A couple garbage collector questions
Jeremy Hylton
jeremy at digicool.com
Tue Apr 10 11:52:09 EDT 2001
Hannah,
This would be a mammoth project for Python. The Python VM performs
reference counting without any compiler support. The compiler emits
an instruction like DUP_TOP (duplicate object on top of stack). The
VM incremenents the reference count of the object as part of the
DUP_TOP implementation.
The Python VM instructions are high level and, thus, fairly
expensive. To get compiler support for managing reference counts,
we'd need to go with a completely different VM that included reference
count operations as part of the instruction set. The current
per-instruction overhead would dwarf the cost of the ref counts. So
without a significant redesign, this approach would probably slow down
the interpreter enormously.
The idea seems reasonable, so far as I can tell. But we have neither
the compiler infrastructure nor the VM support we would need to make
it work.
Jeremy
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