From 6d2753441b869597bc4c05f0f54ac1750c75d53e Mon Sep 17 00:00:00 2001
From: Brian Cavalier <brian@hovercraftstudios.com>
Date: Fri, 19 Dec 2014 08:04:56 -0500
Subject: [PATCH] Initial prototype for AbortablePromise

---
 lib/makeAbortablePromise.js | 103 ++++++++++++++++++++++++++++++++++++
 lib/makePromise.js          |  14 ++---
 2 files changed, 111 insertions(+), 6 deletions(-)
 create mode 100644 lib/makeAbortablePromise.js

diff --git a/lib/makeAbortablePromise.js b/lib/makeAbortablePromise.js
new file mode 100644
index 00000000..42ba5325
--- /dev/null
+++ b/lib/makeAbortablePromise.js
@@ -0,0 +1,103 @@
+/** @license MIT License (c) copyright 2010-2014 original author or authors */
+/** @author Brian Cavalier */
+/** @author John Hann */
+
+(function(define) { 'use strict';
+define(function() {
+
+	return function makeAbortablePromise(Promise) {
+
+		function AbortablePromise(resolver) {
+			Promise.call(this, makeAbortableResolver(resolver, this));
+		}
+
+		AbortablePromise.prototype = Object.create(Promise.prototype);
+
+		// Set constructor so that Promise.prototype.then will work
+		AbortablePromise.prototype.constructor = AbortablePromise;
+
+		AbortablePromise.prototype.then = function(f, r, p) {
+			var child = Promise.prototype.then.call(this, f, r, p);
+
+			// Propagate abort to child via handler
+			child._handler.abort = this._handler.abort;
+
+			return child;
+		};
+
+		AbortablePromise.prototype.abort = function() {
+			var handler = this._handler;
+
+			if (typeof handler.abort !== 'function') {
+				return;
+			}
+
+			// Detach abort so it can only be called once
+			var fn = handler.abort;
+			handler.abort = null;
+
+			try {
+				// aborter may return a promise to control the outcome of
+				// the abort process.
+				var abortResult = fn.apply(void 0, arguments);
+				handler.resolve(abortResult);
+
+				// Ensure return value is always a promise, specifically a
+				// non-abortable promise
+				return Promise.resolve(abortResult);
+			} catch (e) {
+				console.error(e.stack);
+				handler.reject(e);
+			}
+		};
+
+		function makeAbortableResolver(task, abortablePromise) {
+			return function() {
+				runAbortableTask(task, abortablePromise._handler);
+			};
+		}
+
+		function runAbortableTask(task, handler) {
+			// Make rejecting be the default abort behavior.
+			handler.abort = defaultAbort;
+
+			// Resolver may return an aborter function
+			var result = task(abortableResolve, abortableReject);
+
+			// If it did, stash it on the handler
+			if(typeof result === 'function') {
+				handler.abort = result;
+			}
+
+			function abortableResolve(x) {
+				// If x is also an abortable promise, propagate its abort function
+				// to handler.
+				handler.abort = getAbort(x);
+				handler.resolve(x);
+			}
+
+			function abortableReject(e) {
+				// Always disable abort upon reject
+				handler.abort = null;
+				handler.reject(e);
+			}
+
+			function defaultAbort(x) {
+				handler.reject(x);
+			}
+		}
+
+		return AbortablePromise;
+	};
+
+	function getAbort (x) {
+		// Make a reasonable attempt to recognize abortable thenables
+		return maybeThenable(x) ? x.abort : null;
+	}
+
+	function maybeThenable(x) {
+		return (typeof x === 'object' || typeof x === 'function') && x !== null;
+	}
+
+});
+}(typeof define === 'function' && define.amd ? define : function(factory) { module.exports = factory(); }));
diff --git a/lib/makePromise.js b/lib/makePromise.js
index 56a09f85..2a497ad0 100644
--- a/lib/makePromise.js
+++ b/lib/makePromise.js
@@ -23,25 +23,27 @@ define(function() {
 		 * @name Promise
 		 */
 		function Promise(resolver, handler) {
-			this._handler = resolver === Handler ? handler : init(resolver);
+			if(resolver === Handler) {
+				this._handler = handler;
+			} else {
+				this._handler = new Pending();
+				init(resolver, this._handler);
+			}
 		}
 
 		/**
 		 * Run the supplied resolver
 		 * @param resolver
+		 * @param handler
 		 * @returns {Pending}
 		 */
-		function init(resolver) {
-			var handler = new Pending();
-
+		function init(resolver, handler) {
 			try {
 				resolver(promiseResolve, promiseReject, promiseNotify);
 			} catch (e) {
 				promiseReject(e);
 			}
 
-			return handler;
-
 			/**
 			 * Transition from pre-resolution state to post-resolution state, notifying
 			 * all listeners of the ultimate fulfillment or rejection