[Python-Dev] Tagged integers (original) (raw)

Christian Tismer tismer at stackless.com
Thu Jul 15 12:04:18 CEST 2004

Brian Quinlan wrote:

...

And the lack of portability is a real problem - it means that every code path must be tested twice AND there might be architectures and problems were tagged integers work but it actually makes things slower.

I think it was not the proposal to use tagging on every platform, but just those where it works. Having this as a compile time feature would make it possible to optimize your Python for your purposes.

Things get interesting when it comes to compare refcounting cost vs. pointer decoding cost vs. garbage collection cost.

I have no idea what the results will be, and I think it is just great to try this out, because the effect could be dramatic:

If very many tiny, often-used objects are tagged, then very many refcount actions can be saved, and the overall object count shrinks, Boehm GC might become feasible. If we then can write C extensions without having to think of reference counts, code would be simplified quite much, and I would save 80 percent of debugging time.

Maybe we have a set of rules which depend on each other:

  1. "Tagging is -1000 because of the headaches"

  2. "Everything is object and has refcount"

  3. "Many tiny objects must be allocated as blocks"

  4. "Boehm GC disables bulk allocation of tiny objects"

  5. is just a claim which I would not sign, see the post about systematically renaming fields to find all places with the compiler.

  6. leads to 2), 2) leads to 3), and this disables using 4). By solving 1), it might be possible to break the whole chain, and I would even accept a slitghly slower result, if the whole system gets simpler by dropping refcounts.

So whatever is the outcome, I'm happy that somebody took it on to try this out.

ciao - chris

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