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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.
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 fol-
       lowing 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 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
       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 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
       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,  Copyright  (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.opengroup.org/unix/online.html .

IEEE/The Open Group                  2003                           WAITID(3P)