3 ms·

Your understanding of Rust is correct, but the code uses unsafe: https://github.com/andreabergia/rjvm/blob/93e7e48db085e780b0787aaf37bb3c77d6cfa7b8/vm/src/gc.rs

Your understanding of Rust is correct, but the code uses unsafe: https://github.com/andreabergia/rjvm/blob/93e7e48db085e780b0787aaf37bb3c77d6cfa7b8/vm/src/gc.rs#L39 https://github.com/andreabergia/rjvm/blob/93e7e48db085e780b0... As a result, when the VM gets dropped, the memory gets deallocated even if there are still objects that reference it. Somewhat related, there also is the issue that when you create multiple VMs, you can use classes/objects/… created by one VM with another.

bialpio 3y ago
IIUC this should be fine - MemoryChunk doesn't seem to deallocate the memory (so we leak), unless there's a dealloc somewhere (sorry, not logged in to GH so cannot search). Which is not the worst outcome here, because as you said, we don't want to deallocate this memory since there may be places that still refer to it... As for where the static lifetime gets into play, VM creation doesn't use unsafe & compiler is happy about it, even though ISTM that there could be a tighter bound on the lifetime? https://github.com/andreabergia/rjvm/blob/93e7e48db085e780b0787aaf37bb3c77d6cfa7b8/vm/tests/integration/real_code_tests.rs#L10 https://github.com/andreabergia/rjvm/blob/93e7e48db085e780b0...
- skitter 3y ago
  VM creation is using unsafe (the line I pointed out above). You're right, I can't find any deallocation either – but weirdly it /does/ segfault (or sometimes have other memory related errors) if I drop the VM while it's heap is still referenced. The thing with a tighter bound on the lifetime is that VM carrying a lifetime for itself is fundamentally flawed. A solution would be to remove said lifetime, and have all methods on VM that return lifetimed objects take said lifetime from the reference to the VM.
  - andreabergia 3y ago
    That sounds reasonable (and way better than what I have implemented). I am not sure I am going to try it though - it probably is a bit too much code to change for something that I consider "done" and I am not working on. :)

bialpio 3y ago

IIUC this should be fine - MemoryChunk doesn't seem to deallocate the memory (so we leak), unless there's a dealloc somewhere (sorry, not logged in to GH so cannot search). Which is not the worst outcome here, because as you said, we don't want to deallocate this memory since there may be places that still refer to it... As for where the static lifetime gets into play, VM creation doesn't use unsafe & compiler is happy about it, even though ISTM that there could be a tighter bound on the lifetime? https://github.com/andreabergia/rjvm/blob/93e7e48db085e780b0787aaf37bb3c77d6cfa7b8/vm/tests/integration/real_code_tests.rs#L10 https://github.com/andreabergia/rjvm/blob/93e7e48db085e780b0...

skitter 3y ago
VM creation is using unsafe (the line I pointed out above). You're right, I can't find any deallocation either – but weirdly it /does/ segfault (or sometimes have other memory related errors) if I drop the VM while it's heap is still referenced. The thing with a tighter bound on the lifetime is that VM carrying a lifetime for itself is fundamentally flawed. A solution would be to remove said lifetime, and have all methods on VM that return lifetimed objects take said lifetime from the reference to the VM.
- andreabergia 3y ago
  That sounds reasonable (and way better than what I have implemented). I am not sure I am going to try it though - it probably is a bit too much code to change for something that I consider "done" and I am not working on. :)