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

[Brian Burkhalter]

On Tue, 10 Aug 2021 01:21:21 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.

Fixed the overlap checks and the transferFrom n == 0 case. The scenario is unlikely but if it occurs the consequences are serious. I am trying to find out about the Apple bug (actually 2586576 as the one I filed, 37764443, was marked a duplicate).

As an aside, I think that the cast to `int` at line 689 of `FileChannelImpl` should have been removed in the fix for [JDK-8271308](https://bugs.openjdk.java.net/browse/JDK-8271308) but was not.

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