Riskless deletion of nested structures

[Christian Tismer]

Howdy,

Please review!

While implementing Stackless Python, a new problem arose:
Nested structures like frame chains and tracebacks can now
easily grow somuch that they cause a stack overflow on deallocation.

To protect lists, tuples, frames, dicts and tracebacks against
this, I wrote a stackless deallocator.
At the moment, everything is done in trashcan.c .
This gives a slight performance loss of 5% for pystone, most probably
due to the double indirection and non-local code reference.
It is yet a hack, since I'm grabbing the tp->dealloc pointers of these
types and replace them by safe versions. This just in order to
try out things quickly. Later I will change this and incorporate
the stack checks into the affected modules, after I got some
feedback on this.

This patch applies to Stackless and standard Python as well:
Deallocation of deeply nested structures will never again cause
a stack overflow.

Installation for the intermediate version:
Insert a line

	_Py_trashcan_install();

at the end of Py_Initialize in pythonrun.c

Please try it and check my code wether there is a better solution.

cheers - chris

-- 
Christian Tismer             :^)   <mailto:tismer at appliedbiometrics.com>
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