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WAIT(2)                       System Calls Manual                      WAIT(2)



NAME
       await, wait, waitpid - wait for a process to exit

SYNOPSIS
       #include <u.h>
       #include <libc.h>

       Waitmsg*  wait(void)

       int       waitpid(void)

       int       await(char *s, int n)

DESCRIPTION
       Wait  causes  a  process to wait for any child process (see fork(2)) to
       exit.  It returns a Waitmsg holding information about the exited child.
       A Waitmsg has this structure:

              typedef
              struct Waitmsg
              {
                    int pid;              /* of loved one */
                    ulong time[3];        /* of loved one & descendants */
                    char *msg;
              } Waitmsg;

       Pid  is  the  child's process id.  The time array contains the time the
       child and its descendants spent in user code, the time spent in  system
       calls, and the child's elapsed real time, all in units of milliseconds.
       Msg contains the message that the child specified in exits(2).   For  a
       normal  exit, msg[0] is zero, otherwise msg is the exit string prefixed
       by the process name, a blank, the process id, and a colon.

       If there are no more children to wait for,  wait  returns  immediately,
       with return value nil.

       The  Waitmsg  structure  is  allocated by malloc(2) and should be freed
       after use.  For programs that only need the pid of the exiting program,
       waitpid returns just the pid and discards the rest of the information.

       The underlying system call is await, which fills in the n-byte buffer s
       with a textual representation of  the  pid,  times,  and  exit  string.
       There is no terminal NUL.  The return value is the length, in bytes, of
       the data.

       The buffer filled in by await may be parsed  (after  appending  a  NUL)
       using  tokenize (see getfields(2)); the resulting fields are, in order,
       pid, the three times, and the exit string, which will be '' for  normal
       exit.   If  the  representation is longer than n bytes, it is truncated
       but, if possible, properly formatted.  The information  that  does  not
       fit  in  the  buffer  is  discarded, so a subsequent call to await will
       return the information about the next exiting child, not the  remainder
       of  the  truncated message.  In other words, each call to await returns
       the information about one child, blocking if necessary if no child  has
       exited.

       If the calling process has no living children, await and waitpid return
       -1.

SOURCE
       /sys/src/libc/9syscall
       /sys/src/libc/9sys

SEE ALSO
       fork(2), exits(2), the wait file in proc(3)

DIAGNOSTICS
       These routines set errstr.



                                                                       WAIT(2)