问题
I am using the .NET API of Z3. When I instantiate a solver by calling:
Solver s = ctx.MkSolver(ctx.TryFor(ctx.MkTactic("qflia"), TimeLimit));
and give it a TimeLimit of 60 seconds (60000 milliseconds) for some models the statement
s.Check()
does not return after 60 seconds. For some models it returns a few seconds later, which in my case would not be a problem, but for some models it doesn't return at all (I cancelled the process after 3 days).
How can I force Z3 to stop checking after a given timelimit?
回答1:
The TryFor combinator is implemented using a "cancellation" flag. The new tactics are very responsive, and terminate very quickly when the "cancellation" flag is set. Unfortunately, the general purpose tactic smt is a wrapper over a general purpose solver. This general purpose solver is not very responsive. It can get "lost" in several key places: quantifier instantiation, Simplex, etc. The qflia tactic is built on top of the smt and many other tactics. Since, you are trying to solve quantifier-free problems. I'm assuming that the smt tactic is in a loop inside of the Simplex module. The Simplex module in the smt tactic is implemented using arbitrary precision rational numbers. Thus, it may be very time consuming for non-trivial linear real/integer problems.
There is not much you can do to workaround this issue. If you really need a strong guarantee in running time, the only solution I see is to create a separate process running Z3, and kill it whenever it takes more the k seconds to solve a problem.
That being said, future versions of Z3 will have a complete new arithmetic module. This new module (like the new tactics) will terminate quickly when the cancellation flag is set.
来源：https://stackoverflow.com/questions/11923957/tryfor-in-z3-does-not-stop-checking-after-the-given-timelimit