waitid(2)

waitid -- wait for child process to change state

Synopsis

   #include <sys/types.h>
   #include <wait.h>
   
   int waitid(idtype_t idtype, id_t id, siginfo_t *infop, int options);

Description

waitid suspends the calling process until one of its children changes state. It records the current state of a child in the structure pointed to by infop. If a child process changed state prior to the call to waitid, waitid returns immediately.

The idtype and id arguments specify which children waitid is to wait for.

If idtype is P_PID, waitid waits for the child with a process ID equal to (pid_t) id.
If idtype is P_PGID, waitid waits for any child with a process group ID equal to (pid_t) id.
If idtype is P_ALL, waitid waits for any children and id is ignored.

The options argument is used to specify which state changes waitid is to wait for. It is formed by an OR of any of the following flags:

WEXITED: Wait for process(es) to exit.
WTRAPPED: Wait for traced process(es) to become trapped or reach a breakpoint [see ptrace(2)].
WSTOPPED: Wait for and return the process status of any child that has stopped upon receipt of a signal.
WCONTINUED: Return the status for any child that was stopped and has been continued.
WNOHANG: Return immediately.
WNOWAIT: Keep the process in a waitable state. This will not affect the state of the process on subsequent waits.

infop must point to a siginfo_t structure, as defined in siginfo(5). siginfo_t is filled in by the system with the status of the process being waited for.

Return values

If waitid returns due to a change of state of one of its children, it returns 0. Otherwise, waitid returns -1 and sets errno to identify the error.

Errors

In the following conditions, waitid fails and sets errno to:

EFAULT: infop points to an invalid address.
EINTR: waitid was interrupted due to the receipt of a signal by the calling process.
EINVAL: 0 or another invalid value was specified for options.
EINVAL: idtype and id specify an invalid set of processes.
ECHILD: The set of processes specified by idtype and id does not contain any unwaited-for processes.

References

exec(2), exit(2), fork(2), intro(2), pause(2), ptrace(2), sigaction(2), siginfo(5), signal(2), wait(2), waitpid(2)

Notices

Considerations for threads programming

While one thread is blocked, siblings might still be executing.