Add ServerOperation and queue.

pkg/analysis_server/lib/src/operation/operation.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 operation;
+
+import 'package:analysis_server/src/analysis_server.dart';
+import 'package:analyzer/src/generated/engine.dart' show AnalysisContext;
+
+
+/**
+ * The enumeration [ServerOperationPriority] defines the priority levels used
+ * to organize [ServerOperation]s in an optimal order. A smaller ordinal value
+ * equates to a higher priority.
+ */
+class ServerOperationPriority {
+  final int ordinal;
+  final String name;
+
+  static const int COUNT = 4;
+
+  static const ServerOperationPriority ANALYSIS_CONTINUE = const ServerOperationPriority._(0, "ANALYSIS_CONTINUE");
+  static const ServerOperationPriority ANALYSIS = const ServerOperationPriority._(1, "ANALYSIS");
+  static const ServerOperationPriority SEARCH = const ServerOperationPriority._(2, "SEARCH");
+  static const ServerOperationPriority REFACTORING = const ServerOperationPriority._(3, "REFACTORING");
+
+  @override
+  String toString() => name;
+
+  const ServerOperationPriority._(this.ordinal, this.name);
+}
+
+
+/**
+ * The class [ServerOperation] defines the behavior of objects used to perform
+ * operations on a [AnalysisServer].
+ */
+abstract class ServerOperation {
+  /**
+   * Returns the priority of this operation.
+   */
+  ServerOperationPriority get priority;
+
+  /**
+   * Performs the operation implemented by this operation.
+   */
+  void perform(AnalysisServer server);
+}
+
+
+/**
+ * Instances of [PerformAnalysisOperation] perform a single analysis task.
+ */
+class PerformAnalysisOperation extends ServerOperation {
+  final AnalysisContext context;
+  final bool isContinue;
+
+  PerformAnalysisOperation(this.context, this.isContinue);
+
+  @override
+  ServerOperationPriority get priority {
+    if (isContinue) {
+      return ServerOperationPriority.ANALYSIS_CONTINUE;
+    } else {
+      return ServerOperationPriority.ANALYSIS;
+    }
+  }
+
+  @override
+  void perform(AnalysisServer server) {
+    server.internalPerformAnalysis(context);
+  }
+}