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waitid(2) waitid(2)

NAME

waitid - wait for child process to change state

SYNOPSIS

#include <sys/wait.h>

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

DESCRIPTION

The waitid() function 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 are used to specify which children waitid() will wait for.

If idtype is P_PID, waitid() will wait for the child with a process ID equal to (pid_t)pid.

If idtypeis P_PGID, waitid() will wait for any child with a process group ID equal to (pid_t)pid.

If idtypeis P_ALL, waitid() will wait for any children and id is ignored.

The options argument is used to specify which state changes

waitid() will wait for. It is formed by

OR-ing together one or more of the following ﬂags:

WEXITED Wait for processes that have exited.

WSTOPPED Status will be returned for any child that has stopped upon receipt of a sig-

nal.

WCONTINUED Status will be returned for any child that was stopped and has been contin-

ued.

WNOHANG Return immediately if there are no children to wait for.

WNOWAIT Keep the process whose status is returned in infop in a waitable state. This

will not affect the state of the process; the process may be waited for again

after this call completes.

The infop argument must point to a siginfo_t structure. 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 will be ﬁlled in by the system with the status of the process. The si_signo member will

always be equal to

SIGCHLD.

RETURN VALUE

If waitid() returns due to the change of state of one of its children, 0 is returned. Otherwise, −1is

returned and

errno is set to indicate the error.

ERRORS

The waitid() function will fail if:

[ECHILD] The calling process has no existing unwaited-for child processes.

[EINTR] The waitid() function was interrupted due to the receipt of a signal by the calling

process.

[EINVAL] An invalid value was speciﬁed for options,oridtype and id specify an invalid set of

processes.

APPLICATION USAGE

Threads Considerations

In a multi-threaded application, only the calling thread is suspended by

waitid().

waitid() will not return until all threads in the process have reached the desired state. For example, if

the WEXITED, WSTOPPED or WCONTINUED options are speciﬁed, waitid() will not return until all

threads in the process have terminated, stopped or continued respectively.