times() - Unix, Linux System Call
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NAME
times - get process times
SYNOPSIS
#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 */
};
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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)
is 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.
For 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.
The return value may overflow the possible range of type
clock_t. On error, (clock_t) -1 is returned, and
errno is set appropriately.
NOTES
The number of clock ticks per second can be obtained using
sysconf(_SC_CLK_TCK);
In POSIX-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 It is obsolete now.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 only happen
if the calling process
wait()s on its children.
This non-conformance 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 behaviour, and most
other Unix implementations require a non-NULL value for
buf.
Note that
clock(3)
returns values of type
clock_t that are not measured in clock ticks
but in
CLOCKS_PER_SEC. CONFORMING TO
SVr4, 4.3BSD, POSIX.1-2001.
HISTORICAL NOTES
SVr1-3 returns
long and the struct members are of type
time_t although they store clock ticks, not seconds since the epoch. V7 used
long for the struct members, because it had no type
time_t yet.
On older systems the number of clock ticks per second is given
by the variable HZ.
SEE ALSO
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