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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.  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)