Canceling an asynchronous solve operation does not always work.

[rkaminsk]

I have been experimenting with the following program:

#script (python) 

import clingo

def main(prg):
    prg.ground([("pigeon", [])])
    for i in range(0,2):
        prg.assign_external(clingo.Function("p"), True)
        prg.solve()
        prg.assign_external(clingo.Function("p"), False)
        with prg.solve(async=True) as handle:
            #print "wait"
            #handle.wait(0.01)
            print "cancel"
            handle.cancel()

#end.

#const n = 190.

#program pigeon.
#external p.

1 { p(X); q(X) } 1 :- X = 1..n, not p.
:- not n+1 { p(1..n); q(1..n) }, not p.

As long as there is a small wait before an asynchronous solve operation is canceled things work fine. But when the search operation is canceled immediately, the above program consistently hangs. (The program will not be solved in the lifetime of our solar system.) The python wait and cancel calls directly map to clasp API calls in ClaspFacade::SolveHandle.

[BenKaufmann]

Thanks. Should be fixed.