implement locking

Author: guybedford

lib/loader.js

@@ -687,13 +687,18 @@ function logloads(loads) {
         // NB This should be an Object.defineProperty, but that is very slow.
         //    By disaling this module write-protection we gain performance.
         //    It could be useful to allow an option to enable or disable this.
+        module.locked = true;
         moduleObj[name] = value;
 
         for (var i = 0, l = module.importers.length; i < l; i++) {
           var importerModule = module.importers[i];
-          var importerIndex = importerModule.dependencies.indexOf(module);
-          importerModule.setters[importerIndex](moduleObj);
+          if (!importerModule.locked) {
+            var importerIndex = importerModule.dependencies.indexOf(module);
+            importerModule.setters[importerIndex](moduleObj);
+          }
         }
+
+        module.locked = false;
         return value;
       });
 

test/syntax/circular1.js

@@ -2,6 +2,8 @@ import {fn2, variable2} from './circular2';
 
 export var variable1 = 'test circular 1';
 
+export { output as output2 } from './circular2';
+
 fn2();
 
 export var output;

test/test.js

@@ -212,7 +212,8 @@ function runTests() {
         assert(
           [m2.output, 'test circular 1'],
           [m1.output, 'test circular 2'],
-          [m2.output1, 'test circular 2']
+          [m2.output1, 'test circular 2'],
+          [m1.output2, 'test circular 1']
         );
       }, err);
     }, err);