First pass at asynchronous input loading in dart2js.

sdk/lib/_internal/compiler/implementation/library_loader.dart

 // 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.
 
 part of dart2js;
 
 /**
  * [CompilerTask] for loading libraries and setting up the import/export scopes.
  *
  * The library loader uses four different kinds of URIs in different parts of
@@ skipping 95 matching lines @@
    *
    * If the library is not already loaded, the method creates the
    * [LibraryElement] for the library and computes the import/export scope,
    * loading and computing the import/export scopes of all required libraries in
    * the process. The method handles cyclic dependency between libraries.
    *
    * This is the main entry point for [LibraryLoader].
    */
   // TODO(johnniwinther): Remove [canonicalUri] together with
   // [Compiler.scanBuiltinLibrary].
-  LibraryElement loadLibrary(Uri resolvedUri, Node node, Uri canonicalUri);
+  Future<LibraryElement> loadLibrary(Uri resolvedUri, Node node,
+                                     Uri canonicalUri);
 
   // TODO(johnniwinther): Remove this when patches don't need special parsing.
-  void registerLibraryFromTag(LibraryDependencyHandler handler,
-                              LibraryElement library,
-                              LibraryDependency tag);
+  Future registerLibraryFromTag(LibraryDependencyHandler handler,
+                                LibraryElement library,
+                                LibraryDependency tag);
 
   /**
    * Adds the elements in the export scope of [importedLibrary] to the import
    * scope of [importingLibrary].
    */
   // TODO(johnniwinther): Move handling of 'js_helper' to the library loader
   // to remove this method from the [LibraryLoader] interface.
   void importLibrary(LibraryElement importingLibrary,
                      LibraryElement importedLibrary,
                      Import tag);
@@ skipping 87 matching lines @@
  */
 class LibraryLoaderTask extends LibraryLoader {
   LibraryLoaderTask(Compiler compiler) : super(compiler);
   String get name => 'LibraryLoader';
 
   final Map<String, LibraryElement> libraryNames =
       new LinkedHashMap<String, LibraryElement>();
 
   LibraryDependencyHandler currentHandler;
 
-  LibraryElement loadLibrary(Uri resolvedUri, Node node, Uri canonicalUri) {
-    return measure(() {
+  Future<LibraryElement> loadLibrary(Uri resolvedUri, Node node, Uri canonicalUri) {

[ahe, 2013/06/26 07:02:00]

Long line.

[Bob Nystrom, 2013/06/27 00:38:18]

Done.

+    return measureAsync(() {

[ahe, 2013/06/26 07:02:00]

I think this should be measure

[Bob Nystrom, 2013/06/27 00:38:18]

Done.

       assert(currentHandler == null);
       currentHandler = new LibraryDependencyHandler(compiler);
-      LibraryElement library =
-          createLibrary(currentHandler, null, resolvedUri, node, canonicalUri);
-      currentHandler.computeExports();
-      currentHandler = null;
-      return library;
+      return createLibrary(currentHandler, null, resolvedUri, node, canonicalUri).then((library) {

[Bob Nystrom, 2013/06/26 01:03:24]

I'll fix these long lines.

[ahe, 2013/06/26 07:02:00]

An then wrap this is in measure as well.

[ahe, 2013/06/26 07:02:00]

Please restore the type of "library".

[Bob Nystrom, 2013/06/27 00:38:18]

Done.

[Bob Nystrom, 2013/06/27 00:38:18]

Done.

+        currentHandler.computeExports();
+        currentHandler = null;
+        return library;
+      });
     });
   }
 
   /**
    * Processes the library tags in [library].
    *
    * The imported/exported libraries are loaded and processed recursively but
    * the import/export scopes are not set up.
    */
-  void processLibraryTags(LibraryDependencyHandler handler,
+  Future processLibraryTags(LibraryDependencyHandler handler,
                           LibraryElement library) {
     int tagState = TagState.NO_TAG_SEEN;
 
     /**
      * If [value] is less than [tagState] complain and return
      * [tagState]. Otherwise return the new value for [tagState]
      * (transition function for state machine).
      */
     int checkTag(int value, LibraryTag tag) {
       if (tagState > value) {
         compiler.reportError(tag, 'out of order');
         return tagState;
       }
       return TagState.NEXT[value];
     }
 
     bool importsDartCore = false;
     var libraryDependencies = new LinkBuilder<LibraryDependency>();
     Uri base = library.entryCompilationUnit.script.uri;
-    for (LibraryTag tag in library.tags.reverse()) {
+
+    return Future.forEach(library.tags.reverse(), (tag) {

[ahe, 2013/06/26 07:02:00]

I need to figure out what this does.

