RFR: 8284161: Implementation of Virtual Threads (Preview) [v3]

[Alan Bateman]

On Sat, 16 Apr 2022 11:05:47 GMT, Jaikiran Pai <jpai at openjdk.org> wrote:

>> 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?

Yes, this is intentional but it would be great to split out this change and get them into the main line in advance. There is a JEP size task required to re-visit all of the locking in java.io. In the case of the input/output streams, most of it is not documented and there are several inconsistencies. In the case of FilterInputStream, it doesn't use synchronization for the other ops.

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