RFR: 8340733: Add scope for relaxing constraint on JavaCalls from CompilerThread [v3]

[Tomáš Zezula]

On Wed, 25 Sep 2024 06:05:15 GMT, Doug Simon <dnsimon at openjdk.org> wrote:

>> [JDK-8318694](https://bugs.openjdk.org/browse/JDK-8318694) limited the ability for JVMCI CompilerThreads to make Java upcalls. This is to mitigate against deadlock when an upcall does class loading. Class loading can easily create deadlock situations in `-Xcomp` or `-Xbatch` mode.
>> 
>> However, for Truffle, upcalls are unavoidable if Truffle partial evaluation occurs as part of JIT compilation inlining. This occurs when the Graal inliner sees a constant Truffle AST node which allows a Truffle-specific inlining extension to perform Truffle partial evaluation (PE) on the constant. Such PE involves upcalls to the Truffle runtime (running in Java).
>> 
>> This PR provides the escape hatch such that Truffle specific logic can put a compiler thread into "allow Java upcall" mode during the scope of the Truffle logic.
>
> Doug Simon has updated the pull request incrementally with one additional commit since the last revision:
> 
>   rename changeCompilerThreadCanCallJava to updateCompilerThreadCanCallJava

src/jdk.internal.vm.ci/share/classes/jdk/vm/ci/hotspot/CompilerThreadCanCallJavaScope.java line 81:

> 79: 
> 80:         if (vm != null) {
> 81:             vm.updateCompilerThreadCanCallJava(!state);

This is not correct.
The scope has to capture the original `_can_call_java` value in the constructor and restore it here in `close`.

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PR Review Comment: https://git.openjdk.org/jdk/pull/21171#discussion_r1776989493