RFR: 8129776: The optimized Stream returned from Files.lines should unmap the mapped byte buffer (if created) when closed [v2]

[Paul Sandoz]

On Tue, 26 Jan 2021 15:16:52 GMT, Roger Riggs <rriggs at openjdk.org> wrote:

>> Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   8129776: Remove brackets {} around single expression lambda
>
> Marked as reviewed by rriggs (Reviewer).

Looks good. There is some complexity because the `Spliterator` can be obtained from the `Stream` returned by `Files.lines()`. This is not a common case but unfortunately we need to deal with it, otherwise we could just unmap when the `Stream` is closed.  There are edge cases where by splits may occur but they are not traversed, but i don't think we should be concerned about. This is on a good best-effort basis to free up the resource.

Is unmapping via `nioAccess.unmapper(b).unmap();` wired up?

In `Buffer`:
                @Override
                public UnmapperProxy unmapper(ByteBuffer bb) {
                    if (bb instanceof MappedByteBuffer) {
                        return ((MappedByteBuffer)bb).unmapper();
                    } else {
                        return null;
                    }
                }

In MappedByteBuffer:
    UnmapperProxy unmapper() {
        return fd != null ?
                new UnmapperProxy() {
                    @Override
                    public long address() {
                        return address;
                    }

                    @Override
                    public FileDescriptor fileDescriptor() {
                        return fd;
                    }

                    @Override
                    public boolean isSync() {
                        return isSync;
                    }

                    @Override
                    public void unmap() {
                        throw new UnsupportedOperationException();
                    }
                } : null;
    }
I don't see where `unmapper` is overridden.

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PR: https://git.openjdk.java.net/jdk/pull/2229