[Cython] AddTraceback() slows down generators

[Stefan Behnel]

Stefan Behnel, 27.01.2012 09:02:
> any exception *propagation* is
> still substantially slower than necessary, and that's a general issue.

Here's a general take on a code object cache for exception propagation.

https://github.com/scoder/cython/commit/ad18e0208

When I raise an exception in test code that propagates through a Python
call hierarchy of four functions before being caught, the cache gives me
something like a 2x speedup in total. Not bad. When I do the same for cdef
functions, it's more like 4-5x.

The main idea is to cache the objects in a reallocable C array and bisect
into it based on the C code "__LINE__" of the exception, which should be
unique enough for a given module.

It's a global cache that doesn't limit the lifetime of code objects  (well,
up to the lifetime of the module, obviously). I don't know if that's a
problem because the number of code objects is only bounded by the number of
exception origination points in the C source code, which is usually quite
large. However, only a tiny fraction of those will ever raise or propagate
an exception in practice, so the real number of cached code objects will be
substantially smaller.

Maybe thorough test suites with lots of failure testing would notice a
difference in memory consumption, even though a single code objects isn't
all that large either...

What do you think?

Stefan