RFR: 8342818: Implement JEP 509: JFR CPU-Time Profiling [v50]

[Johannes Bechberger]

On Wed, 4 Jun 2025 14:46:27 GMT, Johannes Bechberger <jbechberger at openjdk.org> wrote:

>> Sorry where does it say that? I think you are looking at the example in that page which makes use of sival_ptr in the signal handler. In that example reading from that timer address in the handler is valid but for us we would be accessing invalid memory. Plus we are not really reading it.
>
> Why would we be accessing invalid memory?

Which differences to the example code are you seeing?


 sev.sigev_notify = SIGEV_SIGNAL;
           sev.sigev_signo = SIG;
           sev.sigev_value.sival_ptr = &timerid;
           if (timer_create(CLOCKID, &sev, &timerid) == -1)
               errExit("timer_create");

           printf("timer ID is %#jx\n", (uintmax_t) timerid);

           /* Start the timer. */

           freq_nanosecs = atoll(argv[2]);
           its.it_value.tv_sec = freq_nanosecs / 1000000000;
           its.it_value.tv_nsec = freq_nanosecs % 1000000000;
           its.it_interval.tv_sec = its.it_value.tv_sec;
           its.it_interval.tv_nsec = its.it_value.tv_nsec;



Is similar to:


 ((int*)&sev.sigev_notify)[1] = thread->osthread()->thread_id();
  clockid_t clock;
  int err = pthread_getcpuclockid(thread->osthread()->pthread_id(), &clock);
  if (err != 0) {
    log_error(jfr)("Failed to get clock for thread sampling: %s", os::strerror(err));
    return false;
  }
  if (timer_create(clock, &sev, &t) < 0) {
    return false;
  }
  int64_t period = get_sampling_period();
  if (period != 0) {
    set_timer_time(t, period);
  }

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PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2126810984