1 .\" Copyright (c) 2009 Linux Foundation, written by Michael Kerrisk
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26 .TH PTHREAD_GETCPUCLOCKID 3 2021-03-22 "Linux" "Linux Programmer's Manual"
28 pthread_getcpuclockid \- retrieve ID of a thread's CPU time clock
31 .B #include <pthread.h>
34 .BI "int pthread_getcpuclockid(pthread_t " thread ", clockid_t *" clockid );
36 Compile and link with \fI\-pthread\fP.
40 .BR pthread_getcpuclockid ()
41 function obtains the ID of the CPU-time clock of the thread whose ID is
44 and returns it in the location pointed to by
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.
50 On success, this function returns 0;
51 on error, it returns a nonzero error number.
55 .\" CLOCK_THREAD_CPUTIME_ID not defined
56 Per-thread CPU time clocks are not supported by the system.
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).
67 This function is available in glibc since version 2.2.
69 For an explanation of the terms used in this section, see
77 Interface Attribute Value
79 .BR pthread_getcpuclockid ()
80 T} Thread safety MT-Safe
86 POSIX.1-2001, POSIX.1-2008.
90 refers to the calling thread,
91 this function returns an identifier that refers to the same clock
96 when given the clock ID
97 .BR CLOCK_THREAD_CPUTIME_ID .
99 The program below creates a thread and then uses
100 .BR clock_gettime (2)
101 to retrieve the total process CPU time,
102 and the per-thread CPU time consumed by the two threads.
103 The following shell session shows an example run:
109 Subthread starting infinite loop
110 Main thread consuming some CPU time...
111 Process total CPU time: 1.368
112 Main thread CPU time: 0.376
113 Subthread CPU time: 0.992
119 /* Link with "\-lrt" */
130 #define handle_error(msg) \e
131 do { perror(msg); exit(EXIT_FAILURE); } while (0)
133 #define handle_error_en(en, msg) \e
134 do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)
137 thread_start(void *arg)
139 printf("Subthread starting infinite loop\en");
145 pclock(char *msg, clockid_t cid)
150 if (clock_gettime(cid, &ts) == \-1)
151 handle_error("clock_gettime");
152 printf("%4jd.%03ld\en", (intmax_t) ts.tv_sec, ts.tv_nsec / 1000000);
156 main(int argc, char *argv[])
162 s = pthread_create(&thread, NULL, thread_start, NULL);
164 handle_error_en(s, "pthread_create");
166 printf("Main thread sleeping\en");
169 printf("Main thread consuming some CPU time...\en");
170 for (int j = 0; j < 2000000; j++)
173 pclock("Process total CPU time: ", CLOCK_PROCESS_CPUTIME_ID);
175 s = pthread_getcpuclockid(pthread_self(), &cid);
177 handle_error_en(s, "pthread_getcpuclockid");
178 pclock("Main thread CPU time: ", cid);
180 /* The preceding 4 lines of code could have been replaced by:
181 pclock("Main thread CPU time: ", CLOCK_THREAD_CPUTIME_ID); */
183 s = pthread_getcpuclockid(thread, &cid);
185 handle_error_en(s, "pthread_getcpuclockid");
186 pclock("Subthread CPU time: 1 ", cid);
188 exit(EXIT_SUCCESS); /* Terminates both threads */
192 .BR clock_gettime (2),
193 .BR clock_settime (2),
194 .BR timer_create (2),
195 .BR clock_getcpuclockid (3),
196 .BR pthread_self (3),