RFR: 8140241: (fc) Data transfer from FileChannel to itself causes hang in case of overlap [v4]

[Alan Bateman]

On Wed, 11 Aug 2021 15:49:55 GMT, Brian Burkhalter <bpb at openjdk.org> wrote:

>> This request proposes to fix a failure on macOS which occurs when transferring to or from a file channel from or to the same file channel when the source and destination intervals overlap.
>
> Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:
> 
>   8140241: Restructure test to use try-with-resources for file closing

Marked as reviewed by alanb (Reviewer).

src/java.base/share/classes/sun/nio/ch/FileChannelImpl.java line 591:

> 589:             synchronized (positionLock) {
> 590:                 long posThis = position();
> 591:                 if (posThis - count + 1 <= position &&

I realise I suggested we need the positionLock here but I don't think it is needed now because there is only one call to position().

src/java.base/share/classes/sun/nio/ch/FileChannelImpl.java line 803:

> 801: 
> 802:         if (src instanceof FileChannelImpl) {
> 803:             long n = transferFromFileChannel((FileChannelImpl)src, position, count);

It might be a bit cleaner to use the pattern matching with the instanceof to avoid the cast to FileChannelImpl.

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PR: https://git.openjdk.java.net/jdk/pull/5061