WAIT(2-SysV)        RISC/os Reference Manual         WAIT(2-SysV)



NAME
     wait, wait2 - wait for child process to stop or terminate

SYNOPSIS
     #include <bsd/sys/types.h>

     int wait (stat_loc)
     int *stat_loc;

     #include <sys/wait.h>
     int wait2 (stat_loc, options)
     int *stat_loc, options;

DESCRIPTION
     wait suspends the calling process until one of the immediate
     children terminates or until a child that is being traced
     stops, because it has hit a break point.  The wait system
     call will return prematurely if a signal is received and if
     a child process stopped or terminated prior to the call on
     wait, return is immediate.  wait2 is similar to wait, except
     that it can be given options to effect its behavior.

     If stat_loc is non-zero, 16 bits of information called
     status are stored in the low order 16 bits of the location
     pointed to by stat_loc.  status can be used to differentiate
     between stopped and terminated child processes and if the
     child process terminated, status identifies the cause of
     termination and passes useful information to the parent.
     This is accomplished in the following manner:

          If the child process stopped, the high order 8 bits of
          status will contain the number of the signal that
          caused the process to stop and the low order 8 bits
          will be set equal to 0177.

          If the child process terminated due to an exit call,
          the low order 8 bits of status will be zero and the
          high order 8 bits will contain the low order 8 bits of
          the argument that the child process passed to exit [see
          exit(2)].

          If the child process terminated due to a signal, the
          high order 8 bits of status will be zero and the low
          order 8 bits will contain the number of the signal that
          caused the termination. In addition, if the low order
          seventh bit (i.e., bit 200) is set, a ``core image''
          will have been produced [see signal(2)].

     The options argument is a flag which may have bits set to
     change the behavior of wait2. Setting the WNOHANG bit causes
     wait2 to return immediately, even if no children are ready
     to be waited for.  At the current time, only WNOHANG is



                         Printed 1/15/91                   Page 1

WAIT(2-SysV)        RISC/os Reference Manual         WAIT(2-SysV)



     implemented.

     If a parent process terminates without waiting for its child
     processes to terminate, the parent process ID of each child
     process is set to 1. This means the initialization process
     inherits the child processes [see intro(2)].

ERRORS
     wait will fail and return immediately if the following is
     true:

     [ECHILD]       The calling process has no existing
                    unwaited-for child processes.

SEE ALSO
     exec(2), exit(2), fork(2), intro(2), pause(2), ptrace(2),
     signal(2).

WARNING
     wait fails and its actions are undefined if stat_loc points
     to an invalid address.

     See NOTES in signal(2) and WARNING in sigset(2).


DIAGNOSTICS
     If wait returns due to the receipt of a signal, a value of
     -1 is returned to the calling process and errno is set to
     EINTR. If wait returns due to a stopped or terminated child
     process, the process ID of the child is returned to the cal-
     ling process.  Otherwise, a value of -1 is returned and
     errno is set to indicate the error.























 Page 2                  Printed 1/15/91