lifetimes [Re: alloca() portability]

[Ozan Yigit]

In article <2183 at kraftbus.opal.cs.tu-berlin.de> 
net at tubopal.UUCP (Oliver Laumann) writes:
>This, of course, doesn't work when the amount of data to be stored
>in the local buffer can't be determined at compile time.  If it were
>known at compile time, there would be no need to use alloca() in the
>first place.

Yes, Oliver, that example is somewhat restricted, but there *are* methods
to allocate and de-allocate memory almost as conveniently and speedily as
the usual stack allocation. You may wish to check out the following:

%A David R. Hanson
%T Fast Allocation and Deallocation of Memory Based on Object
Lifetimes
%J Software - Practice and Experience
%V 20
%N 1
%D Jan 1990
%P 5-12

In this scheme, lifetime-indexed linked arenas are used for allocation.
The allocation code is very simple and in-line. The algorithm totally
avoids per-object de-allocation by using the lifetimes to reclaim the
arenas.  This allocator was developed as a way to improve the
de-allocation speed of various data structures such as symbol-table
entries, nodes for trees and dags in a C compiler. 

I think algorithms such as this one make further alloca discussions
about as useful as alloca itself. :-)

oz
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