RFR: 4833719: (bf) Views of MappedByteBuffers are not MappedByteBuffers, and cannot be forced [v4]

[Andrew Dinn]

On Mon, 15 Mar 2021 21:27:25 GMT, Brian Burkhalter <bpb at openjdk.org> wrote:

>> Please consider this proposal to add covariant overrides to `MappedByteBuffer` for the methods `compact()`, `duplicate()`, `slice()`, and `slice(int,int)`.
>> 
>> The methods in question are added as abstract specifications in `MappedByteBuffer` and their implementations in `Direct-X-Buffer.java.template`. In `MappedByteBuffer` the `isSync()` method is changed to have package access, and a final package scope method `FileDescriptor fileDescriptor()` is added to return the associated file descriptor. Specification verbiage is added to the new covariant overrides, and the specification of `force()` is enhanced slightly. (The `unmapper()` method offers an alternative way to obtain the file descriptor and sync mode without the need for package access `fileDescriptor()` and `isSync()` methods.)
>> 
>> In `Direct-X-Buffer.java.template` the constructor for duplicates and slices is modified to accept parameters for the file descriptor and sync mode for byte buffers. The uses of this constructor are correspondingly modified.
>> 
>> A test is added to exercise the new methods. Verifying that `force()` is actually doing anything is not verified by this test but was checked manually. The change passes all other existing tests in tiers 1-3.
>> 
>> Other methods for which it might be worth adding covariant overrides are the `get()` and `put()` methods which return a buffer, and, less interesting, the `put$Type$()` methods.
>
> Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:
> 
>   4833719: Corrected faux pas in correcting faux pas

src/java.base/share/classes/java/nio/MappedByteBuffer.java line 377:

> 375:      * {@code force()} on the returned buffer, will only act on the sub-range
> 376:      * of this buffer that the returned buffer represents, namely
> 377:      * {@code [position(),limit()]}.

Is the closing bracket on this interval meant to be ']' or ')'? i.e. is the interval inclusive of exclusive of the value at the index returned by limit()?

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PR: https://git.openjdk.java.net/jdk/pull/2902