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 wait-
pid() 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 exe-
cution 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, sys-
tem 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.
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 par-
ent 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 over-
flows in somewhat more than a year if there are 60 clock ticks per sec-
ond, 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.
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 .
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