[Bob Nystrom, 2013/06/27 00:38:18]

It should be semantically equivalent to the previous code, just async.
Future.forEach takes a collection and a callback. For each item in the
collection it invokes the callback and passes in the item. The callback is
expected to return a future. It then waits until that future completes before
advancing to the next item.

It's basically a sequential wait. Where Future.wait() waits for all futures in
parallel, .forEach() runs them in series.

       if (tag.isImport) {
         Import import = tag;
         tagState = checkTag(TagState.IMPORT_OR_EXPORT, import);
         if (import.uri.dartString.slowToString() == 'dart:core') {
           importsDartCore = true;
         }
         libraryDependencies.addLast(import);
       } else if (tag.isExport) {
         tagState = checkTag(TagState.IMPORT_OR_EXPORT, tag);
         libraryDependencies.addLast(tag);
       } else if (tag.isLibraryName) {
         tagState = checkTag(TagState.LIBRARY, tag);
         if (library.libraryTag != null) {
           compiler.cancel("duplicated library declaration", node: tag);
         } else {
           library.libraryTag = tag;
         }
         checkDuplicatedLibraryName(library);
       } else if (tag.isPart) {
         Part part = tag;
         StringNode uri = part.uri;
         Uri resolvedUri = base.resolve(uri.dartString.slowToString());
         tagState = checkTag(TagState.SOURCE, part);
-        scanPart(part, resolvedUri, library);
+        return scanPart(part, resolvedUri, library);
       } else {
         compiler.internalError("Unhandled library tag.", node: tag);
       }
-    }
-
-    // Apply patch, if any.
-    if (library.isPlatformLibrary) {
-      patchDartLibrary(handler, library, library.canonicalUri.path);
-    }
-
-    // Import dart:core if not already imported.
-    if (!importsDartCore && !isDartCore(library.canonicalUri)) {
-      handler.registerDependency(library, null, loadCoreLibrary(handler));
-    }
-
-    for (LibraryDependency tag in libraryDependencies.toLink()) {
-      registerLibraryFromTag(handler, library, tag);
-    }
+    }).then((_) {
+      // Apply patch, if any.
+      if (library.isPlatformLibrary) {
+        return patchDartLibrary(handler, library, library.canonicalUri.path);
+      }
+    }).then((_) {
+      // Import dart:core if not already imported.
+      if (!importsDartCore && !isDartCore(library.canonicalUri)) {
+        return loadCoreLibrary(handler).then((coreLibrary) {
+          handler.registerDependency(library, null, coreLibrary);
+        });
+      }
+    }).then((_) {
+      return Future.forEach(libraryDependencies.toLink(), (tag) {
+        return registerLibraryFromTag(handler, library, tag);
+      });
+    });
   }
 
   void checkDuplicatedLibraryName(LibraryElement library) {
     LibraryName tag = library.libraryTag;
     if (tag != null) {
       String name = library.getLibraryOrScriptName();
       LibraryElement existing =
           libraryNames.putIfAbsent(name, () => library);
       if (!identical(existing, library)) {
         Uri uri = library.entryCompilationUnit.script.uri;
         compiler.reportMessage(
             compiler.spanFromSpannable(tag.name, uri),
             MessageKind.DUPLICATED_LIBRARY_NAME.error({'libraryName': name}),
             api.Diagnostic.WARNING);
         Uri existingUri = existing.entryCompilationUnit.script.uri;
         compiler.reportMessage(
             compiler.spanFromSpannable(existing.libraryTag.name, existingUri),
             MessageKind.DUPLICATED_LIBRARY_NAME.error({'libraryName': name}),
             api.Diagnostic.WARNING);
       }
     }
   }
 
   bool isDartCore(Uri uri) => uri.scheme == "dart" && uri.path == "core";
 
