times (2)
Leading comments
Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992 %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice id...
NAME
times - get process timesSYNOPSIS
#include <sys/times.h>clock_t times(struct tms *buf);
DESCRIPTION
times() stores the current process times in the struct tms that buf points to. The struct tms is as defined in <sys/times.h>:
struct tms {
clock_t tms_utime; /* user time */
clock_t tms_stime; /* system time */
clock_t tms_cutime; /* user time of children */
clock_t tms_cstime; /* system time of children */
};
The tms_utime field contains the CPU time spent executing instructions of the calling process. The tms_stime field contains the CPU time spent in the system while executing tasks on behalf of the calling process. The tms_cutime field contains the sum of the tms_utime and tms_cutime values for all waited-for terminated children. The tms_cstime field contains the sum of the tms_stime and tms_cstime values for all waited-for terminated children.
Times for terminated children (and their descendants) are added in at the moment wait(2) or waitpid(2) returns their process ID. In particular, times of grandchildren that the children did not wait for are never seen.
All times reported are in clock ticks.
RETURN VALUE
times() returns the number of clock ticks that have elapsed since an arbitrary point in the past. The return value may overflow the possible range of type clock_t. On error, (clock_t) -1 is returned, and errno is set appropriately.ERRORS
- EFAULT
- tms points outside the process's address space.
CONFORMING TO
POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.NOTES
The number of clock ticks per second can be obtained using:sysconf(_SC_CLK_TCK);
In POSIX.1-1996 the symbol CLK_TCK (defined in <time.h>) is mentioned as obsolescent. It is obsolete now.
In Linux kernel versions before 2.6.9,
if the disposition of
SIGCHLD
is set to
SIG_IGN,
then the times of terminated children
are automatically included in the
tms_cstime
and
tms_cutime
fields, although POSIX.1-2001 says that this should happen
only if the calling process
wait(2)s
on its children.
This nonconformance is rectified in Linux 2.6.9 and later.
On Linux, the
buf
argument can be specified as NULL, with the result that
times()
just returns a function result.
However, POSIX does not specify this behavior, and most
other UNIX implementations require a non-NULL value for
buf.
Note that
clock(3)
also returns a value of type
clock_t,
but this value is measured in units of
CLOCKS_PER_SEC,
not the clock ticks used by
times().
On Linux, the "arbitrary point in the past" from which the return value of
times()
is measured has varied across kernel versions.
On Linux 2.4 and earlier this point is the moment the system was booted.
Since Linux 2.6, this point is (2^32/HZ) - 300
(i.e., about 429 million) seconds before system boot time.
This variability across kernel versions (and across UNIX implementations),
combined with the fact that the returned value may overflow the range of
clock_t,
means that a portable application would be wise to avoid using this value.
To measure changes in elapsed time, use
clock_gettime(2)
instead.