Integrated: 8257189: Handle concurrent updates of MH.form better

[Vladimir Ivanov]

On Thu, 26 Nov 2020 21:23:16 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

> Concurrent updates may lead to redundant LambdaForms created and unnecessary class loading when those are compiled. 
> 
> Most notably, it severely affects MethodHandle customization: when a MethodHandle is called from multiple threads, every thread starts customization which takes enough time for other threads to join, but only one of those customizations will be picked.
> 
> Coordination between threads requesting the updates and letting a single thread proceed avoids the aforementioned problem. Moreover, there's no need to wait until the update in-flight is over: all other threads (except the one performing the update) can just proceed with the invocation using the existing MH.form. 
> 
> Testing:
> - manually monitored the behavior on a stress test from [JDK-8252049](https://bugs.openjdk.java.net/browse/JDK-8252049)
> - tier1-4

This pull request has now been integrated.

Changeset: 692b273e
Author:    Vladimir Ivanov <vlivanov at openjdk.org>
URL:       https://git.openjdk.java.net/jdk/commit/692b273e
Stats:     89 lines in 5 files changed: 36 ins; 20 del; 33 mod

8257189: Handle concurrent updates of MH.form better

Reviewed-by: redestad, psandoz

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PR: https://git.openjdk.java.net/jdk/pull/1472