465 , forkPID1 : 2466 , forkPID2 : 2467
Child1 sleeping for 2 seconds ....
Chile2 sleeping fot 4 seconds ....
    pid : 2466 , forkPID1: 0
    pid : 2467 , forkPID1: 2466 , forkPID2: 0
Parent Child 2467 finished.

Parent waiting for child precesses ...
     tpid : 2634 , forkPID1 : 2635 , forkPID2 : 2636
Child1 sleeping for 2 seconds ....
    pid : 2635 , forkPID1: 0
Chile2 sleeping fot 4 seconds ....
    pid : 2636 , forkPID1: 2635 , forkPID2: 0
Parent Child 2636 finished.