On Fri, 15 Nov 2024 20:54:56 GMT, Aleksey Shipilev <sh...@openjdk.org> wrote:

> DirectByteBuffers are still using old `jdk.internal.ref.Cleaner` 
> implementation. That implementation carries a doubly-linked list, and so 
> makes DBB suffer from the same issue fixed for generic 
> `java.lang.ref.Cleaner` users with 
> [JDK-8343704](https://bugs.openjdk.org/browse/JDK-8343704). See the bug for 
> the reproducer.
> 
> We can migrate DBBs to use `java.lang.ref.Cleaner`.
> 
> There are two pecularities during this rewrite.
> 
> First, the old ad-hoc `Cleaner` implementation used to exit the VM when 
> cleaning action failed. I presume it was to avoid memory leak / accidental 
> reuse of the buffer. I moved the relevant block to `Deallocator` directly. 
> Unfortunately, I cannot easily test it.
> 
> Second is quite a bit hairy. Old DBB cleaning code was hooked straight into 
> `Reference` processing loop. This was possible because we could infer that 
> the weak references we are processing were DBB cleaning actions, since old 
> `Cleaner` was the only use of this code. With standard `Cleaner`, we have 
> lost this association, and so we cannot really do this from the reference 
> processing loop. With the patched version, we now rely on normal `Cleaner` 
> thread to do cleanups for us.
> 
> Because of this, there is a new outpacing opportunity window where reference 
> processing might have been over, but cleaner thread has not reacted yet. This 
> is why we need another way to check progress that involves checking if 
> cleaner has acted.
> 
> Additional testing:
>  - [x] Linux x86_64 server fastdebug, `java/nio java/io`
>  - [x] Linux AArch64 server fastdebug, `java/nio java/io`
>  - [x] Linux x86_64 server fastdebug, `all`
>  - [x] Linux AArch64 server fastdebug, `all`

This pull request has been closed without being integrated.

-------------

PR: https://git.openjdk.org/jdk/pull/22165

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