Crawler, second version

lib/counter_task.js

+let {Logger} = require( "logger" );
+
+/**
+ * This task just counts.
+ *
+ * @param count
+ *      The number of iterations.
+ * @param count_notifier
+ *      The count notifier is called once at each iteration with this current loop counter.
+ * @param completion_notifier
+ *      The completion notifier is called when the task is finished. Because a long running task does not run
+ *      synchronously, we need some kind of notification system.
+ * @param {Boolean} [use_slow_version=true]
+ */
+var Counting_Task = exports.Counting_Task = function( count, count_notifier, completion_notifier, variant )
+{
+  this.count = count;
+  this.count_notifier = count_notifier;
+  this.completion_notifier = completion_notifier;
+
+  this.logger = new Logger( "Counting_Task" );
+
+  switch ( variant.type )
+  {
+    case "segmented fast":
+      this.segmented = true;
+      this._dispatch_self = function()
+      {
+        this.thread_manager.currentThread.dispatch( { run: this.land }, Ci.nsIEventTarget.DISPATCH_NORMAL );
+      };
+      /**
+       * Thread manager is used to make counting an asynchronous operation.
+       * @type {nsIThreadManager}
+       */
+      this.thread_manager = Cc["@mozilla.org/thread-manager;1"].createInstance( Ci.nsIThreadManager );
+      break;
+    case "segmented slow":
+      this.segmented = true;
+      this._dispatch_self = function()
+      {
+        this.timer.initWithCallback( this.land.bind( this ), 100, Ci.nsITimer.TYPE_ONE_SHOT );
+      };
+      /**
+       * This task uses a timer to slow down the count in order to provide a simulation of a slow task to exercise
+       * pause-resume functionality.
+       * @type {*}
+       */
+      this.timer = Cc["@mozilla.org/timer;1"].createInstance( Ci.nsITimer );
+      break;
+    case "continuous":
+      this.segmented = false;
+      break;
+    default:
+      throw "Unknown Counting_task variant";
+  }
+  this.logger.make_log()( "using " + variant.type + " variant" );
+};
+
+/**
+ * The generator for the task.
+ *
+ * @param {Function} pause
+ * @param {Function} resume
+ */
+Counting_Task.prototype.generator = function( pause, resume )
+{
+  var log = this.logger.make_log( "task" );
+  log( "begin" );
+
+  /**
+   * Flag indicating if there's a pending asynchronous operation.
+   * @type {Boolean}
+   */
+  var pending = false;
+
+  /**
+   * Internal landing function for segmented variants. Defined here to gain access to the scope variables in the chain
+   * of the present invocation of the function.
+   */
+  this.land = function()
+  {
+    pending = false;
+    resume();
+  };
+
+  var j;
+  for ( j = 0 ; j < this.count ; ++j )
+  {
+    if ( this.segmented && !pending )
+    {
+      this._dispatch_self();
+      pause();
+      pending = true;
+    }
+    /*
+     * The rvalue of a yield statement is the argument to 'send()' called on the generator. The task runner
+     * calls 'send( true )' to indicated cancellation. 'next()' is a synonym for 'send( undefined )'. Thus,
+     * the possible values for 'cancelled' are 'true' and 'undefined'.
+     */
+    var cancelled = yield false;
+    if ( cancelled )
+    {
+      log( "cancelled" );
+      break;
+    }
+    if ( this.count_notifier )
+      this.count_notifier( j );
+  }
+  if ( j == this.count )
+  {
+    // Assert the loop terminated in the 'for' statement, not with a cancellation.
+    log( "finished" )
+  }
+  if ( this.completion_notifier )
+    this.completion_notifier();
+  log( "end" );
+};