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.TH WAITID "3P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.

.SH NAME
waitid
\(em wait for a child process to change state
.SH SYNOPSIS
.LP
.nf
#include <sys/wait.h>
.P
int waitid(idtype_t \fIidtype\fP, id_t \fIid\fP, siginfo_t *\fIinfop\fP, int \fIoptions\fP);
.fi
.SH DESCRIPTION
The
\fIwaitid\fR()
function shall suspend the calling thread until one child of the
process containing the calling thread changes state. It records the
current state of a child in the structure pointed to by
.IR infop .
The fields of the structure pointed to by
.IR infop
are filled in as described for the SIGCHLD signal in
.IR <signal.h> .
If a child process changed state prior to the call to
\fIwaitid\fR(),
\fIwaitid\fR()
shall return immediately. If more than one thread is suspended in
\fIwait\fR(),
\fIwaitid\fR(),
or
\fIwaitpid\fR()
waiting for termination of the same process, exactly one thread shall
return the process status at the time of the target process termination.
.P
The
.IR idtype
and
.IR id
arguments are used to specify which children
\fIwaitid\fR()
waits for.
.P
If
.IR idtype
is P_PID,
\fIwaitid\fR()
shall wait for the child with a process ID equal to
(\fBpid_t\fP)\fIid\fR.
.P
If
.IR idtype
is P_PGID,
\fIwaitid\fR()
shall wait for any child with a process group ID equal to
(\fBpid_t\fP)\fIid\fR.
.P
If
.IR idtype
is P_ALL,
\fIwaitid\fR()
shall wait for any children and
.IR id
is ignored.
.P
The
.IR options
argument is used to specify which state changes
\fIwaitid\fR()
shall wait for. It is formed by OR'ing together the following flags:
.IP WCONTINUED 12
Status shall be returned for any continued child process whose status
either has not been reported since it continued from a job control stop
or has been reported only by calls to
\fIwaitid\fR()
with the WNOWAIT flag set.
.IP WEXITED 12
Wait for processes that have exited.
.IP WNOHANG 12
Do not hang if no status is available; return immediately.
.IP WNOWAIT 12
Keep the process whose status is returned in
.IR infop
in a waitable state. This shall not affect the state of the process; the
process may be waited for again after this call completes.
.IP WSTOPPED 12
Status shall be returned for any child that has stopped upon receipt of
a signal, and whose status either has not been reported since it stopped
or has been reported only by calls to
\fIwaitid\fR()
with the WNOWAIT flag set.
.P
Applications shall specify at least one of the flags WEXITED, WSTOPPED,
or WCONTINUED to be OR'ed in with the
.IR options
argument.
.P
The application shall ensure that the
.IR infop
argument points to a
.BR siginfo_t
structure. If
\fIwaitid\fR()
returns because a child process was found that satisfied the conditions
indicated by the arguments
.IR idtype
and
.IR options ,
then the structure pointed to by
.IR infop
shall be filled in by the system with the status of the process; the
.IR si_signo
member shall be set equal to SIGCHLD.
If
\fIwaitid\fR()
returns because WNOHANG was specified and status is not available for
any process specified by
.IR idtype
and
.IR id ,
then the
.IR si_signo
and
.IR si_pid
members of the structure pointed to by
.IR infop
shall be set to zero and the values of other members of the structure
are unspecified.
.SH "RETURN VALUE"
If WNOHANG was specified and status is not available for any process
specified by
.IR idtype
and
.IR id ,
0 shall be returned. If
\fIwaitid\fR()
returns due to the change of state of one of its children, 0 shall be
returned. Otherwise, \(mi1 shall be returned and
.IR errno
set to indicate the error.
.SH ERRORS
The
\fIwaitid\fR()
function shall fail if:
.TP
.BR ECHILD
The calling process has no existing unwaited-for child processes.
.TP
.BR EINTR
The
\fIwaitid\fR()
function was interrupted by a signal.
.TP
.BR EINVAL
An invalid value was specified for
.IR options ,
or
.IR idtype
and
.IR id
specify an invalid set of processes.
.LP
.IR "The following sections are informative."
.SH EXAMPLES
None.
.SH "APPLICATION USAGE"
Calls to
\fIwaitid\fR()
with
.IR idtype
equal to P_ALL will collect information about any child process. This
may result in interactions with other interfaces that may be waiting
for their own children (such as by use of
\fIsystem\fR()).
For this reason it is recommended that portable applications not use
\fIwaitid\fR()
with idtype of P_ALL. See also APPLICATION USAGE for
\fIwait\fR().
.SH RATIONALE
None.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fIexec\fR\^",
.IR "\fIexit\fR\^(\|)",
.IR "\fIwait\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2008,
.IR "\fB<signal.h>\fP",
.IR "\fB<sys_wait.h>\fP"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.unix.org/online.html .

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