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TIMES(2)                   Linux Programmer's Manual                  TIMES(2)



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 */
           };

       The tms_utime field contains the CPU time spent executing instructions of the call-
       ing  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 chil-
       dren.  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 grandchil-
       dren 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.

CONFORMING TO
       SVr4, 4.3BSD, POSIX.1-2001.

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 obsoles-
       cent.  It is obsolete now.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 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 gettimeofday(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.

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 passed the maximum value that
       can be stored in clockid_t.

SEE ALSO
       time(1), getrusage(2), wait(2), clock(3), sysconf(3), time(7)

COLOPHON
       This page is part of release 3.22 of the Linux man-pages project.  A description of
       the  project, and information about reporting bugs, can be found at http://www.ker-
       nel.org/doc/man-pages/.



Linux                             2008-06-25                          TIMES(2)

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