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 (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

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. 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() 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 one
       or more of the following flags:

       WEXITED
              Wait for processes that have exited.

       WSTOPPED
              Status shall be returned for any child that has stopped upon receipt of a signal.

       WCONTINUED
              Status shall 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 shall not affect  the  state  of  the
              process; the process may be waited for again after this call completes.


       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 always be equal to
       SIGCHLD.

RETURN VALUE
       If WNOHANG was specified and there are no children to wait for, 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
       None.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       exec(), exit(), wait(), the Base Definitions volume of IEEE Std 1003.1-2001, <sys/wait.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003  Edition,  Standard  for
       Information  Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copy-
       right (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. 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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                    WAITID(3P)