Lazy loading of deferred libraries

runtime/lib/lib_prefix.dart

 // Copyright (c) 2014, 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.
 
 import "dart:async";
 import "dart:isolate";
 
 // This type corresponds to the VM-internal class LibraryPrefix.
+class _LibraryPrefix {
 
-class _LibraryPrefix {
-  _load() native "LibraryPrefix_load";
+  bool _load() native "LibraryPrefix_load";
+
+  void _invalidateDependentCode()
+      native "LibraryPrefix_invalidateDependentCode";
 
   loadLibrary() {
-    var completer = new Completer<bool>();
+    var completer = _outstandingLoadRequests[this];
+    if (completer != null) {
+      return completer.future;
+    }
+    completer = new Completer<bool>();
+    _outstandingLoadRequests[this] = completer;
     var port = new RawReceivePort();

[Ivan Posva, 2014/06/12 23:05:11]

We can simplify this with Timer.run(() {...}).

[hausner, 2014/06/12 23:54:37]

Done.

     port.handler = (_) {
-      this._load();
-      completer.complete(true);
+      var hasCompleted = this._load();
+      if (hasCompleted) {
+        _invalidateDependentCode();

[Ivan Posva, 2014/06/12 23:05:11]

How about a comment explaining why this is needed?

[hausner, 2014/06/12 23:54:37]

Done.

+        completer.complete(true);
+        _outstandingLoadRequests.remove(this);
+      }
       port.close();
     };
     port.sendPort.send(1);
     return completer.future;
   }
 }
+
+var _outstandingLoadRequests = new Map<_LibraryPrefix, Completer>();
+
+
+// Called from the VM when all outstanding load requests have
+// finished.
+_completeDeferredLoads() {
+  var lenghth = _outstandingLoadRequests;
+  _outstandingLoadRequests.forEach((prefix, completer) {
+    prefix._invalidateDependentCode();
+    completer.complete(true);
+  });
+  _outstandingLoadRequests.clear();
+}