RE: [Haskell-cafe] Re: FPS: Finalizers not running (wasMemoryusageoutside of the Haskell heap)

On 10 November 2005 14:56, Jan-Willem Maessen wrote:

On Nov 9, 2005, at 4:46 AM, Ketil Malde wrote:

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Sebastian Sylvan wrote:

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On 11/8/05, Jan-Willem Maessen wrote:

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Just wanted to let people know that I've been working on improving Data.HashTable, with the help of Ketil Malde's badly performing code

Always happy to help, of course - bad performance R us:-)

I think that if I can get unsafeFreeze/unsafeThaw to work reliably, it'll finally outperform Data.Map on your example. I haven't yet played with the hash function, which looks kind of bad; there may be hope for improvement there as well.

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Request: Data.HashTable.Immutable

I'm not sure you really want that - do you wish to copy a large array each time you do an update? Freezing and thawing might be a good idea, though.

A true read-only hash table, with a freeze for the mutable version, but NO THAW, could potentially be useful. I seem to recall that hbc had an immutable hash table (along with a derivable Hashable class), where the content was specified as in an array comprehension.

The unsafeFreeze/unsafeThaw trick can be used to speed up DiffArrays, which in turn could be used to provide a good immutable HashTable implementation. I'm pretty sure this would be a profitable approach. It's possible that DiffArrays need more work than just unsafeFreeze/unsafeThaw to make them efficient, though. Cheers, Simon