RFR: 8256383: PlatformMutex::try_lock has different semantics on Windows and Posix

[Stefan Karlsson]

On Tue, 17 Nov 2020 05:41:44 GMT, David Holmes <dholmes at openjdk.org> wrote:

> Mutex::try_lock has to allow for the possibility that the PlatformMutex::try_lock allows recursive locking.
> 
> Added additional commentary on the semantics provided by Mutex and the PlatformMutex classes.
> 
> Testing: GHA, mach5 tiers 1-3

@dholmes-ora It makes difference w.r.t. atomicity. You can argue that this isn't important in this specific use-case, but I thought there was an agreement among HotSpot devs to use Atomic::load for racy access. Esp. now that we've moved to C++11 and racy loads are considered undefined behavior. John created JDK-8234192 when this was discussed earlier.

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PR: https://git.openjdk.java.net/jdk/pull/1247