man-pages/man3p/times.3p

.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "TIMES" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" times 
.SH 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.
.SH NAME
times \- get process and waited-for child process times
.SH SYNOPSIS
.LP
\fB#include <sys/times.h>
.br
.sp
clock_t times(struct tms *\fP\fIbuffer\fP\fB);
.br
\fP
.SH DESCRIPTION
.LP
The \fItimes\fP() function shall fill the \fBtms\fP structure pointed
to by \fIbuffer\fP with time-accounting information.
The \fBtms\fP structure is defined in \fI<sys/times.h>\fP.
.LP
All times are measured in terms of the number of clock ticks used.
.LP
The times of a terminated child process shall be included in the \fItms_cutime\fP
and \fItms_cstime\fP elements of the parent
when \fIwait\fP() or \fIwaitpid\fP() returns the
process ID of this terminated child. If a child process has not waited
for its children, their times shall not be included in its
times.
.IP " *" 3
The \fItms_utime\fP structure member is the CPU time charged for the
execution of user instructions of the calling process.
.LP
.IP " *" 3
The \fItms_stime\fP structure member is the CPU time charged for execution
by the system on behalf of the calling process.
.LP
.IP " *" 3
The \fItms_cutime\fP structure member is the sum of the \fItms_utime\fP
and \fItms_cutime\fP times of the child
processes.
.LP
.IP " *" 3
The \fItms_cstime\fP structure member is the sum of the \fItms_stime\fP
and \fItms_cstime\fP times of the child
processes.
.LP
.SH RETURN VALUE
.LP
Upon successful completion, \fItimes\fP() shall return the elapsed
real time, in clock ticks, since an arbitrary point in the
past (for example, system start-up time). This point does not change
from one invocation of \fItimes\fP() within the process to
another. The return value may overflow the possible range of type
\fBclock_t\fP. If \fItimes\fP() fails, (\fBclock_t\fP)-1 shall
be returned and \fIerrno\fP set to indicate the error.
.SH ERRORS
.LP
No errors are defined.
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.SS Timing a Database Lookup
.LP
The following example defines two functions, \fIstart_clock\fP() and
\fIend_clock\fP(), that are used to time a lookup. It
also defines variables of type \fBclock_t\fP and \fBtms\fP to measure
the duration of transactions. The \fIstart_clock\fP()
function saves the beginning times given by the \fItimes\fP() function.
The \fIend_clock\fP() function gets the ending times and
prints the difference between the two times.
.sp
.RS
.nf

\fB#include <sys/times.h>
#include <stdio.h>
\&...
void start_clock(void);
void end_clock(char *msg);
\&...
static clock_t st_time;
static clock_t en_time;
static struct tms st_cpu;
static struct tms en_cpu;
\&...
void
start_clock()
{
    st_time = times(&st_cpu);
}
.sp

/* This example assumes that the result of each subtraction
   is within the range of values that can be represented in
   an integer type. */
void
end_clock(char *msg)
{
    en_time = times(&en_cpu);
.sp

    fputs(msg,stdout);
    printf("Real Time: %jd, User Time %jd, System Time %jd\\n",
        (intmax_t)(en_time - st_time),
        (intmax_t)(en_cpu.tms_utime - st_cpu.tms_utime),
        (intmax_t)(en_cpu.tms_stime - st_cpu.tms_stime));
}
\fP
.fi
.RE
.SH APPLICATION USAGE
.LP
Applications should use \fIsysconf\fP(_SC_CLK_TCK) to determine the
number of clock ticks per second as it may vary from system
to system.
.SH RATIONALE
.LP
The accuracy of the times reported is intentionally left unspecified
to allow implementations flexibility in design, from
uniprocessor to multi-processor networks.
.LP
The inclusion of times of child processes is recursive, so that a
parent process may collect the total times of all of its
descendants. But the times of a child are only added to those of its
parent when its parent successfully waits on the child. Thus,
it is not guaranteed that a parent process can always see the total
times of all its descendants; see also the discussion of the
term ``realtime'' in \fIalarm\fP().
.LP
If the type \fBclock_t\fP is defined to be a signed 32-bit integer,
it overflows in somewhat more than a year if there are 60
clock ticks per second, or less than a year if there are 100. There
are individual systems that run continuously for longer than
that. This volume of IEEE\ Std\ 1003.1-2001 permits an implementation
to make the reference point for the returned value be
the start-up time of the process, rather than system start-up time.
.LP
The term ``charge'' in this context has nothing to do with billing
for services. The operating system accounts for time used in
this way. That information must be correct, regardless of how that
information is used.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIalarm\fP(), \fIexec\fP(), \fIfork\fP(), \fIsysconf\fP(), \fItime\fP(),
\fIwait\fP(), the Base Definitions volume of IEEE\ Std\ 1003.1-2001,
\fI<sys/times.h>\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .