PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

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

PROLOG         top

       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         top

       waitid — wait for a child process to change state

SYNOPSIS         top

       #include <sys/wait.h>

       int waitid(idtype_t idtype, id_t id, siginfo_t *infop, int options);

DESCRIPTION         top

       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         top

       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         top

       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         top

       None.

APPLICATION USAGE         top

       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         top

       None.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       exec(1p), exit(3p), wait(3p)

       The Base Definitions volume of POSIX.1‐2008, signal.h(0p),
       sys_wait.h(0p)

COPYRIGHT         top

       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(3P)