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

[Johannes Bechberger]

On Wed, 4 Jun 2025 14:54:44 GMT, Patricio Chilano Mateo <pchilanomate at openjdk.org> wrote:

>> 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.

Why is this a problem? We don't leak `&t` outside of `create_timer_for_thread`.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2126820560