получить время обработки (get process times)
Имя (Name)
times - get process times
Синопсис (Synopsis)
#include <sys/times.h>
clock_t times(struct tms *buf);
Описание (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 executing inside the kernel while
performing 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.
Возвращаемое значение (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 to indicate the error.
Ошибки (Error)
EFAULT tms points outside the process's address space.
Стандарты (Conforming to)
POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
Примечание (Note)
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 It is obsolete now.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 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.
Historical
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.
Ошибки (баги) (Bugs)
A limitation of the Linux system call conventions on some
architectures (notably i386) means that on Linux 2.6 there is a
small time window (41 seconds) soon after boot when times() can
return -1, falsely indicating that an error occurred. The same
problem can occur when the return value wraps past the maximum
value that can be stored in clock_t.
Смотри также (See also)
time(1), getrusage(2), wait(2), clock(3), sysconf(3), time(7)
