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TIMES(3P) POSIX Programmer's Manual TIMES(3P)
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.
times — get process and waited-for child process times
#include <sys/times.h>
clock_t times(struct tms *buffer);
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(),
waitid(), 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.
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.
No errors are defined.
The following sections are informative.
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));
}
Applications should use sysconf(_SC_CLK_TCK) to determine the number
of clock ticks per second as it may vary from system to system.
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(3p).
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 POSIX.1‐2008 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.
None.
alarm(3p), exec(1p), fork(3p), sysconf(3p), time(3p), wait(3p),
waitid(3p)
The Base Definitions volume of POSIX.1‐2008, sys_times.h(0p)
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) 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.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 TIMES(3P)
Pages that refer to this page: sys_times.h(0p), time(1p), exec(3p), fork(3p), getdate(3p), getrusage(3p), posix_spawn(3p), time(3p)