RFR: 8329593: Drop adjustments to target parallelism when virtual threads do I/O on files opened for buffered I/O [v2]

[Brian Burkhalter]

On Mon, 22 Apr 2024 12:45:53 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>> This change drops the adjustments to the virtual thread scheduler's target parallelism when virtual threads do file operations on files that are opened for buffered I/O. These operations are usually just too short to have any benefit and may have a negative benefit when reading/writing a small number of bytes. There is no change for read/write operations on files opened for direct I/O or when writing to files that are opened with options for synchronized I/O file integrity (O_SYNC/O_DSYNC and equivalents). Sergery Kuksenko is polishing benchmarks that includes this area, this is for a future PR.
>> 
>> In addition, the blocker mechanism is updated to handle reentrancy (as can happen if debugging code is added to ForkJoinPool) and preemption when compensating (as can happen when substituting a heap buffer with a direct buffer in some I/O operations).  This part is a pre-requisite to the changes to better support object monitor there are more places where preemption is possible and this quickly leads to unbalanced begin/end.
>> 
>> The changes have been baking in loom repo for some time.
>
> Alan Bateman has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:
> 
>  - Merge
>  - Sync up from loom repo, update copyright headers
>  - Merge
>  - Merge
>  - Initial commit

Looks fine. I think dropping the `transferTo` overloads for now is good.

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Marked as reviewed by bpb (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/18598#pullrequestreview-2015549163