support optimizer-specific stopping checks

Author: alyst

src/opt_controller.jl

@@ -201,7 +201,11 @@ function check_stop_condition(ctrl::OptRunController)
         return "Max number of steps ($(ctrl.max_steps)) reached"
     end
 
-    return check_stop_condition(ctrl.evaluator, ctrl)
+    eval_check = check_stop_condition(ctrl.evaluator, ctrl)
+    isempty(eval_check) || return eval_check
+
+    optimizer_check = check_stop_condition(ctrl.optimizer, ctrl)
+    return optimizer_check
 
     return "" # empty string, no termination
 end

src/optimizer.jl

@@ -3,6 +3,9 @@ Base abstract class for black-box optimization algorithms.
 """
 abstract type Optimizer end
 
+# by default optimizer doesn't check for stopping conditions
+check_stop_condition(o::Optimizer, ctrl) = ""
+
 """
 Optimizers derived from `SteppingOptimizer` implement classical iterative optimization scheme
 `step!()` → `step!()` → …