waitid()

Wait for a child process to change state

Synopsis:

#include <sys/wait.h>

int waitid( idtype_t idtype,
            id_t id,
            siginfo_t * infop,
            int options );

Arguments:

idtype

Which children you want to wait for:

• P_PID — the child with a process ID of (pid_t)id.
• P_PGID — any child with a process group ID equal to (pid_t)id.
• P_ALL — any child; id is ignored.

id

The process or process group ID that you want to wait for, depending on the value of idtype.

infop

A pointer to a siginfo_t structure, as defined in <sys/siginfo.h>, where the function can store the current state of the child; see below.

options

A combination of zero or more of the following flags:

• WCONTINUED — return the status for any child that was stopped and has been continued.
• WEXITED — wait for the process(es) to exit.
• WNOHANG — return immediately if there are no children to wait for.
• WNOWAIT — keep the process in a waitable state. This doesn't affect the state of the process; the process may be waited for again after this call completion.
• WSTOPPED — wait for and return the process status of any child that has stopped because it received a signal.
• WUNTRACED — report the status of a stopped child process.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The waitid() function suspends the calling thread 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.

If waitid() returns because a child process was found that satisfied the conditions indicated by the arguments idtype and options, then the structure pointed to by infop is filled in by the system with the status of the process. The si_signo member is always SIGCHLD.

If idtype is P_ALL and options is WEXITED|WTRAPPED, waitid() is equivalent to wait().

Returns:

0

One of the children changed its state. If WNOHANG was used, 0 can be returned (indicating no error); however, no children may have changed state if info->si_pid is 0.

-1

An error occurred (errno is set).

Errors:

ECHILD

The set of processes specified by idtype and id doesn't contain any unwaited-for processes.

EFAULT

The infop argument points to an illegal address.

EINTR

The waitid() function was interrupted by a signal.

EINVAL

An invalid value was specified for options, or idtype and id specify an invalid set of processes.

Classification:

POSIX 1003.1 XSI

See also:

execl(), execle(), execlp(), execlpe(), execv(), execve(), execvp(), execvpe(), exit(), fork(), pause(), sigaction(), signal(), wait(), wait3(), wait4(), waitpid()