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).
Comment nits:
src/java.base/share/classes/java/lang/invoke/InvokerBytecodeGenerator.java line
1188:
> 1186: Class<?> returnType =
> result.function.resolvedHandle().type().returnType();
> 1187: MethodType bodyType = args.function.resolvedHandle().type()
> 1188: .dropParameterTypes(0, 1) // drop collector
Suggestion:
.dropParameterTypes(0, 1) // drop lock
src/java.base/share/classes/java/lang/invoke/InvokerBytecodeGenerator.java line
1203:
> 1201: cob.monitorenter();
> 1202: emitPushArgument(cob, invoker, 1); // push body handle
> 1203: emitPushArguments(cob, args, 1); // push args, skip collector
Suggestion:
emitPushArguments(cob, args, 1); // push args, skip lock
-------------
PR Review: https://git.openjdk.org/jdk/pull/32817#pullrequestreview-5172334190
PR Review Comment: https://git.openjdk.org/jdk/pull/32817#discussion_r3983549807
PR Review Comment: https://git.openjdk.org/jdk/pull/32817#discussion_r3983550846
