On Wed, 3 Apr 2024 10:04:36 GMT, Alan Bateman <al...@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, if there is preemption
> when attempting to compensate, or potentially forced preemption in the
> future. 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 the loom repo for several months.
src/java.base/share/classes/java/lang/System.java line 2262:
> 2260: @Override
> 2261: public long transferTo(OutputStream out) throws IOException {
> 2262: boolean attempted = Blocker.begin();
Hello Alan, why do we mark transferTo as potentially blocking operation which
might need compensation? As far as I can see in the underlying implementation
of `FileInputStream.transferTo()` it either calls the
`FileChannel.transferTo()` or does a `in.read()` followed by `out.write()`. In
either of those cases wouldn't the underlying `InputStream/OutputStream`
already have the necessary `Blocker` calls?
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PR Review Comment: https://git.openjdk.org/jdk/pull/18598#discussion_r1557679570
