RFR: JDK-8264111 (fs) Leaking NativeBuffers in case of errors during UnixUserDefinedFileAttributeView.read/write [v2]

[Alan Bateman]

On Thu, 25 Mar 2021 11:53:01 GMT, Sebastian Stenzel <github.com+1204330+overheadhunter at openjdk.org> wrote:

>> src/java.base/unix/classes/sun/nio/fs/UnixUserDefinedFileAttributeView.java line 174:
>> 
>>> 172:         if (dst instanceof sun.nio.ch.DirectBuffer buf) {
>>> 173:             long address = buf.address() + pos;
>>> 174:             int n = read(name, address, rem);
>> 
>> We need to add reachabilityFence here, don't mind if we do it now while changing this code or later.
>> That is, it should be try { n = read(name, address, rem); } finally { Reference.reachabilityFence(buf); }
>
> Never heard of this before, just read the docs the first time. Do I get this right, that this helps to protect against instant finalization of the buffer in e.g. `attrView.read("foo", ByteBuffer.allocateDirect(42))`?
> 
> What about the `write` case?

Yes, everywhere where the direct memory is accessed (so read and write here). I don't mind if we do it as a separate issue or here, I only suggested it here because it's changed the new code in this patch.

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PR: https://git.openjdk.java.net/jdk/pull/3171