times(3) [osf1 man page]
times(3) Library Functions Manual times(3) NAME
times - Gets process and child process times LIBRARY
Standard C Library (libc.so, libc.a) SYNOPSIS
#include <sys/times.h> clock_t times( struct tms *buffer); Programs that are being developed for conformance to the AT&T System V Interface Definition must specify two #include statements, as fol- lows: #include <sys/types.h> #include <sys/times.h> STANDARDS
Interfaces documented on this reference page conform to industry standards as follows: times(): XPG4, XPG4-UNIX Refer to the standards(5) reference page for more information about industry standards and associated tags. PARAMETERS
Points to type tms structure space where system time information is stored. DESCRIPTION
The times() function fills the type tms structure space pointed to by the buffer parameter with time-accounting information. All time val- ues reported by this function are in hardware-dependent clock ticks. The times of a terminated child process are included in the tms_cutime and tms_cstime elements of the parent process when a wait function returns the process ID of that terminated child. The tms structure, which is defined in the sys/times.h header file, contains the following members: User time. The CPU time charged while executing user instructions of the calling process. System time. The CPU time charged during system execution on behalf of the calling process. User time, children. The sum of the tms_utime and the tms_cutime times of the child processes. System time, children. The sum of the tms_stime and the tms_cstime times of the child processes. When a child process does not wait for its children, its child-process times are not included in its times. This information comes from the calling process and each of its terminated child processes for which a wait function has been executed. RETURN VALUES
Upon successful completion, the times() function returns the elapsed real time since an arbitrary reference time in the past (for example, system start-up time). The reference time does not change from one invocation of times() within the process to another. The elapsed times are in units of 1/CLK_TCK seconds, where CLK_TCK is processor dependent. For application portability, the value of CLK_TCK should be queried using the sysconf() function (see sysconf(3)). The return value may overflow the possible range of type clock_t values. When the times() function fails, a value of (clock_t)-1 is returned. RELATED INFORMATION
Commands: cc(1) Functions: exec(2), fork(2), getrusage(2), profil(2), stime(3), sysconf(3), time(3), wait(2) Standards: standards(5) delim off times(3)
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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 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 par- ticular, 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 possi- ble 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 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 automati- cally 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 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 mea- sure 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 3.27 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. Linux 2008-06-25 TIMES(2)