Added support for cancellable promises (#72, reactphp/promise#20)

README.md

@@ -246,11 +246,8 @@ adapted into a [PromiseCoroutine](src/Coroutine/PromiseCoroutine.php) instance a
 the promise has been fulfilled.
 
 If the promise is resolved, the resulting value is returned from the yield statement. If it is rejected, the yield
-statement throws an exception describing the error. **Recoil** does not yet support progress events.
-
-React promises are based on the [Promise/A+](https://github.com/promises-aplus/promises-spec) specification, which does
-not yet define a mechanism for cancellation of pending promises. As such, terminating a coroutine that is waiting on a
-promise simply causes the promise resolution to be ignored.
+statement throws an exception describing the error. If a strand is waiting on the resolution of a cancellable promise,
+and execution of that strand is terminated the promise is cancelled. **Recoil** does not yet support progress events.
 
 The [promise-dns example](examples/promise-dns) demonstrates using the [React DNS component](https://github.com/reactphp/dns),
 a promised-based API, to resolve several domain names concurrently. [This example](examples/promise-dns-react) shows the

composer.json

@@ -26,7 +26,8 @@
         "php": ">=5.5",
         "evenement/evenement": "~2",
         "icecave/repr": "~1",
-        "react/react": "0.4.0|~0.4.2"
+        "react/react": "0.4.0|~0.4.2",
+        "react/promise": "dev-cancellable-promise as 2.9.9"
     },
     "require-dev": {
         "icecave/archer": "~1",

src/Coroutine/PromiseCoroutine.php

@@ -2,9 +2,10 @@
 namespace Recoil\Coroutine;
 
 use Exception;
+use React\Promise\CancellablePromiseInterface;
+use React\Promise\PromiseInterface;
 use Recoil\Coroutine\Exception\PromiseRejectedException;
 use Recoil\Kernel\Strand\StrandInterface;
-use React\Promise\PromiseInterface;
 
 /**
  * A coroutine that resumes when a promise is fulfilled or rejected.
@@ -47,19 +48,15 @@ function ($reason) use ($strand) {
     }
 
     /**
-     * Adapt a promise rejection reason into an exception.
+     * Inform the coroutine that the executing strand is being terminated.
      *
-     * @param mixed $reason
-     *
-     * @return Exception
+     * @param StrandInterface $strand The strand that is executing the coroutine.
      */
-    protected function adaptReasonToException($reason)
+    public function terminate(StrandInterface $strand)
     {
-        if ($reason instanceof Exception) {
-            return $reason;
+        if ($this->promise instanceof CancellablePromiseInterface) {
+            $this->promise->cancel();
         }
-
-        return new PromiseRejectedException($reason);
     }
 
     /**
@@ -74,5 +71,21 @@ public function finalize(StrandInterface $strand)
         $this->promise = null;
     }
 
+    /**
+     * Adapt a promise rejection reason into an exception.
+     *
+     * @param mixed $reason
+     *
+     * @return Exception
+     */
+    protected function adaptReasonToException($reason)
+    {
+        if ($reason instanceof Exception) {
+            return $reason;
+        }
+
+        return new PromiseRejectedException($reason);
+    }
+
     private $promise;
 }