[remexre]

> In Java, the compiler inserts null checks before every single dereference and throws an exception for null references.

Doesn't OpenJDK install a SIGSEGV handler, and generate the exception from that on a null dereference?

(AFAIK, a lot of runtimes for GC'd languages that support thread-based parallelism do so anyway, because they can use mprotect to do a write barrier in hardware.)

[trealira]

> Doesn't OpenJDK install a SIGSEGV handler, and generate the exception from that on a null dereference?

I thought I had read that they explicitly don't do that, but I can't find it anymore. You may be right. I should have checked before saying that.

> (AFAIK, a lot of runtimes for GC'd languages that support thread-based parallelism do so anyway, because they can use mprotect to do a write barrier in hardware.)

That's true. I guess those implementations must do something more advanced than "throw a NullPointerException if the program segfaults," given their garbage collector runtimes also rely on that signal.

[vips7L]

> I thought I had read that they explicitly don't do that

This is exactly what they do: https://shipilev.net/jvm/anatomy-quarks/25-implicit-null-che...

When this happens it'll cause a deoptimization and recompilation of the code to include the null check rather than rely on the signal handler repeatedly.

[trealira]

Thanks for the link!