Question

My team is working on an MMO server in Ruby, and we opted to start moving computationally intensive operations into a C extension. As part of that effort, we moved the actual data storage into C (using Data_Get_Struct and all that). So, for example, each Ruby “Zone” object has an associated “ZoneKernel::Zone” C struct where the actual binary data is stored.

Basically, I’m wondering if this is a terrible idea or not. I’m not super familiar with the ruby internals, but it seems like the data should be fine as long as the parent Zone stays in memory on the ruby side (thus preventing garbage collection of the C data).

One caveat is that we’ve been getting semi-regular “Stack Consistency Errors” that crash our server – this seems like potentially a related memory issue (instead of just your garden variety segfault) – if anyone has any knowledge of what that might be, I would appreciate that as well!

Answer 1

As stated in the documentation to Data_Wrap_Struct(klass, mark, free, ptr) function:

The free argument is the function to free the pointer allocation. If
this is -1, the pointer will be just freed.

These mark / free functions are invoked during GC execution.

Your wrapped native structure will be automatically freed when its corresponding Ruby object is finalized. Until that happens, your data will not be freed unless you do so manually.

Writing C extensions doesn’t guarantee a performance boost, but it almost always increases the complexity of your code. Profile your server in order to measure your performance gains, and develop your Zone class in pure Ruby if viable.