Dev Call: 4 November 2021

Present

Ronan, Stepan, Florian, Tim, Anto, Simon

Notes

• Status of Numpy
  • tp_dealloc -> tp_finalize
  • transforming tp_traverse
  • setting it up to use HPy_Field => see discussion of HPy_GetContext
• We may need a HPy_GetContext
  • otherwise almost everything needs to be migrated immediately
  • similar problems will come up when migrating pybind11, which has c++ operators which do Py_ calls
  • discussing HPy_Context stack for nested downcalls?
    • HPy_GetContext would give the top of the stack context
  • Simon proposal: HPy_MakeContext that gives you a context that you should not hold on to
  • Stepan proposal: use a trampoline to go through the runtime to call back into our converted function that takes HPy_Context*, void*
    • get the trampoline function from the context and keep it around
    • when we need a context, we call the trampoline with the migrated function that does take the context and additional void* args
• tp_finalize is supported in NumPy and can upcall arbitrary code
  • guaranteed to be called once exactly, even though it can resurrect; same as __del__ on the Python level
• weak referencable types need special handling for CPython
  • use a flag on HPy to declare a type as weak referencable