RFR: 8357847: (ch) AsynchronousFileChannel implementations should support FFM Buffers [v4]

[Alan Bateman]

On Thu, 5 Jun 2025 17:48:48 GMT, Brian Burkhalter <bpb at openjdk.org> wrote:

>> Acquire the scope of a direct buffer before it is used and release it after the task has finished with it, whether the task execution is immediate or pended.
>
> Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:
> 
>   8357912: Add reading to test of unsupported views

src/java.base/share/classes/sun/nio/ch/SimpleAsynchronousFileChannelImpl.java line 393:

> 391:         if (src.isDirect()) {
> 392:             IOUtil.acquireScope(src, true);
> 393:             ((DirectBuffer)src).address();

Is the using of address() here for testing purposes?

test/jdk/java/nio/channels/AsynchronousFileChannel/Basic.java line 632:

> 630:         rand.nextBytes(buf);
> 631:         Arena arena = isConfined ? Arena.ofConfined() : Arena.ofShared();
> 632:         return arena.allocate(buf.length).asByteBuffer().put(buf).flip();

For the asynchronous channels then we should only prohibit thread-confined, using a buffer that is a view of a memory segment allocated from a shared arena is okay.  I've included (disabled-for-now) test in draft changes for JDK-8358958 to test attempting to close a shared arena while a write op is outstanding, I think we can use that to test the changes here.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25531#discussion_r2135636952
PR Review Comment: https://git.openjdk.org/jdk/pull/25531#discussion_r2135634762