RFR: 8319801: Recursive lightweight locking: aarch64 implementation

[Andrew Haley]

On Fri, 10 Nov 2023 13:00:52 GMT, Axel Boldt-Christmas <aboldtch at openjdk.org> wrote:

> The aarch64 C2 port tries to avoid stronger memory semantics where ever possible. In C2 lock it first does a relaxed load of the mark word to check for inflation. Both lock and unlock uses a load/store exclusive register pair to transition the mark word.

It's probably not a good idea to use load/store exclusive, because recent AArch64 implementations scale very badly under contention. Better to use atomic update instructions.

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PR Comment: https://git.openjdk.org/jdk/pull/16608#issuecomment-1805737519