some questions about project tsan

[Arthur Eubanks]

On Thu, Jan 9, 2020 at 1:02 AM Jie He <Jie.He at arm.com> wrote:

> Hi
>
> I'm an engineer from ARM, and noticed this project is helpful to detect
> data race in Java level.
>
Thanks for the interest!

>
> I have some questions about this project:
>
> 1, how about the current status? All dev jobs have been finished already?
>
It works and we use this internally at Google. There should be no false
positives reported, but not everything is precise and there are false
negatives (e.g. final fields, finalizers, etc.). I believe the current
implementation catches most races, which is good enough, and extra effort
spent making instrumentation more precise would only find a couple more
races, which may or may not be worth the effort.
Ideally we'd like to upstream this into mainline.

> 2, for detection of data race in Java code, I think current implementation
> only in X86 is enough. A data race in java code will be found whatever the
> machine platform is.
>     So that, porting this project to AARCH64 is meaningless? Is it helpful
> to find some issues which don't happen in X86?
>
Yes a data race will likely be found on x86 and it would apply to AARCH64
as well. Porting to AARCH64 could still be interesting and useful for
people who only have AARCH64 machines. And maybe running on different
architectures will change the timing of concurrent execution, causing races
to disappear or appear.

> 3, Is there a plan to add the support to detect data race in JVM self?
> E.g. add the instrumentation into the assemble code generated by
> interpreter, compiler and runtime,
>     In some machine platforms which have weak memory model like arm and
> ppc, engineers often make mistakes when writing data race related code even
> though they are experienced.
>     I think such a tool could help to detect these bugs easily than before.
>
We've thought about this in the past, but there is a ton of intentionally
racy code. You could try adding -fsanitize=thread to the hotspot
compilations and running it just to see what would happen.

>
> Thanks
> Jie He
>