WAITID(3P) POSIX Programmer's Manual WAITID(3P)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.
NAMEwaitid — 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);
DESCRIPTION
The waitid() 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 infop. The
fields of the structure pointed to by infop are filled in as described
for the SIGCHLD signal in <signal.h>. If a child process changed state
prior to the call to waitid(), waitid() shall return immediately. If
more than one thread is suspended in wait(), waitid(), or waitpid()
waiting for termination of the same process, exactly one thread shall
return the process status at the time of the target process termina‐
tion.
The idtype and id arguments are used to specify which children waitid()
waits for.
If idtype is P_PID, waitid() shall wait for the child with a process ID
equal to (pid_t)id.
If idtype is P_PGID, waitid() shall wait for any child with a process
group ID equal to (pid_t)id.
If idtype is P_ALL, waitid() shall wait for any children and id is
ignored.
The options argument is used to specify which state changes waitid()
shall wait for. It is formed by OR'ing together the following flags:
WCONTINUED Status shall be returned for any continued child process
whose status either has not been reported since it contin‐
ued from a job control stop or has been reported only by
calls to waitid() with the WNOWAIT flag set.
WEXITED Wait for processes that have exited.
WNOHANG Do not hang if no status is available; return immediately.
WNOWAIT Keep the process whose status is returned in 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.
WSTOPPED 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 waitid() with the WNOWAIT flag set.
Applications shall specify at least one of the flags WEXITED, WSTOPPED,
or WCONTINUED to be OR'ed in with the options argument.
The application shall ensure that the infop argument points to a sig‐
info_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 shall be filled in by
the system with the status of the process; the si_signo member shall be
set equal to SIGCHLD. If waitid() returns because WNOHANG was speci‐
fied and status is not available for any process specified by idtype
and id, then the si_signo and si_pid members of the structure pointed
to by infop shall be set to zero and the values of other members of the
structure are unspecified.
RETURN VALUE
If WNOHANG was specified and status is not available for any process
specified by idtype and id, 0 shall be returned. If waitid() returns
due to the change of state of one of its children, 0 shall be returned.
Otherwise, −1 shall be returned and errno set to indicate the error.
ERRORS
The waitid() function shall fail if:
ECHILD The calling process has no existing unwaited-for child pro‐
cesses.
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.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
Calls to waitid() with 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 system()). For this reason it is recommended that portable applica‐
tions not use waitid() with idtype of P_ALL. See also APPLICATION USAGE
for wait().
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
exec, exit(), wait()
The Base Definitions volume of POSIX.1‐2008, <signal.h>, <sys_wait.h>
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 Electri‐
cal 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 .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the source
files to man page format. To report such errors, see https://www.ker‐
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 WAITID(3P)
