Provide API to explicitly unmap MappedByteBuffer?

[Philippe Marschall]

Hi

Any serious user I know calls unmap directly. Either through the
Cleaner in Java 8 or through the new method on Unsafe in Java 9.

((sun.nio.ch.DirectBuffer) buffer).cleaner().clean()

Unsafe.theUnsafe.invokeCleaner(byteBuffer)

Cheers
Philippe

On Tue, Mar 20, 2018 at 11:39 AM, Langer, Christoph
<christoph.langer at sap.com> wrote:
> Hi,
>
>
>
> I was just handling a customer issue where Java code tried to delete a file
> on Windows which was mapped into memory vial FileChannel.map() before. It
> took me a little while to understand the issue but obviously the problem was
> that Windows still kept a delete lock on the file as long as the ByteBuffer
> was still mapped. This behavior is also documented cleanly:
> https://download.java.net/java/jdk10/docs/api/java/nio/MappedByteBuffer.html.
>
>
>
> So far so good, I just started wondering why there isn’t an API to force
> unmapping (cleanup) on a MappedByteBuffer? The app that opens the mapping
> simply reads a properties file at this place and I guess they should be able
> to change this place to use standard io easily and without observable
> performance problems. However, if they had a way to explicitly unmap the
> MappedByteBuffer it would also help.
>
>
>
> Was this topic already discussed? Is there a hard reason why explicit
> cleanup should not be offered? I guess people using MappedByteBuffers should
> know anyway what they are doing…
>
>
>
> Thanks & Best regards
>
> Christoph
>
>