Very simple version of Isolates.

runtime/bin/main.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include <stdlib.h>
 #include <string.h>
 #include <stdio.h>
 
 #include "include/dart_api.h"
 #include "include/dart_debugger_api.h"
@@ skipping 863 matching lines @@
                          Dart_GetError(result));
       }
     }
     if (has_print_script) {
       result = GenerateScriptSource();
       if (Dart_IsError(result)) {
         return DartErrorExit(result);
       }
     } else {
       // Lookup and invoke the top level main function.
-      Dart_Handle main_args[1];
+      // The top-level function may accept up to two arguments:
+      //   main(List<String> args, var message).
+      // However most commonly it either accepts one (the args list) or
+      // none.
+      // If the message is optional, main(args, [message]), it is invoked with
+      // one argument only.
+      Dart_Handle main_args[2];
       main_args[0] = CreateRuntimeOptions(&dart_options);
+      main_args[1] = Dart_Null();
+      // First try with 1 argument.
       result = Dart_Invoke(library, DartUtils::NewString("main"), 1, main_args);
       // TODO(iposva): Return a special error type for mismatched argument
       // counts from Dart_Invoke to avoid the string comparison.
       const char* expected_error = "Dart_Invoke: wrong argument count for "
-          "function 'main': 1 passed, 0 expected.";
+          "function 'main': ";
+      intptr_t length = strlen(expected_error);
       if (Dart_IsError(result) &&
-          strcmp(expected_error, Dart_GetError(result)) == 0) {
-        result = Dart_Invoke(library, DartUtils::NewString("main"), 0, NULL);
+          strncmp(expected_error, Dart_GetError(result), length) == 0) {
+        // Try with two arguments.
+        result =
+            Dart_Invoke(library, DartUtils::NewString("main"), 2, main_args);
+        if (Dart_IsError(result) &&
+            strncmp(expected_error, Dart_GetError(result), length) == 0) {
+          // Finally try with 0 arguments.
+          result = Dart_Invoke(library, DartUtils::NewString("main"), 0, NULL);
+        }
       }
       if (Dart_IsError(result)) {
         return DartErrorExit(result);
       }
 
       // Keep handling messages until the last active receive port is closed.
       result = Dart_RunLoop();
       if (Dart_IsError(result)) {
         return DartErrorExit(result);
       }
@@ skipping 15 matching lines @@
 
   return Process::GlobalExitCode();
 }
 
 }  // namespace bin
 }  // namespace dart
 
 int main(int argc, char** argv) {
   return dart::bin::main(argc, argv);
 }