创建一个进程的 C 程序，该进程被阻塞直到终止

Question

How do I create a process in C and play with it's state?

• I would like to know how to create a process.
• I would like to know how to put this process in Blocked state.
• I would like to know how to put this process in a Zombie state.

A guide on how to work with processes on C would be helpfull I just can't find it around. This way I could answer those questions myself.

I've been playing around with ps to see the state of a process but dont really know how to start.

Am working on Linux, sorry for my English.

Answer 1

Create a child process using fork() - your program itself runs in a process anyway

Put process in "blocked" state:- use sleep() or issue a blocking write() - read manpages for more info - dunno what exactly you mean by 'blocked' here

Creating a zombie - fork() and then exit the program. You can "see" the zombie from ps

Answer 2

if you throw out your understanding of typical parent child processes, it becomes simple

childpid=fork();
switch (childpid){
case 0 : //normally considered the child, but we will use it to continue on
     finish_program();
     return(0);
case -1 : //error occurred
default : //normally considered the parent, but our "blocked" process
     wait(childpid); //waits for the child process to terminate
     dostuff();
}

the parent is blocked until the child terminates

normally you would use semaphores and shared memory to block a process, but this is a good start

Answer 3

@user1869399 - I think you asked a very good question, and I think Bug Catcher gave a very good answer.

Key to Bug Catcher's suggestion about creating a "zombie" is forking a process without "cleaning up" after it exits (ie failing to call "waitpid()").

Here is a very good link on Linux process states:

• http://www.tldp.org/LDP/tlk/kernel/processes.html

Also, look at the "notes" section in the "man page" for waitpid():

• http://www.kernel.org/doc/man-pages/online/pages/man2/wait.2.html