Subprocess analysis generated by the fork () function in python

In the python OS module, the fork () function is used to generate sub-processes. The generated sub-processes are the mirror of the parent process, but they have their own address space, the sub-process replicates the parent process memory to itself. The execution between the two processes is independent of each other, and the execution sequence can be uncertain, random, and unpredictable, this is similar to the execution sequence of multiple threads. Import OS def child (): print 'a new child: ', OS. getpid () print 'parent id is: ', OS. getppid () OS. _ exit (0) def parent (): while True: newpid = OS. fork () print newpid if newpid = 0: child () else: pids = (OS. getpid (), newpid) print "parent: % d, child: % d" % pids print "parent:", OS. getppid () if raw_input () = 'q': break parent () after we load the OS module, the fork () function in our parent function generates a sub-process, the return value newpid has two values. One value is 0, which indicates the sub-process. The other value is an integer greater than 0, which is used for the table. Shows the parent process. This constant is the pid of the child process. We can clearly see two return values through the print statement. If fork () returns a negative value, it indicates that the sub-process is not successfully generated (this is not considered in this simple program ). If newpid = 0, it indicates that we enter the child process, that is, the child () function. In the child process, we output our own id and the parent process id. If the else statement is entered, it indicates that newpid> 0, we enter the parent process, in the parent process OS. getpid () gets its own id. fork () returns newpid, which indicates the id of the child process. At the same time, we output the id of the parent process. through the experiment, we can see that the execution sequence of if and else statements is uncertain. The execution sequence of sub-and parent processes is determined by the scheduling algorithm of the operating system.