Implement cancellable tasks. (#1204)

lib/index.js

@@ -650,11 +650,20 @@ class Generator extends EventEmitter {
  self.emit(`method:${methodName}`);
 
  runAsync(function() {
+ if (task.cancellable && !self._running) {
+ return Promise.resolve();
+ }
+
  self.async = () => this.async();
  self.runningState = { namespace, queueName, methodName };
  return method.apply(self, self.args);
  })()
  .then(function() {
+ if (task.cancellable && !self._running) {
+ completed();
+ return;
+ }
+
  delete self.runningState;
  const eventName = `done$${namespace || 'unknownnamespace'}#${methodName}`;
  debug(`Emiting event ${eventName}`);
@@ -682,6 +691,13 @@ class Generator extends EventEmitter {
  );
  }
 
+ /**
+ * Ignore cancellable tasks.
+ */
+ cancelCancellableTasks() {
+ this._running = false;
+ }
+
  /**
  * Runs the generator, scheduling prototype methods on a run queue. Method names
  * will determine the order each method is run. Methods without special names
@@ -729,7 +745,7 @@ class Generator extends EventEmitter {
  const item = property.value ? property.value : property.get.call(self);
 
  const priority = self._queues[name];
- let taskOptions = { ...priority };
+ let taskOptions = { ...priority, cancellable: true };
 
  // Name points to a function; run it!
  if (typeof item === 'function') {

test/base.js

@@ -497,6 +497,18 @@ describe('Base', () => {
  assert(fs.existsSync(this.testGen.destinationPath('foo.txt')));
  });
  });
+
+ it('can cancel cancellable tasks', function(done) {
+ this.TestGenerator.prototype.cancel = function() {
+ this.cancelCancellableTasks();
+ };
+
+ this.TestGenerator.prototype.throwing = () => {
+ throw new Error('not thrown');
+ };
+
+ this.testGen.run().then(done);
+ });
  });
 
  describe('#argument()', () => {