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 signal.
- WCONTINUED
Status will be returned for any child that was stopped and has been
continued.
- 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, -1 is 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,
or
idtype
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.
CHANGE HISTORY
First released in Issue 4, Version 2.
Printable version
