Load deferred chunks in the right order.

sdk/lib/_internal/compiler/implementation/deferred_load.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.
 
 library deferred_load;
 
 import 'dart2jslib.dart' show
     Compiler,
     CompilerTask,
     Constant,
@@ skipping 101 matching lines @@
   /// The OutputUnit that will be loaded when the program starts.
   final OutputUnit mainOutputUnit = new OutputUnit();
 
   /// A set containing (eventually) all output units that will result from the
   /// program.
   final Set<OutputUnit> allOutputUnits = new Set<OutputUnit>();
 
   /// Will be `true` if the program contains deferred libraries.
   bool splitProgram = false;
 
-  /// A mapping from the name of a [DeferredLibrary] annotation to all dependent
-  /// output units.
-  final Map<String, Set<OutputUnit>> hunksToLoad =
-      new Map<String, Set<OutputUnit>>();
+  /// A mapping from the name of a defer import to all the output units it
+  /// depends on in a list of lists to be loaded in the order they appear.
+  ///
+  /// For example {"lib1": [[lib1_lib2_lib3], [lib1_lib2, lib1_lib3],
+  /// [lib1]]} would mean that in order to load "lib1" first the hunk
+  /// lib1_lib2_lib2 should be loaded, then the hunks lib1_lib2 and lib1_lib3
+  /// can be loaded in parallel. And finally lib1 can be loaded.
+  final Map<String, List<List<OutputUnit>>> hunksToLoad =
+      new Map<String, List<List<OutputUnit>>>();
   final Map<Import, String> importDeferName = new Map<Import, String>();
 
   /// A mapping from elements and constants to their output unit. Query this via
   /// [outputUnitForElement]
   final Map<Element, OutputUnit> _elementToOutputUnit =
       new Map<Element, OutputUnit>();
 
   /// A mapping from constants to their output unit. Query this via
   /// [outputUnitForConstant]
   final Map<Constant, OutputUnit> _constantToOutputUnit =
@@ skipping 465 matching lines @@
       generatedNames[outputUnit] = outputUnit.name;
     }
 
     for (Import import in _allDeferredImports.keys) {
       computeImportDeferName(import);
     }
 
     for (OutputUnit outputUnit in allOutputUnits) {
       computeOutputUnitName(outputUnit);
     }
+    List sortedOutputUnits = new List.from(allOutputUnits);
+    // Sort the outputunits in descending order of the number of imports they

[floitsch, 2014/04/02 09:32:48]

output units

[sigurdm, 2014/04/02 11:25:30]

Done.

+    // include.

[floitsch, 2014/04/02 09:32:48]

Explain why this is necessary and enough.

[sigurdm, 2014/04/02 11:25:30]

I tried to explain it - hope it is not too verbose.

+    sortedOutputUnits.sort((a, b) => b.imports.length - a.imports.length);
 
     // For each deferred import we find out which outputUnits to load.
     for (Import import in _allDeferredImports.keys) {
       if (import == _fakeMainImport) continue;
-      hunksToLoad[importDeferName[import]] = new Set<OutputUnit>();
-      for (OutputUnit outputUnit in allOutputUnits) {
+      hunksToLoad[importDeferName[import]] = new List<List<OutputUnit>>();
+      int lastNumberOfImports = 0;
+      List<OutputUnit> currentLastList;
+      for (OutputUnit outputUnit in sortedOutputUnits) {
         if (outputUnit == mainOutputUnit) continue;
         if (outputUnit.imports.contains(import)) {
-          hunksToLoad[importDeferName[import]].add(outputUnit);
+          if (outputUnit.imports.length != lastNumberOfImports) {
+            lastNumberOfImports = outputUnit.imports.length;
+            currentLastList = new List<OutputUnit>();
+            hunksToLoad[importDeferName[import]].add(currentLastList);
+          }
+          currentLastList.add(outputUnit);
         }
       }
     }
   }
 
   void onResolutionComplete(FunctionElement main) {
     if (!splitProgram) {
       allOutputUnits.add(mainOutputUnit);
       return;
     }
@@ skipping 118 matching lines @@
     }
     if (splitProgram && compiler.backend is DartBackend) {
       // TODO(sigurdm): Implement deferred loading for dart2dart.
       splitProgram = false;
       compiler.reportInfo(
           lastDeferred,
           MessageKind.DEFERRED_LIBRARY_DART_2_DART);
     }
   }
 }