Cancellable promise

CHANGELOG.md

@@ -1,6 +1,11 @@
 CHANGELOG
 =========
 
+* 2.1.x (xxxx-xx-xx)
+
+  * Introduce new CancellablePromiseInterface implemented by all promises
+  * Add new .cancel() method (part of the CancellablePromiseInterface)
+
 * 2.0.0 (2013-12-10)
 
   New major release. The goal was to streamline the API and to make it more

README.md

@@ -21,6 +21,8 @@ Table of Contents
      * [Deferred::progress()](#deferredprogress)
    * [PromiseInterface](#promiseinterface)
      * [PromiseInterface::then()](#promiseinterfacethen)
+   * [CancellablePromiseInterface](#cancellablepromiseinterface)
+        * [CancellablePromiseInterface::cancel()](#cancellablepromiseinterfacecancel)
    * [Promise](#promise-1)
    * [FulfilledPromise](#fulfilledpromise)
    * [RejectedPromise](#rejectedpromise)
@@ -96,6 +98,9 @@ The `resolve` and `reject` methods control the state of the deferred.
 
 The `progress` method is for progress notification.
 
+The constructor of the `Deferred` accepts an optional `$canceller` argument.
+See [Promise](#promise-1) for more information.
+
 #### Deferred::promise()
 
 ``` php
@@ -197,6 +202,31 @@ the same call to `then()`:
 * [resolve()](#resolve) - Creating a resolved promise
 * [reject()](#reject) - Creating a rejected promise
 
+### CancellablePromiseInterface
+
+A cancellable promise provides a mechanism for consumers to notify the creator
+of the promise that they are not longer interested in the result of an
+operation.
+
+#### CancellablePromiseInterface::cancel()
+
+``` php
+$promise->cancel();
+```
+
+The `cancel()` method notifies the creator of the promise that there is no
+further interest in the results of the operation.
+
+Once a promise is settled (either fulfilled or rejected), calling `cancel()` on
+a promise has no effect.
+
+#### Implementations
+
+* [Promise](#promise-1)
+* [FulfilledPromise](#fulfilledpromise)
+* [RejectedPromise](#rejectedpromise)
+* [LazyPromise](#lazypromise)
+
 ### Promise
 
 Creates a promise whose state is controlled by the functions passed to
@@ -214,11 +244,17 @@ $resolver = function (callable $resolve, callable $reject, callable $progress) {
     // or $progress($progressNotification);
 };
 
-$promise = new React\Promise\Promise($resolver);
+$canceller = function (callable $resolve, callable $reject, callable $progress) {
+    // Cancel/abort any running operations like network connections, streams etc.
+
+    $reject(new \Exception('Promise cancelled'));
+};
+
+$promise = new React\Promise\Promise($resolver, $canceller);
 ```
 
-The promise constructor receives a resolver function which will be called
-with 3 arguments:
+The promise constructor receives a resolver function and an optional canceller
+function which both will be called with 3 arguments:
 
   * `$resolve($value)` - Primary function that seals the fate of the
     returned promise. Accepts either a non-promise value, or another promise.
@@ -228,9 +264,11 @@ with 3 arguments:
   * `$reject($reason)` - Function that rejects the promise.
   * `$progress($update)` - Function that issues progress events for the promise.
 
-If the resolver throws an exception, the promise will be rejected with that
-thrown exception as the rejection reason.
+If the resolver or canceller throw an exception, the promise will be rejected
+with that thrown exception as the rejection reason.
 
+The resolver function will be called immediately, the canceller function only
+once all consumers called the `cancel()` method of the promise.
 
 ### FulfilledPromise
 

src/CancellablePromiseInterface.php

@@ -0,0 +1,11 @@
+<?php
+
+namespace React\Promise;
+
+interface CancellablePromiseInterface extends PromiseInterface
+{
+    /**
+     * @return void
+     */
+    public function cancel();
+}

src/Deferred.php

@@ -8,6 +8,12 @@ class Deferred implements PromisorInterface
     private $resolveCallback;
     private $rejectCallback;
     private $progressCallback;
+    private $canceller;
+
+    public function __construct(callable $canceller = null)
+    {
+        $this->canceller = $canceller;
+    }
 
     public function promise()
     {
@@ -16,7 +22,7 @@ public function promise()
                 $this->resolveCallback  = $resolve;
                 $this->rejectCallback   = $reject;
                 $this->progressCallback = $progress;
-            });
+            }, $this->canceller);
         }
 
         return $this->promise;

src/FulfilledPromise.php

@@ -2,7 +2,7 @@
 
 namespace React\Promise;
 
