RFR: 8296472: Remove ObjectLocker around appendToClassPathForInstrumentation call [v3]

[Coleen Phillimore]

On Mon, 7 Nov 2022 20:40:33 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> This patch moves the acquisition of the boot class loader lock out of the JVM and into the Java function.
>> Tested with tier1-4, and jvmti and jdi tests locally.
>
> Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:
> 
>   really revert the file

We call compute_java_loaders with upcall to ClassLoader.getSystemClassLoader() after initPhase3 but before JVMTI live phase:

https://github.com/coleenp/jdk/blob/master/src/hotspot/share/runtime/threads.cpp#L731

which is when jvmti calls this:
https://github.com/coleenp/jdk/blob/master/src/hotspot/share/prims/jvmtiEnv.cpp#L703

Can one create a class loader to override this function, and does one expect the JVM to synchronize it on the system class loader object (returned by getSystemClassLoader)?  This feels too remote to try to explain in a CSR.

I'll look to see if we have tests for this case.

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PR: https://git.openjdk.org/jdk/pull/11023