support for a timeout limit when executing JS within a context

lib/rhino/context.rb

@@ -153,6 +153,24 @@ module Rhino
         nil
       end
     end
+
+    def timeout_limit
+      restrictable? ? @native.timeout_limit : false
+    end
+    
+    # Set the duration (in seconds e.g. 1.5) this context is allowed to execute.
+    # After the timeout passes (no matter if any JS has been evaluated) and this
+    # context is still attempted to run code, a #Rhino::ScriptTimeoutError will
+    # be raised.
+    def timeout_limit=(limit)
+      if restrictable?
+        @native.timeout_limit = limit
+      else
+        warn "setting an timeout_limit has no effect on this context, use " + 
+             "Context.open(:restricted => true) to gain a restrictable instance"
+        nil
+      end
+    end
     
     def optimization_level
       @native.getOptimizationLevel
@@ -260,16 +278,13 @@ module Rhino
     
     # protected void observeInstructionCount(Context context, int instructionCount)
     def observeInstructionCount(context, count)
-      if context.is_a?(Context)
-        context.instruction_count += count
-        context.check!
-      end
+      context.check!(count) if context.is_a?(Context)
     end
     
     # protected Object doTopCall(Callable callable, Context context, 
     #                            Scriptable scope, Scriptable thisObj, Object[] args)
     def doTopCall(callable, context, scope, this, args)
-      context.instruction_count = 0 if context.is_a?(Context)
+      context.reset! if context.is_a?(Context)
       super
     end
     
@@ -290,22 +305,61 @@ module Rhino
         @instruction_limit = limit
       end
 
-      attr_accessor :instruction_count
+      attr_reader :instruction_count
+      
+      TIMEOUT_INSTRUCTION_TRESHOLD = 42
+      
+      attr_reader :timeout_limit
+      
+      def timeout_limit=(limit) # in seconds
+        treshold = getInstructionObserverThreshold
+        if limit && (treshold == 0 || treshold > TIMEOUT_INSTRUCTION_TRESHOLD)
+          setInstructionObserverThreshold(TIMEOUT_INSTRUCTION_TRESHOLD)
+        end
+        @timeout_limit = limit
+      end
+      
+      attr_reader :start_time
+      
+      def check!(count = nil)
+        @instruction_count += count if count
+        check_instruction_limit!
+        check_timeout_limit!(count)
+      end
 
-      def check!
+      def check_instruction_limit!
         if instruction_limit && instruction_count > instruction_limit
           raise RunawayScriptError, "script exceeded allowable instruction count: #{instruction_limit}"
         end
       end
-
-      private
-
-        def reset!
-          self.instruction_count = 0
-          self.instruction_limit = nil
-          self
+      
+      def check_timeout_limit!(count = nil)
+        if timeout_limit
+          elapsed_time = Time.now.to_f - start_time.to_f
+          if elapsed_time > timeout_limit
+            raise ScriptTimeoutError, "script exceeded timeout: #{timeout_limit} seconds"
+          end
+          # adapt instruction treshold as needed :
+          if count
+            treshold = getInstructionObserverThreshold
+            if elapsed_time * 2 < timeout_limit
+              next_treshold_guess = treshold * 2
+              if instruction_limit && instruction_limit < next_treshold_guess
+                setInstructionObserverThreshold(instruction_limit)
+              else
+                setInstructionObserverThreshold(next_treshold_guess)
+              end
+            end
+          end
         end
-
+      end
+      
+      def reset!
+        @instruction_count = 0
+        @start_time = Time.now
+        self
+      end
+      
     end
     
   end
@@ -315,5 +369,8 @@ module Rhino
 
   class RunawayScriptError < ContextError # :nodoc:
   end
+
+  class ScriptTimeoutError < ContextError # :nodoc:
+  end
   
 end

spec/rhino/context_spec.rb

@@ -89,5 +89,55 @@ describe Rhino::Context do
       context.eval %Q{ for (var i = 0; i < 100; i++) Number(i).toString(); }
     }.should_not raise_error(Rhino::RunawayScriptError)
   end
+
+  it "allows a timeout limit per context" do
+    context1 = Rhino::Context.new :restrictable => true, :java => true
+    context1.timeout_limit = 0.3
+    
+    context2 = Rhino::Context.new :restrictable => true, :java => true
+    context2.timeout_limit = 0.3
+    
+    lambda {
+      context2.eval %Q{ 
+        var notDone = true; 
+        (function foo() { 
+          if (notDone) { 
+            notDone = false;
+            java.lang.Thread.sleep(300);
+            foo();
+          } 
+        })(); 
+      }
+    }.should raise_error(Rhino::ScriptTimeoutError)
+    
+    lambda {
+      context1.eval %Q{ 
+        var notDone = true; 
+        (function foo { 
+          if (notDone) { 
+            notDone = false;
+            java.lang.Thread.sleep(100);
+            foo();
+          } 
+        })(); 
+      }
+    }.should_not raise_error(Rhino::RunawayScriptError)
+  end
+  
+  it "allows instruction and timeout limits at the same time" do
+    context = Rhino::Context.new :restrictable => true, :java => true
+    context.timeout_limit = 0.5
+    context.instruction_limit = 10000
+    lambda {
+      context.eval %Q{ for (var i = 0; i < 100; i++) { java.lang.Thread.sleep(100); } }
+    }.should raise_error(Rhino::ScriptTimeoutError)
+    
+    context = Rhino::Context.new :restrictable => true, :java => true
+    context.timeout_limit = 0.5
+    context.instruction_limit = 1000
+    lambda {
+      context.eval %Q{ for (var i = 0; i < 100; i++) { java.lang.Thread.sleep(10); } }
+    }.should raise_error(Rhino::RunawayScriptError)
+  end
   
 end