Author: Tim Mann
Date: 20:56:48 01/05/01
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John sent me some email about this, and so I can explain where he is coming from. CM8000 has a feature that allows the user to pause the game and stop the clocks. They would like this to also pause the engine's search (or pondering), but the WinBoard protocol doesn't document a way to do that. John's question was whether "force" causes the engine to clear its transposition hash table. If it doesn't, then if the GUI wants to pause the search, it could send "force". It would later send "go" (or "playother" if the engine is not on move and supports the playother command) to resume the search. If the hash table was not cleared, then the search should quickly get back to roughly where it was when paused, achieving the desired effect. Gian-Carlo is of course correct in saying that the protocol doesn't specify what should happen in this case, so some engines may clear the hash tables and some may not. (Also, of course, some simple engines don't even have hash tables.) I'm thinking of adding another optional feature to the WinBoard protocol that allows the engine to say "it's okay to use force to pause and resume a search". Or maybe instead, I would add a new optional command "pause", which is the same as "force" except that the engine tries to save its search state so that it can resume if "go" or "playother" is sent without changing the position. Not clearing the hash table would be one good way to implement saving the search state, though an engine author could choose to do it some other way. Comments are welcome... I am going to post this to the chess-engines mailing list too. --Tim
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