On Wed, 4 Jun 2025 14:52:04 GMT, Johannes Bechberger <jbechber...@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.
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/25302#discussion_r2126817165
