WAITID(3)                  POSIX Programmer's Manual                 WAITID(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.


NAME
       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);

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
       termination.

       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
                   continued 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
       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 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
       specified 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
              processes.

       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
       applications 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
       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 .

       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.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2013                            WAITID(3)
