Steps:
Fork and start process in a different program group
Stop process with SIGTSTP
Restart process with SIGCONT
Process ends
Problem: The SIGCHLD handler has:
waitpid(-1, &status, WNOHANG | WUNTRACED);
upon return pid=0 and WIFEXITED=1
so, the process exited, but I can't get the pid?
I need the pid.
From the man page: "if WNOHANG was specified and one or more child(ren) specified by pid exist, but have not yet changed state, then 0 is returned"
But it seems the status has changed to exited.
The status is meaningless if the pid returned was 0. Think about it. A return of 0 means you have one or more children that have yet to change state. What would the state of a child that has yet to change state be? If there were multiple children, which child is the status code referencing?
This is analogous to checking errno on a successful call. Anything from a previous call can be in errno but it has nothing to do with the most recent successful call because errno is usually not set on success.
The return value of waitpid is the PID of the child that was waited for.