man-pages/man2/wait4.2

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.\" (c) 2004 bu Michael Kerrisk (mtk-manpages@gmx.net)
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.\" Modified Sat Jul 24 13:32:44 1993 by Rik Faith (faith@cs.unc.edu)
.\" Modified Mon Jun 23 14:09:52 1997 by aeb - add EINTR.
.\" Modified Tue Jul  7 12:26:42 1998 by aeb - changed return value wait3
.\" Modified 2004-11-11, Michael Kerrisk <mtk-manpages@gmx.net>
.\"	Rewrote much of this page, and removed much duplicated text, 
.\"		replacing with pointers to wait.2
.\"
.TH WAIT4 2  2004-11-11 "Linux" "Linux Programmer's Manual"
.SH NAME
wait3, wait4 \- wait for process to change state, BSD style
.SH SYNOPSIS
.nf
.B #include <sys/types.h>
.B #include <sys/time.h>
.B #include <sys/resource.h>
.B #include <sys/wait.h>
.sp
.BI "pid_t wait3(int *" "status" ", int " options ,
.BI "      struct rusage *" rusage );
.sp
.BI "pid_t wait4(pid_t " pid ", int *" status ", int " options ,
.BI "      struct rusage *" rusage );
.fi
.SH DESCRIPTION
The
.BR wait3 ()
and
.BR wait4 ()
system calls are similar to
.BR waitpid (2),
but additionally return resource usage information about the
child in the structure pointed to by
.IR rusage .
.PP
Other than the use of the
.I rusage
argument, the following
.BR wait3 ()
call:
.nf

    wait3(status, options, rusage);

.fi
is equivalent to:
.nf

    waitpid(-1, status, options);

.fi
Similarly, the following
.BR wait4 ()
call:
.nf

    wait4(pid, status, options, rusage);

.fi
is equivalent to:
.nf

    waitpid(pid, status, options);

.fi
In other words,
.BR wait3 ()
waits of any child, while
.BR wait4 ()
can be used to select a specific child, or children, on which to wait.
See
.BR wait (2)
for further details.
.PP
If
.I rusage
is not
.BR NULL ,
the
.I struct rusage
to which it points will be filled with accounting information
about the child.
See
.BR getrusage (2)
for details.
.SH "RETURN VALUE"
As for
.BR waitpid (2);
see
.BR wait (2).
.SH ERRORS
As for
.BR waitpid (2);
see
.BR wait (2).
.SH NOTES
Including
.I <sys/time.h>
is not required these days, but increases portability.
(Indeed,
.I <sys/resource.h>
defines the
.I rusage
structure with fields of type
.I struct timeval
defined in
.IR <sys/time.h> .)
.LP
The prototype for these functions is only available if
.B _BSD_SOURCE
is defined (either explicitly, or implicitly, by not defining
_POSIX_SOURCE or compiling with the -ansi flag).
.SH "CONFORMING TO"
SVr4, POSIX.1
.SH "SEE ALSO"
.BR fork (2),
.BR getrusage (2),
.BR sigaction (2),
.BR signal (2),
.BR wait (2),
.BR signal (7)