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

[Patricio Chilano Mateo]

On Wed, 4 Jun 2025 14:52:04 GMT, Johannes Bechberger <jbechberger at openjdk.org> wrote:

>> 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);
>   }

The `sigev_value` member is used to pass data that you can read in the signal handler. The address of `t` won't be valid anymore once you return from this function. In that example the address of `timerid ` is still valid.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2126817165