   /**
    * Lazily loads and returns the [LibraryElement] for the dart:core library.
    */
-  LibraryElement loadCoreLibrary(LibraryDependencyHandler handler) {
-    if (compiler.coreLibrary == null) {
-      Uri coreUri = new Uri(scheme: 'dart', path: 'core');
-      compiler.coreLibrary
-          = createLibrary(handler, null, coreUri, null, coreUri);
+  Future<LibraryElement> loadCoreLibrary(LibraryDependencyHandler handler) {
+    if (compiler.coreLibrary != null) {
+      return new Future.value(compiler.coreLibrary);
     }
-    return compiler.coreLibrary;
+
+    Uri coreUri = new Uri(scheme: 'dart', path: 'core');
+    return createLibrary(handler, null, coreUri, null, coreUri).then((library) {
+      compiler.coreLibrary = library;
+      return library;
+    });
   }
 
-  void patchDartLibrary(LibraryDependencyHandler handler,
+  Future patchDartLibrary(LibraryDependencyHandler handler,
                         LibraryElement library, String dartLibraryPath) {
-    if (library.isPatched) return;
+    if (library.isPatched) return new Future.value();
     Uri patchUri = compiler.resolvePatchUri(dartLibraryPath);
-    if (patchUri != null) {
-      compiler.patchParser.patchLibrary(handler, patchUri, library);
-    }
+    if (patchUri == null) return new Future.value();
+
+    return compiler.patchParser.patchLibrary(handler, patchUri, library);
   }
 
   /**
    * Handle a part tag in the scope of [library]. The [resolvedUri] given is
    * used as is, any URI resolution should be done beforehand.
    */
-  void scanPart(Part part, Uri resolvedUri, LibraryElement library) {
+  Future scanPart(Part part, Uri resolvedUri, LibraryElement library) {
     if (!resolvedUri.isAbsolute) throw new ArgumentError(resolvedUri);
     Uri readableUri = compiler.translateResolvedUri(library, resolvedUri, part);
-    Script sourceScript = compiler.readScript(readableUri, part);
-    CompilationUnitElement unit =
-        new CompilationUnitElementX(sourceScript, library);
-    compiler.withCurrentElement(unit, () {
-      compiler.scanner.scan(unit);
-      if (unit.partTag == null) {
-        bool wasDiagnosticEmitted = false;
-        compiler.withCurrentElement(library, () {
-          wasDiagnosticEmitted =
-              compiler.onDeprecatedFeature(part, 'missing part-of tag');
-        });
-        if (wasDiagnosticEmitted) {
-          compiler.reportMessage(
-              compiler.spanFromElement(unit),
-              MessageKind.MISSING_PART_OF_TAG.error(),
-              api.Diagnostic.INFO);
+    return compiler.readScript(readableUri, part).then((sourceScript) {
+      CompilationUnitElement unit =
+          new CompilationUnitElementX(sourceScript, library);
+      compiler.withCurrentElement(unit, () {
+        compiler.scanner.scan(unit);
+        if (unit.partTag == null) {
+          bool wasDiagnosticEmitted = false;
+          compiler.withCurrentElement(library, () {
+            wasDiagnosticEmitted =
+                compiler.onDeprecatedFeature(part, 'missing part-of tag');
+          });
+          if (wasDiagnosticEmitted) {
+            compiler.reportMessage(
+                compiler.spanFromElement(unit),
+                MessageKind.MISSING_PART_OF_TAG.error(),
+                api.Diagnostic.INFO);
+          }
         }
-      }
+      });
     });
   }
 
