Re: [Xsb-development] The thread that won't die

[<ki...@cs...>]

Terry wrote:
>
> Whatever the semantics of assert and retract should be, I dont think
> we should go into infinite loops.

Bart would call it the "infinite loop" (INFLOOP) semantics :-)


> So my proposal is to put a "lock" on asserted/interned tries by having
> the first instruction of these tries be choice point that implements a
> simple "lock" that ensures that the same trie cannot be both written
> to and read from at the same time.

What does it mean in practical terms? That backtracking over predicate
being updated is not allowed, but you would get an error message?


> The lock is acquired either by one_node_check_insert() or by executing
> the first choice point in an asserted trie, and will allow any number
> of readers *or* a single writer.
> 
> The lock is released at the end of one_node_check_insert() or when
> backtracking out of the trie.

Is it possible to get deadlocked under this schema? Say, the clause aborts
or is cut. I suppose the lock will also be released?

Thanks for looking into this. I suspected that there is more to this
example than simply backtracking over an update. Usually when I backtrack
over an update I get hit by the SIGSEGV semantics, not the INFLOOP one :-)


	--michael