Search code examples
cforkparent-childwaitpid

Example of waitpid() in use?

I know that waitpid() is used to wait for a process to finish, but how would one use it exactly?

Here what I want to do is, create two children and wait for the first child to finish, then kill the second child before exiting.

//Create two children
pid_t child1;
pid_t child2;
child1 = fork();

//wait for child1 to finish, then kill child2
waitpid() ... child1 {
kill(child2) }
Solution

  • Syntax of waitpid():

    pid_t waitpid(pid_t pid, int *status, int options);

    The value of pid can be:

    • < -1: Wait for any child process whose process group ID is equal to the absolute value of pid.
    • -1: Wait for any child process.
    • 0: Wait for any child process whose process group ID is equal to that of the calling process.
    • > 0: Wait for the child whose process ID is equal to the value of pid.

    The value of options is an OR of zero or more of the following constants:

    • WNOHANG: Return immediately if no child has exited.
    • WUNTRACED: Also return if a child has stopped. Status for traced children which have stopped is provided even if this option is not specified.
    • WCONTINUED: Also return if a stopped child has been resumed by delivery of SIGCONT.

    For more help, use man waitpid.