Handling of USR2 signal in JVM on Linux

[Alan Bateman]

On 14/06/2022 10:44, Andrey Turbanov wrote:
> Hello.
> During investigation of signal handling in JVM (for
> https://github.com/openjdk/jdk/pull/9100#discussion_r894992558 )
> I found out that sending USR2 crashes my JDK. (Linux fastdebug x64)
>
> kill -USR2 1346792
>
> # assert(thread != __null) failed: Missing current thread in SR_handler
> # Internal Error
> (/home/turbanoff/Projects/official_jdk/src/hotspot/os/posix/signals_posix.cpp:1600),
> pid=1346792, tid=1346792
>
> Full hs_err_pid1346792.log:
> https://gist.github.com/turbanoff/2099327ea13357a90df43a2d6b0e2e6a
>
>
> Is it known/expected behaviour?
> I found some description there
> https://docs.oracle.com/en/java/javase/11/troubleshoot/handle-signals-and-exceptions.html
> that USR2 is used for SUSPEND/RESUME. Is it supported by Hotspot?

In general you have to be very careful when using signals. Yes, it can 
easily break things and probably notice it quickly with debug builds as 
asserts are compiled in to the builds (like the above). So I think 
you've found the right page to read up on this. In this case, you can 
set _JAVA_SR_SIGNUM to specify a different signal for S/R.

-Alan