From c2a547bdf84e9ca129193b982aad1d99a72eaa2d Mon Sep 17 00:00:00 2001
From: Marcelo Shima <marceloshima@gmail.com>
Date: Fri, 3 Apr 2020 12:01:35 -0300
Subject: [PATCH] Implement cancellable tasks. (#1204)

---
 lib/index.js | 18 +++++++++++++++++-
 test/base.js | 12 ++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/lib/index.js b/lib/index.js
index 09598a5b..c678a16a 100644
--- a/lib/index.js
+++ b/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') {
diff --git a/test/base.js b/test/base.js
index ec5e20ac..d5a2198e 100644
--- a/test/base.js
+++ b/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()', () => {