man-pages/man2/wait4.2

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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.
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.\"		replacing with pointers to wait.2
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.TH WAIT4 2  2007-07-26 "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
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.BR wait3 ():
_BSD_SOURCE
.br
.BR wait4 ():
_BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500
.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 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).
.SH ERRORS
As for
.BR waitpid (2).
.SH "CONFORMING TO"
4.3BSD
.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> .)
.SH "SEE ALSO"
.BR fork (2),
.BR getrusage (2),
.BR sigaction (2),
.BR signal (2),
.BR wait (2),
.BR signal (7)