[jdk16] RFR: 8259027: NullPointerException in makeMappedSegment due to NULL Unmapper when length of segment is 0 [v2]

Uwe Schindler uschindler at openjdk.java.net
Tue Jan 5 15:53:56 UTC 2021

On Tue, 5 Jan 2021 15:42:11 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> When the size of the memory map is zero, FileChannelImpl returns a `null` Unmapper - this creates issues to the mapped memory segment implementation.
>> To fix, I've created an empty mapped segment class which is initialized to sensible defaults, and whose implenentation of force/load etc. do nothing.
>> We already had a test for this condition - but the test was missing the `@Test` annotation, so it was not run! I've now beefed up the test a bit to make sure that mapped segment operations do not throw.
> Maurizio Cimadamore has updated the pull request incrementally with one additional commit since the last revision:
>   Added empty mapping support for different access modes

Looks fine!
In fact it's more complicated than the workaround, but this allows to call load() or force().


Marked as reviewed by uschindler (Author).

PR: https://git.openjdk.java.net/jdk16/pull/83

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