Add ServerOperation and queue.

pkg/analysis_server/lib/src/operation/operation_queue.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.queue;
+
+import 'dart:collection';
+
+import 'package:analysis_server/src/analysis_server.dart';
+import 'package:analysis_server/src/operation/operation.dart';
+
+
+/**
+ * A queue of operations in an [AnalysisServer].
+ */
+class ServerOperationQueue {
+  final List<ServerOperationPriority> _analysisPriorities = [
+      ServerOperationPriority.ANALYSIS_CONTINUE,
+      ServerOperationPriority.ANALYSIS];
+
+  final AnalysisServer _server;
+  final List<Queue<ServerOperation>> _queues = <Queue<ServerOperation>>[];
+
+  ServerOperationQueue(this._server) {
+    for (int i = 0; i < ServerOperationPriority.COUNT; i++) {
+      var queue = new DoubleLinkedQueue<ServerOperation>();
+      _queues.add(queue);
+    }
+  }
+
+  /**
+   * Adds the given operation to this queue. The exact position in the queue
+   * depends on the priority of the given operation relative to the priorities
+   * of the other operations in the queue.
+   */
+   void add(ServerOperation operation) {
+    int queueIndex = operation.priority.ordinal;
+    Queue<ServerOperation> queue = _queues[queueIndex];
+    queue.addLast(operation);
+  }
+
+  /**
+   * Removes all elements in the queue.
+   */
+  void clear() {
+    for (Queue<ServerOperation> queue in _queues) {
+      queue.clear();
+    }
+  }
+
+  /**
+   * Returns `true` if there are no queued [ServerOperation]s.
+   */
+  bool get isEmpty {
+    return _queues.every((queue) => queue.isEmpty);
+  }
+
+  /**
+   * Returns the next operation to perform or `null` if empty.
+   */
+  ServerOperation take() {
+    // try to find a priority analysis operarion
+    for (ServerOperationPriority priority in _analysisPriorities) {
+      Queue<ServerOperation> queue = _queues[priority.ordinal];
+      for (PerformAnalysisOperation operation in queue) {
+        if (_server.isPriorityContext(operation.context)) {
+          queue.remove(operation);
+          return operation;
+        }
+      }
+    }
+    // non-priority operations
+    for (Queue<ServerOperation> queue in _queues) {
+      if (!queue.isEmpty) {
+        return queue.removeFirst();
+      }
+    }
+    // empty
+    return null;
+  }
+}
+