RFR: 8233281: Obsolete UseSemaphoreGCThreadsSynchronization

[Kim Barrett]

> On Aug 14, 2020, at 9:42 AM, Stefan Karlsson <stefan.karlsson at oracle.com> wrote:
> 
> Hi all,
> 
> Please review this patch to obsolete the diagnostic UseSemaphoreGCThreadsSynchronization JVM option.
> 
> https://bugs.openjdk.java.net/browse/JDK-8233281
> https://cr.openjdk.java.net/~stefank/8233281/webrev.01
> 
> I added this flag when implementing:
> 8087324: Use semaphores when starting and stopping GC task threads
> 
> It was intended to be a fallback solution if the new semaphore implementation failed to to work for any reason. We've used the semaphore code for many years now, and the Mutex implementation has bit rottened.
> 
> The proposed patch both obsoletes the the JVM flag, and removes the Mutex dispatch mechanism.
> 
> Thanks,
> StefanK

Looks good, so far as it goes.

Is there a reason to retain the distinction between GangTaskDispatcher and SemaphoreGangTaskDispatcher?
If not, I’m okay with separating the hierarchy collapse as a cleanup to follow.