RFR: 8297286: runtime/vthread tests crashing after JDK-8296324 [v13]

[Serguei Spitsyn]

On Thu, 30 Mar 2023 19:00:03 GMT, Patricio Chilano Mateo <pchilanomate at openjdk.org> wrote:

>> Serguei Spitsyn has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   review: tweak in count_transitions_and_correct_jvmti_thread_states
>
> test/hotspot/jtreg/serviceability/jvmti/vthread/ToggleNotifyJvmtiTest/ToggleNotifyJvmtiTest.java line 129:
> 
>> 127:     }
>> 128: 
>> 129:     static synchronized private void startThreads() {
> 
> So making this method synchronized instead of startThread() will make it less likely that we will face the previous issue, but it is still timing dependent, because the call to start the launcher can return before the launcher reaches here. It will be very unlikely given the sleeps but if we want to guard against any surprises we could have a variable set in startThreads() and in finishThreads() we check and wait until that variable is set.

Thank you for the concern.
The `startThread()` below which is called from `startThreads()` has the call to `thread.ensureReady()` which waits until the target tested thread really starts and sets the `threadReady` field. So, there is no race condition as the `startThreads()` and `finishThreads()` are synchronized methods.


    static private void startThread(int i) {
        String name = "TestedThread" + i;
        TestedThread thread = new TestedThread(name);
        vts[i] = Thread.ofVirtual().name(name).start(thread);
        thread.ensureReady();
        threads[i] = thread;
        log("# Java: started vthread: " + name);
    }

    static synchronized private void startThreads() {
        log("\n# Java: Starting vthreads");
        for (int i = 0; i < VTHREADS_CNT; i++) {
            sleep(1);
            startThread(i);
        }
    }

    static private synchronized void finishThreads() {
        try {
            for (int i = 0; i < VTHREADS_CNT; i++) {
                TestedThread thread = threads[i];
                thread.letFinish();
                vts[i].join();
            }
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
    }

Please, let me know if I'm missing anything.

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PR Review Comment: https://git.openjdk.org/jdk/pull/13133#discussion_r1153820099