CODEWITHSUNDEEP
clinuxpidwaitpid
donkon
donkon

Reputation: 919

waitpid returns pid=0 and WIFEXITED=1 how to get pid?

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.

Upvotes: 3

Views: 3994

Answers (2)

Duck
Duck

Reputation: 27542

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.

Upvotes: 5

Kerrek SB
Kerrek SB

Reputation: 476950

The return value of waitpid is the PID of the child that was waited for.

Upvotes: 0

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