On Thu, 10 Sep 2026 15:11:13 GMT, Jorn Vernee <[email protected]> wrote:
> Implement a method handle combinator that can be used to synchronize on an
> object monitor while executing a given target method handle.
>
> The returned method handle behaves similar to the notional code:
>
>
> R adapter(Object lock, A... a) throws Throwable {
> synchronized (lock) {
> return body.invokeExact(a...);
> }
> }
>
>
> The lambda form is similar to existing ones: we box up all the arguments for
> the body handle, call a fallback function which synchronizes and invokes the
> body with the boxed argument, then the `Object` result is fed to an unboxing
> handle to unbox the result if needed.
>
> There's a corresponding intrinsic in `InvokerBytecodeGenerator` which
> replaces these three operations with `monitorEnter`/`monitorExit`
> instructions, direct argument/return value forwarding without (un)boxing, and
> the necessary exception handling which makes sure we unlock the lock again in
> case the body throws an exception. The generated code is similar to what
> javac generates.
>
> ---------
> - [x] I confirm that I make this contribution in accordance with the [OpenJDK
> Interim AI Policy](https://openjdk.org/legal/ai).
Another remark: since what 90% of this LF is doing is to box and unbox
arguments, maybe we can later figure out a way to just attach an intrinsic to
the adapted MH for the interpreter `synchronize` so we don't need to spin the
LF but just need the InvokerBytecodeGenerator intrinsic.
-------------
PR Comment: https://git.openjdk.org/jdk/pull/32817#issuecomment-5651147804