   /**
    * Handle an import/export tag by loading the referenced library and
    * registering its dependency in [handler] for the computation of the import/
    * export scope.
    */
-  void registerLibraryFromTag(LibraryDependencyHandler handler,
+  Future registerLibraryFromTag(LibraryDependencyHandler handler,
                               LibraryElement library,
                               LibraryDependency tag) {
     Uri base = library.entryCompilationUnit.script.uri;
     Uri resolvedUri = base.resolve(tag.uri.dartString.slowToString());
-    LibraryElement loadedLibrary =
-        createLibrary(handler, library, resolvedUri, tag.uri, resolvedUri);
-    handler.registerDependency(library, tag, loadedLibrary);
-
-    if (!loadedLibrary.hasLibraryName()) {
-      compiler.withCurrentElement(library, () {
-        compiler.reportError(tag == null ? null : tag.uri,
-            'no library name found in ${loadedLibrary.canonicalUri}');
-      });
-    }
+    return createLibrary(handler, library, resolvedUri, tag.uri, resolvedUri)
+        .then((loadedLibrary) {
+      handler.registerDependency(library, tag, loadedLibrary);
+      if (!loadedLibrary.hasLibraryName()) {
+        compiler.withCurrentElement(library, () {
+          compiler.reportError(tag == null ? null : tag.uri,
+              'no library name found in ${loadedLibrary.canonicalUri}');
+        });
+      }
+    });
   }
 
   /**
    * Create (or reuse) a library element for the library specified by the
    * [resolvedUri].
    *
    * If a new library is created, the [handler] is notified.
    */
   // TODO(johnniwinther): Remove [canonicalUri] and make [resolvedUri] the
   // canonical uri when [Compiler.scanBuiltinLibrary] is removed.
-  LibraryElement createLibrary(LibraryDependencyHandler handler,
+  Future<LibraryElement> createLibrary(LibraryDependencyHandler handler,
                                LibraryElement importingLibrary,
                                Uri resolvedUri, Node node, Uri canonicalUri) {
-    bool newLibrary = false;
     Uri readableUri =
         compiler.translateResolvedUri(importingLibrary, resolvedUri, node);
     if (readableUri == null) return null;
-    LibraryElement createLibrary() {
-      newLibrary = true;
-      Script script = compiler.readScript(readableUri, node);
+
+    if (canonicalUri != null) {
+      LibraryElement library = compiler.libraries[canonicalUri.toString()];
+      if (library != null) {
+        return new Future.value(library);
+      }
+    }
+
+    return compiler.readScript(readableUri, node).then((script) {
       LibraryElement element = new LibraryElementX(script, canonicalUri);
       handler.registerNewLibrary(element);
       native.maybeEnableNative(compiler, element);
-      return element;
-    }
-    LibraryElement library;
-    if (canonicalUri == null) {
-      library = createLibrary();
-    } else {
-      library = compiler.libraries.putIfAbsent(canonicalUri.toString(),
-                                               createLibrary);
-    }
-    if (newLibrary) {
-      compiler.withCurrentElement(library, () {
-        compiler.scanner.scanLibrary(library);
-        processLibraryTags(handler, library);
-        handler.registerLibraryExports(library);
-        compiler.onLibraryScanned(library, resolvedUri);
+      compiler.libraries[canonicalUri.toString()] = element;
+      return compiler.withCurrentElement(element, () {
+        compiler.scanner.scanLibrary(element);
+        return processLibraryTags(handler, element);
+      }).then((_) {
+        compiler.withCurrentElement(element, () {
+          handler.registerLibraryExports(element);
+          compiler.onLibraryScanned(element, resolvedUri);
+        });
+        return element;
       });
-    }
-    return library;
+    });
   }
 
   // TODO(johnniwinther): Remove this method when 'js_helper' is handled by
   // [LibraryLoaderTask].
   void importLibrary(LibraryElement importingLibrary,
                      LibraryElement importedLibrary,
                      Import tag) {
     new ImportLink(tag, importedLibrary).importLibrary(compiler,
                                                        importingLibrary);
   }
@@ skipping 376 matching lines @@
   }
 
   /**
    * Registers all top-level entities of [library] as starting point for the
    * fixed-point computation of the import/export scopes.
    */
   void registerLibraryExports(LibraryElement library) {
     nodeMap[library].registerInitialExports();
   }
 }