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, 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 .