RFR: 8340830: Console.readLine() and Console.printf() are mutually blocking [v6]

[Naoto Sato]

On Tue, 3 Feb 2026 18:55:29 GMT, Justin Lu <jlu at openjdk.org> wrote:

>> Naoto Sato 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 nine additional commits since the last revision:
>> 
>>  - Reflects Jai's review comments
>>  - Merge branch 'master' into JDK-8340830-Console-readLine-printf-mutually-blocking
>>  - Added @requires condition
>>  - added jline test run
>>  - Merge branch 'master' into JDK-8340830-Console-readLine-printf-mutually-blocking
>>  - Fixed indentation
>>  - Made ProxyingConsole value-based, used anonymous class for LazyConstant
>>  - Refine exceptions
>>  - initial commit
>
> test/jdk/java/io/Console/ReadWriteBlockingTest.java line 78:
> 
>> 76:         CountDownLatch latch = new CountDownLatch(2);
>> 77: 
>> 78:         Thread.ofVirtual().start(() -> {
> 
> Based on the way this test is setup with _expect_, I think the previous testing code was actually better at detecting the issue at hand, since it "presumably" had a higher chance to `readLine` first. Given the old implementation, `readLine` would acquire the write lock unnecessarily, preventing `printf` from entering and executing, causing the test to fail since _expect_ would never receive the "printf() invoked" and never be able to provide input to `readLine`.
> 
> The new test "presumably" has equal chances to either read or write first. However, if the `printf` executes first, I don't see how the test will fail. With the old implementation, even if `printf` acquires the lock at first and `readLine` was blocked from entering, `printf` will eventually finish and release the lock, and provide the expected message to _expect_.

Actually, I think the test is deterministic, even withouth any sleep/latch. The reason is that the wait is released with `expect` when it receives "printf() invoked" no matter which threads uses the console first. Removed the count down latch in the previous commit.

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PR Review Comment: https://git.openjdk.org/jdk/pull/29493#discussion_r2760762631