man3/pthread_getcpuclockid.3

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  26 .TH PTHREAD_GETCPUCLOCKID 3 2019-03-06 "Linux" "Linux Programmer's Manual"
  27 .SH NAME
  28 pthread_getcpuclockid \- retrieve ID of a thread's CPU time clock
  29 .SH SYNOPSIS
  30 .nf
  31 .B #include <pthread.h>
  32 .B #include <time.h>
  33 .PP
  34 .BI "int pthread_getcpuclockid(pthread_t " thread ", clockid_t *" clockid );
  35 .PP
  36 Compile and link with \fI\-pthread\fP.
  37 .fi
  38 .SH DESCRIPTION
  39 The
  40 .BR pthread_getcpuclockid ()
  41 function obtains the ID of the CPU-time clock of the thread whose ID is
  42 given in
  43 .IR thread ,
  44 and returns it in the location pointed to by
  45 .IR clockid .
  46 .\" The clockid is constructed as follows:
  47 .\" *clockid = CLOCK_THREAD_CPUTIME_ID | (pd->tid << CLOCK_IDFIELD_SIZE)
  48 .\" where CLOCK_IDFIELD_SIZE is 3.
  49 .SH RETURN VALUE
  50 On success, this function returns 0;
  51 on error, it returns a nonzero error number.
  52 .SH ERRORS
  53 .TP
  54 .B ENOENT
  55 .\" CLOCK_THREAD_CPUTIME_ID not defined
  56 Per-thread CPU time clocks are not supported by the system.
  57 .\"
  58 .\" Looking at nptl/pthread_getcpuclockid.c an ERANGE error would
  59 .\" be possible if kernel thread IDs took more than 29 bits (which
  60 .\" they currently cannot).
  61 .TP
  62 .B ESRCH
  63 No thread with the ID
  64 .I thread
  65 could be found.
  66 .SH VERSIONS
  67 This function is available in glibc since version 2.2.
  68 .SH ATTRIBUTES
  69 For an explanation of the terms used in this section, see
  70 .BR attributes (7).
  71 .TS
  72 allbox;
  73 lbw23 lb lb
  74 l l l.
  75 Interface       Attribute       Value
  76 T{
  77 .BR pthread_getcpuclockid ()
  78 T}      Thread safety   MT-Safe
  79 .TE
  80 .SH CONFORMING TO
  81 POSIX.1-2001, POSIX.1-2008.
  82 .SH NOTES
  83 When
  84 .I thread
  85 refers to the calling thread,
  86 this function returns an identifier that refers to the same clock
  87 manipulated by
  88 .BR clock_gettime (2)
  89 and
  90 .BR clock_settime (2)
  91 when given the clock ID
  92 .BR CLOCK_THREAD_CPUTIME_ID .
  93 .SH EXAMPLE
  94 The program below creates a thread and then uses
  95 .BR clock_gettime (2)
  96 to retrieve the total process CPU time,
  97 and the per-thread CPU time consumed by the two threads.
  98 The following shell session shows an example run:
  99 .PP
 100 .in +4n
 101 .EX
 102 $ \fB./a.out\fP
 103 Main thread sleeping
 104 Subthread starting infinite loop
 105 Main thread consuming some CPU time...
 106 Process total CPU time:    1.368
 107 Main thread CPU time:      0.376
 108 Subthread CPU time:        0.992
 109 .EE
 110 .in
 111 .SS Program source
 112 \&
 113 .EX
 114 /* Link with "\-lrt" */
 115
 116 #include <time.h>
 117 #include <stdio.h>
 118 #include <stdlib.h>
 119 #include <unistd.h>
 120 #include <pthread.h>
 121 #include <string.h>
 122 #include <errno.h>
 123
 124 #define handle_error(msg) \e
 125         do { perror(msg); exit(EXIT_FAILURE); } while (0)
 126
 127 #define handle_error_en(en, msg) \e
 128         do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)
 129
 130 static void *
 131 thread_start(void *arg)
 132 {
 133     printf("Subthread starting infinite loop\en");
 134     for (;;)
 135         continue;
 136 }
 137
 138 static void
 139 pclock(char *msg, clockid_t cid)
 140 {
 141     struct timespec ts;
 142
 143     printf("%s", msg);
 144     if (clock_gettime(cid, &ts) == \-1)
 145         handle_error("clock_gettime");
 146     printf("%4ld.%03ld\en", ts.tv_sec, ts.tv_nsec / 1000000);
 147 }
 148
 149 int
 150 main(int argc, char *argv[])
 151 {
 152     pthread_t thread;
 153     clockid_t cid;
 154     int j, s;
 155
 156     s = pthread_create(&thread, NULL, thread_start, NULL);
 157     if (s != 0)
 158         handle_error_en(s, "pthread_create");
 159
 160     printf("Main thread sleeping\en");
 161     sleep(1);
 162
 163     printf("Main thread consuming some CPU time...\en");
 164     for (j = 0; j < 2000000; j++)
 165         getppid();
 166
 167     pclock("Process total CPU time: ", CLOCK_PROCESS_CPUTIME_ID);
 168
 169     s = pthread_getcpuclockid(pthread_self(), &cid);
 170     if (s != 0)
 171         handle_error_en(s, "pthread_getcpuclockid");
 172     pclock("Main thread CPU time:   ", cid);
 173
 174     /* The preceding 4 lines of code could have been replaced by:
 175        pclock("Main thread CPU time:   ", CLOCK_THREAD_CPUTIME_ID); */
 176
 177     s = pthread_getcpuclockid(thread, &cid);
 178     if (s != 0)
 179         handle_error_en(s, "pthread_getcpuclockid");
 180     pclock("Subthread CPU time: 1    ", cid);
 181
 182     exit(EXIT_SUCCESS);         /* Terminates both threads */
 183 }
 184 .EE
 185 .SH SEE ALSO
 186 .BR clock_gettime (2),
 187 .BR clock_settime (2),
 188 .BR timer_create (2),
 189 .BR clock_getcpuclockid (3),
 190 .BR pthread_self (3),
 191 .BR pthreads (7),
 192 .BR time (7)