Re: Memory allocation overhead

>>>>> "Eric" == Eric Bezault <[email protected]> writes:

    >> Are other features of MEMORY (such as allocate_fast and
    >> set_memory_threshold) implemented?

    Eric> Not yet in gec. And I haven't studied yet whether the Boehm
    Eric> GC would provide such functionality.

OK.

But in any case, I am fairly confident that I know what the basic
problem I have is. Fixing it is another matter.

XSLT is largely concerned with manipulating strings. So I think the
lack of read-only strings, enabling substring to avoid copying the
string contents, is likely a very major factor.

I have some evidence in support of this.

1) The runtime of my program is non-linear wrt the size of the input
data set.
2) If I use the tiny tree implementation for the input data set, the
runtime increases by more than 4 times.

The tiny tree implementation is an application of
the flyweight pattern, designed to reduce the number of objects
created. I copied the idea from Saxon (the contents of all text and
comment nodes is held as a single STRING object within the document,
and access to it is by substring, avoiding creating text and comment
node objects for this purpose), but I overlooked that substring copies
the data in Eiffel.

Accordingly, I think I shall abandon my efforts for now, and pursue
Manu's suggestion in FreeELKS for an aliased substring feature (I
think full copy-on-write semantics will need to be available for
STRINGs). 
I don't doubt that there are opportunities to improve my use of
STRINGs in the code (a review would help), but I think this needs
tackling first.
-- 
Colin Adams
Preston Lancashire

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