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TIMES
Section: POSIX Programmer's Manual (3P)
Updated: 2003
Index
Return to Main Contents
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.
NAME
times - get process and waited-for child process times
SYNOPSIS
#include <sys/times.h>
clock_t times(struct tms * buffer);
DESCRIPTION
The times() function shall fill the tms structure pointed
to by buffer with time-accounting information.
The tms structure is defined in <sys/times.h>.
All times are measured in terms of the number of clock ticks used.
The times of a terminated child process shall be included in the tms_cutime
and tms_cstime elements of the parent
when wait() or waitpid() 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.
- *
-
The tms_utime structure member is the CPU time charged for the
execution of user instructions of the calling process.
- *
-
The tms_stime structure member is the CPU time charged for execution
by the system on behalf of the calling process.
- *
-
The tms_cutime structure member is the sum of the tms_utime
and tms_cutime times of the child
processes.
- *
-
The tms_cstime structure member is the sum of the tms_stime
and tms_cstime times of the child
processes.
RETURN VALUE
Upon successful completion, times() 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 times() within the process to
another. The return value may overflow the possible range of type
clock_t. If times() fails, (clock_t)-1 shall
be returned and errno set to indicate the error.
ERRORS
No errors are defined.
The following sections are informative.
EXAMPLES
Timing a Database Lookup
The following example defines two functions, start_clock() and
end_clock(), that are used to time a lookup. It
also defines variables of type clock_t and tms to measure
the duration of transactions. The start_clock()
function saves the beginning times given by the times() function.
The end_clock() function gets the ending times and
prints the difference between the two times.
-
#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);
}
/* 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);
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));
}
APPLICATION USAGE
Applications should use sysconf(_SC_CLK_TCK) to determine the
number of clock ticks per second as it may vary from system
to system.
RATIONALE
The accuracy of the times reported is intentionally left unspecified
to allow implementations flexibility in design, from
uniprocessor to multi-processor networks.
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 alarm().
If the type clock_t 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.
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.
FUTURE DIRECTIONS
None.
SEE ALSO
alarm(), exec(), fork(), sysconf(), time(),
wait(), the Base Definitions volume of IEEE Std 1003.1-2001,
<sys/times.h>
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 .
Index
- PROLOG
-
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- EXAMPLES
-
- Timing a Database Lookup
-
- APPLICATION USAGE
-
- RATIONALE
-
- FUTURE DIRECTIONS
-
- SEE ALSO
-
- COPYRIGHT
-
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