[r6rs-discuss] Implicitly Concurrent Scheme
cowan at ccil.org
Fri Nov 6 03:42:10 EST 2009
Marc Feeley scripsit:
> Not true. Lazy-task creation will do a very good job dynamically.
> Read my PhD thesis for details:
Well, I have read the whole thesis now (impressive stuff) and it still
seems to me that near the leaves of a spawning tree there comes a
point when the overhead, however small, must exceed the overhead of the
fork/join operations, however efficient. Consider the sum benchmark
(which, for the rest of you, adds up the elements of an array of size
2^n by divide-and-conquer, splitting the array in half repeatedly until
one is adding two elements in each leaf thread).
Can it really be that it is more efficient to add four numbers in two
threads than in one thread? Somewhere, exactly where will depend
on implementation details, one must cross the line where constant
factors dominate. And that is not a point that, in the general case,
will be known.
John Cowan http://ccil.org/~cowan cowan at ccil.org
In might the Feanorians / that swore the unforgotten oath
brought war into Arvernien / with burning and with broken troth.
and Elwing from her fastness dim / then cast her in the waters wide,
but like a mew was swiftly borne, / uplifted o'er the roaring tide.
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