On Thu, 15 Aug 2024 11:20:23 GMT, Markus Grönlund <[email protected]> wrote:
>> Greetings,
>>
>> Explicitly pin a virtual thread before acquiring the JFR string pool monitor
>> because migrating a carrier thread local event writer object onto another
>> carrier thread is impossible.
>>
>> During event commit, the thread is in a critical section because it has
>> loaded a carrier thread local event writer object. For virtual threads, a
>> contended monitor, such as a synchronized block, is a point where a thread
>> could become unmounted.
>>
>> A monitor guards the JFR string pool, but remounting a virtual thread onto
>> another carrier is impossible because of the event writer.
>>
>> Therefore, it's imperative to use explicit pin constructs to prevent
>> unmounting at this location.
>>
>> Testing: jdk_jfr
>>
>> Thanks
>> Markus
>
> Markus Grönlund has updated the pull request incrementally with one
> additional commit since the last revision:
>
> update test comment
Functionally seems fine. Could be optimised a bit.
src/jdk.jfr/share/classes/jdk/jfr/internal/StringPool.java line 86:
> 84:
> 85: private static void unpinVirtualThread() {
> 86: if (Thread.currentThread().isVirtual() &&
> ContinuationSupport.isSupported()) {
If you are at all concerned about overhead here then pin could return a boolean
to indicate if the pin happened and oyu could then unpin just by checking that
boolean and avoid doing the isVirtual and isSupported checks again.
-------------
Marked as reviewed by dholmes (Reviewer).
PR Review: https://git.openjdk.org/jdk/pull/20588#pullrequestreview-2240268782
PR Review Comment: https://git.openjdk.org/jdk/pull/20588#discussion_r1718332618
