RFR: 8308745: ObjArrayKlass::allocate_objArray_klass may call into java while holding a lock [v2]

[Coleen Phillimore]

On Thu, 7 Mar 2024 00:54:30 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> OK.  It's a good thing HotSpot doesn't need to worry about priority-inheritance for mutexes.
>
> Semaphore seems simpler/cleaner and ready to use.

It's such a rare race and unusual condition that we could execute more Java code, that I started out with just a shared bit.  Then David suggested a semaphore that obeys the safepoint protocol, which seems a lot better.  I've literally skimmed over OSThreadWaitState.  It looks like Semaphore::wait_with_a_safepoint_check() uses it.  I still don't know why it exists:


// Note: the ThreadState is legacy code and is not correctly implemented.
// Uses of ThreadState need to be replaced by the state in the JavaThread.

enum ThreadState {


Does a PlatformMutex handle priority-inheritance? It still feels like it would be overkill for this usage.  I hope this RecursiveLocker does not become more widely used, where we would have to replace the simple implementation with something more difficult.  We should discourage further use when possible.

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PR Review Comment: https://git.openjdk.org/jdk/pull/17739#discussion_r1515364466