On Fri, 15 Apr 2022 11:45:01 GMT, Alan Bateman <al...@openjdk.org> wrote:

>> This is the implementation of JEP 425: Virtual Threads (Preview); TBD which 
>> JDK version to target.
>> 
>> We will refresh this PR periodically to pick up changes and fixes from the 
>> loom repo.
>> 
>> Most of the new mechanisms in the HotSpot VM are disabled by default and 
>> require running with `--enable-preview` to enable.
>> 
>> The patch has support for x64 and aarch64 on the usual operating systems 
>> (Linux, macOS, and Windows). There are stubs (calling Unimplemented) for 
>> zero and some of the other ports. Additional ports can be contributed via 
>> PRs against the fibers branch in the loom repo.
>> 
>> There are changes in many areas. To reduce notifications/mails, the labels 
>> have been trimmed down for now to hotspot, serviceability and core-libs. 
>> We'll add the complete set of labels when the PR is further along.
>> 
>> The changes include a refresh of java.util.concurrent and ForkJoinPool from 
>> Doug Lea's CVS. These changes will probably be proposed and integrated in 
>> advance of this PR.
>> 
>> The changes include some non-exposed and low-level infrastructure to support 
>> the (in draft) JEPs for Structured Concurrency and Scope Locals. This is to 
>> make life a bit easier and avoid having to separate VM changes and juggle 
>> branches at this 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:
> 
>  - Refresh
>  - Refresh
>  - Merge with jdk-19+18
>  - Refresh
>  - Initial push

src/java.base/share/classes/java/io/FilterInputStream.java line 233:

> 231:      */
> 232:     @Override
> 233:     public void reset() throws IOException {

I suspect this change to remove synchronization from `mark()` and `reset()` is 
intentional. The `FilterInputStream` class doesn't explain the thread safety 
semantics, nor can I find commit history which would hint on why these (and 
only these) methods were syncrhonized. But it looks like this synchronization 
was there to serialize calls to `mark()` and `reset()` on the same 
`FilterInputStream` from multiple threads. With this synchronization now 
removed, subclasses or even direct usages of `FilterInputStream` would now be 
impacted. Potentially outside of the JDK. Would that be a concern?

-------------

PR: https://git.openjdk.java.net/jdk/pull/8166

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