On Sun, 13 Sep 2026 04:10:10 GMT, Chen Liang <[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).
>
> src/java.base/share/classes/java/lang/invoke/MethodHandleImpl.java line 2326:
>
>> 2324: }
>> 2325:
>> 2326: lform = LambdaForm.create(basicType.parameterCount() + 1,
>> names, Kind.SYNCHRONIZE);
>
> Side remark: we should really replace all `basicType.parameterCount() + 1`
> with `ARG_LIMIT`.
Good idea. Looks like a safe change to make as well. I could do it in this
patch if you want.
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PR Review Comment: https://git.openjdk.org/jdk/pull/32817#discussion_r4004401978
