Integrated: 8329593: Drop adjustments to target parallelism when virtual threads do I/O on files opened for buffered I/O

[Alan Bateman]

On Wed, 3 Apr 2024 10:04:36 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.

This pull request has now been integrated.

Changeset: 412e306d
Author:    Alan Bateman <alanb at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/412e306d81209c05f55aee7663f7abb80286e361
Stats:     1084 lines in 28 files changed: 215 ins; 624 del; 245 mod

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

Reviewed-by: bpb, jpai

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PR: https://git.openjdk.org/jdk/pull/18598