We have run out of flags bits in `PyTypeObject`'s `tp_flags`
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Description
PyTypeObject's tp_flags field is defined as an unsigned long. In effect this means that we have only 32 bits we can use for flags. We have already used all 32 of them.
Bits 15 and 16 are reserved for Stackless Python. Since Stackless Python is pining for the fjords, we could recycle those two bits. However that's not going to last long with likely changes necessary for parallelism and performance.
Any change to PyTypeObject breaks both API and ABI, but that's OK because:
- Adding a field or changing the size of a field is a backwards compatible API change.
- The existence of
PyTypeObjectis part of the stable ABI, but its layout is not.
The cleanest change, IMO, is to change unsigned long tp_flags to uint64_t tp_flags which gives us another 32 bits, which should last many more years.
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with the PyTypeObject definition and all uses of its tp_flags field, then assess the proposed width change against the stated API and ABI constraints. Done means reaching and implementing an agreed design for extending the available flag bits, with affected interfaces and compatibility behavior addressed.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- backend
- Issue type
- Feature
- Difficulty
- 5/5
- Estimated time
- Over a week
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100