OMPL uses the ompl::base::PlannerTerminationCondition concept to let planning algorithms know that an attempt to solve a motion planning problem should be terminated. This is done by passing an instance of an ompl::base::PlannerTerminationCondition to a planner's solve method. A PlannerTerminationCondition instance is essentially a functor that can be called with zero arguments that returns true when the planner should terminate. For convenience, there is also a cast-to-bool operator defined so the following two if statements are equivalent:

// ptc is an instance of ompl::base::PlannerTerminationCondition
if (ptc()) return;
if (ptc) return;

OMPL implements several different conditions that you can use:

ompl::base::timedPlannerTerminationCondition(double): a function that returns a PlannerTerminationCondition instance that causes the planner to terminate after a fixed amount of time has been exceeded.
ompl::base::timedPlannerTerminationCondition(ompl::time::duration): same as the previous one, but using an OMPL data type to denote the duration.
ompl::base::timedPlannerTerminationCondition(double, double): a function that returns a PlannerTerminationCondition instance that causes the planner to terminate after a fixed amount of time has been exceeded. Unlike the previous function, this one spawns a separate thread where the time passed is checked every interval seconds.
ompl::base::IterationTerminationCondition: a PlannerTerminationCondition-derived class that causes a planner to terminate after its eval() method has been called numIterations times, where numIterations is an unsigned int argument to the constructor.
ompl::base::CostConvergenceTerminationCondition: a PlannerTerminationCondition-derived class that causes an optimizing planner to terminate once the cost for the best path has converged, which is defined as the cumulative moving average of the last n reported solutions changing by a factor of less than epsilon. By setting epsilon to 1, the planner will automatically terminate after exactly n solutions have been found.
ompl::base::exactSolnPlannerTerminationCondition: a function that returns a PlannerTerminationCondition instance that causes the planner to terminate after an exact (i.e., not an approximate, but possibly sub-optimal) solution has been found.
ompl::base::plannerNonTerminatingCondition: a function that returns a PlannerTerminationCondition instance that causes the planner to never terminate.
ompl::base::plannerAlwaysTerminatingCondition: a function that returns a PlannerTerminationCondition instance that causes the planner to immediately terminate.
ompl::base::plannerOrTerminationCondition: a function that, given two PlannerTerminationCondition instances c1 and c2, returns a PlannerTerminationCondition instance that causes the planner to terminate when either returns true.
ompl::base::plannerAndTerminationCondition: a function that, given two PlannerTerminationCondition instances c1 and c2, returns a PlannerTerminationCondition instance that causes the planner to terminate when both return true.

If the MORSE extension is enabled, the ompl::base::MorseTerminationCondition is also available, which is a PlannerTerminationCondition-derived class that causes a planner to terminate if the user shuts down the MORSE simulation.