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Showing posts from March, 2012

Impure world resurrection: optimize for responsiveness

In the previous article I discussed a design of a computation system with non-deterministic evaluation order in context of parallelization. But there is also another, much more interesting thing which it can do: As evaluation order is non-deterministic, it is possible to prioritize code execution on a very fine-grained level -- not on level of threads, but on level of individual computations and I/O operations. Moreover, due to runtime traversal it is possible to prioritize things on fly, according to run-time needs. E.g. according to user's input. Do you see what I mean? If it is possible to identify most desired computational goals, then it's possible to prioritize them at runtime, so they are reached in lowest time possible. From user's perspective this means responsiveness: he doesn't have to wait, computer reacts to his actions immediately. Well, in ideal case. While computers became orders of magnitude faster in a last couple of decades, in many cases responsiv…

Impure world resurrection: Implicit parallelism through non-deterministic evaluation strategy with implicit side-effect control

When I've found out that there exists a pure functional programming language which is actually practical (Haskell), I was excited: I expected that pureness would allow optimizations such as automatic memoization and parallelism. However, when i started learning Haskell I was surprised that even though memoization and parallelisation are possible, they have to be explicit. Later I understood a reason for this: Haskell has a deterministic evaluation order, it is lazy unless you explicitly demand eager computation. With deterministic evaluation performance is also deterministic: programmer can expect certain performance characteristics from certain algorithms. So you wouldn't be surprised by out-of-memory condition caused by memoization and speculative execution. That's nice. Haskell's pureness allows one to make sure that parallelization is safe, but compiler won't make decisions for you. (Although it can do an optimization if it can prove that it won't make per…