|
HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
|
PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
|
|
|
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.
The times() function shall fail if:
EOVERFLOW
The return value would overflow the range of clock_t.
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.1‐2017 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.1‐2017, sys_times.h(0p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 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 .
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 2017 TIMES(3P)
Pages that refer to this page: sys_times.h(0p), time(1p), clock(3p), exec(3p), fork(3p), getdate(3p), getrusage(3p), posix_spawn(3p), time(3p)
|
HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|