> 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.
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.
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.