1TIMES(3P)                  POSIX Programmer's Manual                 TIMES(3P)
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PROLOG

6       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
7       implementation of this interface may differ (consult the  corresponding
8       Linux  manual page for details of Linux behavior), or the interface may
9       not be implemented on Linux.
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11

NAME

13       times — get process and waited-for child process times
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SYNOPSIS

16       #include <sys/times.h>
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18       clock_t times(struct tms *buffer);
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DESCRIPTION

21       The times() function shall fill the tms structure pointed to by  buffer
22       with  time-accounting  information.  The  tms  structure  is defined in
23       <sys/times.h>.
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25       All times are measured in terms of the number of clock ticks used.
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27       The times of a terminated  child  process  shall  be  included  in  the
28       tms_cutime and tms_cstime elements of the parent when wait(), waitid(),
29       or waitpid() returns the process ID of  this  terminated  child.  If  a
30       child process has not waited for its children, their times shall not be
31       included in its times.
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33        *  The tms_utime structure member is the CPU time charged for the exe‐
34           cution of user instructions of the calling process.
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36        *  The  tms_stime  structure member is the CPU time charged for execu‐
37           tion by the system on behalf of the calling process.
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39        *  The tms_cutime structure member is the sum  of  the  tms_utime  and
40           tms_cutime times of the child processes.
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42        *  The  tms_cstime  structure  member  is the sum of the tms_stime and
43           tms_cstime times of the child processes.
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RETURN VALUE

46       Upon successful completion, times() shall return the elapsed real time,
47       in clock ticks, since an arbitrary point in the past (for example, sys‐
48       tem start-up time). This point does not change from one  invocation  of
49       times()  within  the  process to another. The return value may overflow
50       the possible range of type  clock_t.   If  times()  fails,  (clock_t)−1
51       shall be returned and errno set to indicate the error.
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ERRORS

54       No errors are defined.
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56       The following sections are informative.
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EXAMPLES

59   Timing a Database Lookup
60       The   following   example  defines  two  functions,  start_clock()  and
61       end_clock(), that are used to time a lookup. It also defines  variables
62       of  type  clock_t  and tms to measure the duration of transactions. The
63       start_clock() function saves the beginning times given by  the  times()
64       function. The end_clock() function gets the ending times and prints the
65       difference between the two times.
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67           #include <sys/times.h>
68           #include <stdio.h>
69           ...
70           void start_clock(void);
71           void end_clock(char *msg);
72           ...
73           static clock_t st_time;
74           static clock_t en_time;
75           static struct tms st_cpu;
76           static struct tms en_cpu;
77           ...
78           void
79           start_clock()
80           {
81               st_time = times(&st_cpu);
82           }
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84           /* This example assumes that the result of each subtraction
85              is within the range of values that can be represented in
86              an integer type. */
87           void
88           end_clock(char *msg)
89           {
90               en_time = times(&en_cpu);
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92               fputs(msg,stdout);
93               printf("Real Time: %jd, User Time %jd, System Time %jd\n",
94                   (intmax_t)(en_time - st_time),
95                   (intmax_t)(en_cpu.tms_utime - st_cpu.tms_utime),
96                   (intmax_t)(en_cpu.tms_stime - st_cpu.tms_stime));
97           }
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APPLICATION USAGE

100       Applications should use sysconf(_SC_CLK_TCK) to determine the number of
101       clock ticks per second as it may vary from system to system.
102

RATIONALE

104       The accuracy of the times reported is intentionally left unspecified to
105       allow implementations  flexibility  in  design,  from  uniprocessor  to
106       multi-processor networks.
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108       The  inclusion of times of child processes is recursive, so that a par‐
109       ent process may collect the total times of all of its descendants.  But
110       the  times  of  a  child are only added to those of its parent when its
111       parent successfully waits on the child. Thus, it is not guaranteed that
112       a parent process can always see the total times of all its descendants;
113       see also the discussion of the term ``realtime'' in alarm().
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115       If the type clock_t is defined to be a signed 32-bit integer, it  over‐
116       flows in somewhat more than a year if there are 60 clock ticks per sec‐
117       ond, or less than a year if there are 100. There are individual systems
118       that run continuously for longer than that. This volume of POSIX.1‐2008
119       permits an implementation to make the reference point for the  returned
120       value  be the start-up time of the process, rather than system start-up
121       time.
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123       The term ``charge'' in this context has nothing to do with billing  for
124       services. The operating system accounts for time used in this way. That
125       information must be correct, regardless  of  how  that  information  is
126       used.
127

FUTURE DIRECTIONS

129       None.
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SEE ALSO

132       alarm(), exec, fork(), sysconf(), time(), wait(), waitid()
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134       The Base Definitions volume of POSIX.1‐2008, <sys_times.h>
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137       Portions  of  this text are reprinted and reproduced in electronic form
138       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
139       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
140       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
141       cal  and  Electronics  Engineers,  Inc  and  The  Open Group.  (This is
142       POSIX.1-2008 with the 2013 Technical Corrigendum  1  applied.)  In  the
143       event of any discrepancy between this version and the original IEEE and
144       The Open Group Standard, the original IEEE and The Open Group  Standard
145       is  the  referee document. The original Standard can be obtained online
146       at http://www.unix.org/online.html .
147
148       Any typographical or formatting errors that appear  in  this  page  are
149       most likely to have been introduced during the conversion of the source
150       files to man page format. To report such errors,  see  https://www.ker
151       nel.org/doc/man-pages/reporting_bugs.html .
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155IEEE/The Open Group                  2013                            TIMES(3P)
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