以python代码解释fork系统调用

import os

print('Process (%s) start...' % os.getpid())
# Only works on Unix/Linux/Mac:
pid = os.fork()
print ("haha")
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))


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

执行到os.fork()时，发起fork系统调用，操作系统复制父进程得到子进程。fork系统调用完毕，返回给父进程子进程的id号，返回给子进程0，然后父子进城开始执行。我们可以看到haha被打印了两次，更加说明了子进程是复制父进程得来的