Which child process send SIGCHLD

Question

I'm trying to understand the signal handling and process. I have a parent process that created several child processes. Now in the parent process I have a list of all child processes. when a child is terminated I want to delete it from the list. I know that when a child is terminated he's sending SIGCHLD to the parent. OK, now it's the tricky part, how can I find out if that child terminated or just suspended or something else?

Answer 1

Using the options argument of the wait() family of functions (waitpid(),waitid()).

http://linux.die.net/man/2/waitid

Answer 2

As you said

when a child is terminated he's sending SIGCHLD to the parent

Make the parent call wait().

Either

• by a blocking call to wait() or
• on a continous base or
• by seting up a signal handler serving SIGCHLD which in turn calls wait().

If having called waitpid() with a pid of -1 using the option WUNTRACED and then applying the macro WIFSTOPPED to the value returend by waitpid() it tells you whether the process was stopped or ended.

For Linux since kernel version 2.6.10 the same as for WIFSTOPPED applies to WCONTINUED.

Answer 3

There is a system call in signal.h - sigaction() , similar to siganl( ) but more useful.
Visit http://man7.org/linux/man-pages/man2/sigaction.2.html

The signal handler function prototype for sigaction() looks like this:

void sa_handler(int signo, siginfo_t *si, void *ucontext);

It has an argument of type siginfo_t which contains all the information about the signal including the pid of the process which sent it.
Though using conventional signal handling mechanism, it can be done using waitid() as mentioned in previous answer(s) but waitid() needs pid as one of its argument.