Hi all, I did some tests witha C-based vhash implementation, it's possible to increse the speed by 30x compared to current vlist imlpementation in guile. It would be possible to get this speed today if one implemented vhash-assoc as a VM op. Anyway using the source as a standard lib will get you about 10x speed increase.
Another pressing need is that vhashes are not thread safe, also a downside is that if there are many versions spawned by each vhash the good theoretical properties may not realize. Anyway here is a suggestion of how to make it thread safe: 1. keep two numbers seq-int and thread-id on the block. thread-id is a unique id for a thread. And seq-id is a unique id for a state. 2. At thread-creation in thread 1 spawning thread 2. increment thread 1's seq-id, and allocate a new id to thread 2 and set it's seq-id to zero. 3. Att vhash-cons, if not the vhash seq-id and thread-id matches we must create a new block pointing to the old vhash with size equal to k. 4. this is thread safe and will not waste space, but can create problems with lot's of small blocks linked and essentially get a sort of linked list the computational lookup is o(T), T is the number of threads. 5. If we get an issue with lot's of small block linked together we could detect this and issue a "remake" in order to speed up access times. This is not a problem that is unique to threading but can be seen in a naive use of vhashes for many applications that backtracks and use old copies of vhashes. So a solution of autocompilation would be needed. 6. I plan to add a version of vhashes to guile-log as a replacement of the assoc list. What I will then use is to tag vhash blocks as referenced and when backtracking and the block is not referenced it will simply reset the offset pointer and reuse the block-frame instead of linking another one to it. Some kind of reference counter technique would be used here. n guile-log we have good control on when we reference for storage so this solution would probably work just great. With all this implementing good thread safe ideoms into guile-log would be quite possible. Regards Stefan
