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aoli-alon Linux 7.2

I'm using a recently released laptop, and Linux hardware support hasn't caught up yet. So I've been following the changelogs of recent kernel releases to understand the current state of support.

aoli-alon 2026: The Year of Java in the Terminal?

My biggest complaint about Java development is the state of LSP/DAP support. I’ve tried writing Java in VS Code, and the support is still very incomplete. There are two features I want the most: (1) automatically downloading source code for dependencies, and (2) pausing all threads when a breakpoint is hit (https://github.com/microsoft/vscode-java-debug/issues/722 ).

I can’t find any editor or IDE that comes close to IntelliJ. If we want Java in the terminal, we may also need to think how to write Java in the terminal or are they orthogonal?

aoli-alon I took all my projects off the cloud, saving thousands of dollars

It is hilarious to read the title: "I took all my projects off the cloud [...]" and then you click the link it says: "Webserver is down".

aoli-alon Discovering a JDK Race Condition, and Debugging It in 30 Minutes with Fray

Yes, Fray controls all application threads so it runs one test per JVM. But you can always use multiple JVMs run multiple tests[1].

Fray currently does not support virtual threads. We do have an open issue tracking it, but it is low priority.

[1]: https://docs.gradle.org/current/userguide/java_testing.html#...

aoli-alon Discovering a JDK Race Condition, and Debugging It in 30 Minutes with Fray

The "randomness" comes from Kotlin coroutines and user-space scheduling. For example, Kotlin runs multiple user-space threads on the same physical thread. Fray only reschedules physical threads. So when testing applications use coroutine/virtual threads, Fray cannot generate certain thread interleavings. Also, It cannot deterministically replay because the thread execution is no longer controlled by Fray.

In our paper, we found that Fray suffers from false negatives because of this missing feature. Lincheck supports Kotlin coroutines so it finds one more bug than Fray in LC-Bench.

We didn't make any claims about false positives in Lincheck.

aoli-alon Discovering a JDK Race Condition, and Debugging It in 30 Minutes with Fray

should be fixed as well :)

aoli-alon Discovering a JDK Race Condition, and Debugging It in 30 Minutes with Fray

Thanks for pointing it out! Just did a quick fix using Claude :)

aoli-alon Systems Correctness Practices at Amazon Web Services

https://github.com/cmu-pasta/fray

Is a concurrency testing framework for Java. It also does deterministic simulation.

aoli-alon Show HN: CodeTracer – A new time-traveling debugger implemented in Nim and Rust

https://github.com/cmu-pasta/fray

Fray is a controlled concurrency testing tool for the JVM that supports record and replay. It could be a perfect backend for codetracer. (I'm the author of Fray)

aoli-alon Chrome Returns 206 when the Server Returns 403

I'm the author of the post.

I'm not sure Chrome's current caching behavior is helpful because the second response does not indicate which part of the data is returned. So, the application has no choice but to discard the data.

But thank you for your comments. This helped me to crystalize why I think this is a bug.

aoli-alon Concurrency bugs in Lucene: How to fix optimistic concurrency failures

AFAIK, Antithesis uses a hypervisor to achieve deterministic execution. This can be less effective because the hypervisor does not have language semantics and faces a larger search space. You may check Figures 5 and 6 in our technical report[1], where we compare Fray against RR, a record and replay tool that can also be used for concurrency testing at OS level[2].

[1]: https://arxiv.org/pdf/2501.12618

[2]: https://robert.ocallahan.org/2016/02/introducing-rr-chaos-mo...

aoli-alon Concurrency bugs in Lucene: How to fix optimistic concurrency failures

Using Fray does not require knowledge about "deterministic testing" or "controlled concurrency." This is one of its goals: developers write normal concurrency tests, and Fray controls the execution behind the scenes.

In fact, when we evaluate Fray, we collect all existing concurrency tests from Lucene, Kafka, and Guava, and running them under different thread inter-leavings can already reveal so many bugs. [1]

[1]: https://github.com/cmu-pasta/fray/blob/main/docs/bugs.md

aoli-alon Concurrency bugs in Lucene: How to fix optimistic concurrency failures

Fray does not know if a program is free of data races. Even if there are data races in a program, Fray can still find bugs, but this violates the soundness guarantee, so Fray may miss data race bugs.

aoli-alon Concurrency bugs in Lucene: How to fix optimistic concurrency failures

This looks super cool!

It seems that all controlled threads are wrapped with `InterceptibleThread` in the Cassandra simulator. Does this work for ThreadPools (e.g., ForkJoinPool) as well? We had a hard time intercepting thread objects because they are used by the language runtime (e.g., GC threads) as well and we don’t want to interfere with them. Additionally, modifying application code just track thread creation isn’t ideal. To work around this, we came up with this combination of JVMTi and Java Agent solution and we use JVMTi to monitor thread creation and termination.

As for searching schedules, yes, it is hard to search all possible schedules. However, it turns out many searching algorithms such as probabilistic concurrency testing[1] or partial order sampling[2] are still better than random walk. So it is worth to give them a try.

[1] https://www.microsoft.com/en-us/research/wp-content/uploads/... [2] https://www.cs.columbia.edu/~junfeng/papers/pos-cav18.pdf

aoli-alon Concurrency bugs in Lucene: How to fix optimistic concurrency failures

I’m the author of Fray, a concurrency testing framework for the JVM, and I’m excited to finally share what I’ve been building over the past few years!

Fray[1] is a concurrency testing tool for Java that can help you find and debug tricky race conditions that manifest as assertion violations, run-time exceptions, or deadlocks. I’d love to hear your thoughts—feel free to ask me anything! And if you’re curious, give Fray a try.

[1]: https://github.com/cmu-pasta/fray