# waitid

## 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 obtain status information (see _Section_
           _2.13_ , _Status Information_) pertaining to termination, stop, and/or
           continue events in one of the caller's child processes.
    
           The _waitid_() function shall cause the calling thread to become
           blocked until an error occurs or status information becomes
           available to the calling thread that satisfies all of the
           following properties (``matching status information''):
    
            *  The status information is from one of the child processes in
               the set of child processes specified by the _idtype_ and _id_
               arguments.
    
            *  The state change in the status information matches one of the
               state change flags set in the _options_ argument.
    
           If matching status information is available prior to the call to
           _waitid_(), return shall be immediate. If matching status
           information is available for two or more child processes, the
           order in which their status is reported is unspecified.
    
           As described in _Section 2.13_ , _Status Information_ , the _waitid_()
           function consumes the status information it obtains unless the
           WNOWAIT flag is set in the _options_ argument.
    
           The behavior when multiple threads are blocked in _wait_(),
           _waitid_(), or _waitpid_() is described in _Section 2.13_ , _Status_
           _Information_.
    
           The _waitid_() function shall record the obtained status information
           in the structure pointed to by _infop_.  The fields of the structure
           pointed to by _infop_ shall be filled in as described under
           ``Pointer to a Function'' in _Section 2.4.3_ , _Signal Actions_.
    
           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



           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
                  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



           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_().
    
           As specified in _Consequences of Process Termination_ , if the
           calling process has SA_NOCLDWAIT set or has SIGCHLD set to
           SIG_IGN, then the termination of a child process will not cause
           status information to become available to a thread blocked in
           _wait_(), _waitid_(), or _waitpid_().  Thus, a thread blocked in one of
           the wait functions will remain blocked unless some other condition
           causes the thread to resume execution (such as an **[ECHILD]** failure
           due to no remaining children in the set of waited-for children).
    


## RATIONALE



           None.
    


## FUTURE DIRECTIONS



           None.
    


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