times — get process times
#include <sys/times.h>
clock_t times( |
struct tms * | buf) ; |
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) 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.
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.
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 It is obsolete now.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(2)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
.
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.
time(1), getrusage(2), wait(2), clock(3), sysconf(3), time(7)
|