New submission from Mark Shannon <m...@hotpy.org>:
Currently, if a dictionary is split, then the dictionary owns the memory for the values. Unless the values is the unique empty-values array. In order to support lazily created dictionaries for objects (see https://github.com/faster-cpython/ideas/issues/72#issuecomment-886796360), we need to allow shared keys dicts that do not own the memory of the values. I propose the following changes to the internals of dict objects. Add 4 flag bits (these can go in the low bits of the version tag) 2 bit for ownership of values, the other 2 bits for the stride of the values (1 or 3). All dictionaries would then have a non-NULL values pointer. The value of index `ix` would be always located at `dict->ma_values[ix*stride]` The two ownership bits indicate whether the dictionary owns the references and whether it owns the memory. When a dictionary is freed, the items in the values array would be decref'd if the references are owned. The values array would be freed if the memory is owned. I don't think it is possible to own the memory, but not the references. Examples: A combined dict. Stride = 3, owns_refs = 1, owns_mem = 0. A split keys dict. Stride = 1, owns_refs = 1, owns_mem = 1. Empty dict (split). Stride = 1, owns_refs = 0, owns_mem = 0. Dictionary with values embedded in object (https://github.com/faster-cpython/ideas/issues/72#issuecomment-886796360, second diagram). Stride = 1, owns_refs = 0, owns_mem = 0. ---------- assignee: Mark.Shannon components: Interpreter Core messages: 402047 nosy: Mark.Shannon, methane priority: normal severity: normal status: open title: Allow split key dictionaries with values owned by other objects. _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue45233> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
