Heisenbug involving Destructors & GC - Help Needed

[Etienne Cimon via Digitalmars-d]

On 2015-06-26 14:27, Maxime Chevalier-Boisvert wrote:
> I seem to have run into a heisenbug involving destructors and the GC.
> I'm kind of stuck at this point and need help tracking down the issue.
>
> I put the broken code in a branch called heisenbug on github:
> https://github.com/higgsjs/Higgs/tree/heisenbug
>
> The problem manifests itself on runs of `make test` (my unittests), but
> only some of the time. I wrote a script to run `make test` repeatedly to
> try and find a solution:
> https://github.com/higgsjs/Higgs/blob/heisenbug/source/repeatmaketest.py
>
> The problem usually manifests itself after 5 to 15 runs on my machine. I
> get a segmentation fault, not always in the same place. The randomness
> seems to stem from address space randomization.
>
> It seems the issue is caused by my freeing/reinitializing the VM during
> unit tests. More specifically, commenting out this line makes the
> problem go away:
> https://github.com/higgsjs/Higgs/blob/heisenbug/source/runtime/vm.d#L741
>
> Higgs can run all of my benchmarks without ever failing, but restarting
> the VM during `make test` seems to be causing this problem to happen.
> It's not impossible that there could be another underlying issue, such
> as the JITted code I generate corrupting some memory location, but it
> would seem that if this were the case, the issue would likely show up
> outside of unit tests. Any help would be appreciated.

This might come as a surprise to you as much as it did to me at the 
time, but when you have GCRoot* root; where GCRoot is a struct, if you 
destroy(root), you're setting your local pointer to null. You're not 
actually calling the destructor on the struct.

Also, I would avoid throwing of any type in a destructor.

https://github.com/higgsjs/Higgs/blob/0b48477120c4acce46a01b05a1d4b035aa432550/source/jit/codeblock.d#L157