C - WEXITSTATUS() question

Applications Programming
1

I want to check if an application is still running under C. So far I've been using

int rc;
rc=WEXITSTATUS( [PID here] )

if(rc > 0)
{
   //then I exited
}

I was wondering seeing as WEXITSTATUS in man pages is close to the WAIT() if it was thread blocking and if it was how would I go about making my code non-blocking without threads?

2 
pid_t waitpid(pid_t pid, int *status, int options);
// use WNOHANG as the option

This returns the pid when if the process ended, or it checks and returns right away if the child process is still active.

---------- Post updated at 11:48 ---------- Previous update was at 11:00 ----------

If it is not a child process -

try

errno=0;
if(kill(pid, 0) == 0 )
{
    printf("process running\n");
}
else

{
    if(errno==ESRCH)
        printf("process stopped\n");
    else
    {
        perror("cannot signal the process");
        exit(1);
     }
}
3

The thing is I'm creating a daemon to check that certain applications are running(via PID) I do not initially launch them(so they are not my children) and I don't really feel like trying to kill something that I'm to prevent from stopping. would waitpid still work even though it's not my child?

4

if your just checking to see if PID exists. use kill(pid,0); see man page for details.

5

When you're writing a daemon consider using a lockfile to prevent two instacnes of the daemon from running. Otherwise the kill(pid,0) approach works fine.