RFR: 8358537: (bf) JavaNioAccess::getBufferAddress bypasses direct buffer MemorySession state check

[Brian Burkhalter]

On Tue, 3 Jun 2025 23:57:21 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

>> I thin it's running into this method in DirectBufferX:
>> 
>>     public long address() {
>>         MemorySessionImpl session = session();
>>         if (session != null) {
>>             if (session.ownerThread() == null && session.isCloseable()) {
>>                 throw new UnsupportedOperationException("ByteBuffer derived from closeable shared sessions not supported");
>>             }
>
> Oh, I see. IIRC this is why the shared secrets are bypassing the `address()` method. For shared arenas the caller is supposed to do an acquire/release, and then use shared secrets to get the buffer address, bypassing this check.
> 
> @minborg recently did some work to change over uses of `DirectBuffer::address` in https://github.com/openjdk/jdk/pull/25324 and https://github.com/openjdk/jdk/pull/25321
> 
> If ByteBuffers derived from segments with shared arenas no longer work with this patch, that seems like a regression to me.

It could be. More study is clearly needed. This is related to #25531.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25631#discussion_r2125195256