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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(), 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.
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
The times() function shall fail if:
EOVERFLOW
The return value would overflow the range of clock_t.
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 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.
FUTURE DIRECTIONS
None.
SEE ALSO
alarm(), exec, fork(), sysconf(), time(), wait(), waitid()
The Base Definitions volume of POSIX.1‐2017, <sys_times.h>
COPYRIGHT
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 .