-class FulfilledPromise implements PromiseInterface
+class FulfilledPromise implements CancellablePromiseInterface
 {
     private $value;
 
@@ -29,4 +29,8 @@ public function then(callable $onFulfilled = null, callable $onRejected = null,
             return new RejectedPromise($exception);
         }
     }
+
+    public function cancel()
+    {
+    }
 }

src/LazyPromise.php

@@ -2,7 +2,7 @@
 
 namespace React\Promise;
 
-class LazyPromise implements PromiseInterface
+class LazyPromise implements CancellablePromiseInterface
 {
     private $factory;
     private $promise;
@@ -13,6 +13,16 @@ public function __construct(callable $factory)
     }
 
     public function then(callable $onFulfilled = null, callable $onRejected = null, callable $onProgress = null)
+    {
+        return $this->promise()->then($onFulfilled, $onRejected, $onProgress);
+    }
+
+    public function cancel()
+    {
+        return $this->promise()->cancel();
+    }
+
+    private function promise()
     {
         if (null === $this->promise) {
             try {
@@ -22,6 +32,6 @@ public function then(callable $onFulfilled = null, callable $onRejected = null,
             }
         }
 
-        return $this->promise->then($onFulfilled, $onRejected, $onProgress);
+        return $this->promise;
     }
 }

src/Promise.php

@@ -2,30 +2,21 @@
 
 namespace React\Promise;
 
-class Promise implements PromiseInterface
+class Promise implements CancellablePromiseInterface
 {
+    private $canceller;
     private $result;
 
     private $handlers = [];
     private $progressHandlers = [];
 
-    public function __construct(callable $resolver)
+    private $requiredCancelRequests = 0;
+    private $cancelRequests = 0;
+
+    public function __construct(callable $resolver, callable $canceller = null)
     {
-        try {
-            $resolver(
-                function ($value = null) {
-                    $this->resolve($value);
-                },
-                function ($reason = null) {
-                    $this->reject($reason);
-                },
-                function ($update = null) {
-                    $this->progress($update);
-                }
-            );
-        } catch (\Exception $e) {
-            $this->reject($e);
-        }
+        $this->canceller = $canceller;
+        $this->call($resolver);
     }
 
     public function then(callable $onFulfilled = null, callable $onRejected = null, callable $onProgress = null)
@@ -34,7 +25,28 @@ public function then(callable $onFulfilled = null, callable $onRejected = null,
             return $this->result->then($onFulfilled, $onRejected, $onProgress);
         }
 
-        return new static($this->resolver($onFulfilled, $onRejected, $onProgress));
+        if (null === $this->canceller) {
+            return new static($this->resolver($onFulfilled, $onRejected, $onProgress));
+        }
+
+        $this->requiredCancelRequests++;
+
+        return new static($this->resolver($onFulfilled, $onRejected, $onProgress), function ($resolve, $reject, $progress) {
+            if (++$this->cancelRequests < $this->requiredCancelRequests) {
+                return;
+            }
+
+            $this->cancel();
+        });
+    }
+
+    public function cancel()
+    {
+        if (null === $this->canceller || null !== $this->result) {
+            return;
+        }
+
+        $this->call($this->canceller);
     }
 
     private function resolver(callable $onFulfilled = null, callable $onRejected = null, callable $onProgress = null)
@@ -101,4 +113,23 @@ private function settle(PromiseInterface $result)
 
         $this->result = $result;
     }
+
+    private function call(callable $callback)
+    {
+        try {
+            $callback(
+                function ($value = null) {
+                    $this->resolve($value);
+                },
+                function ($reason = null) {
+                    $this->reject($reason);
+                },
+                function ($update = null) {
+                    $this->progress($update);
+                }
+            );
+        } catch (\Exception $e) {
+            $this->reject($e);
+        }
+    }
 }

src/RejectedPromise.php

@@ -2,7 +2,7 @@
 
 namespace React\Promise;
 
-class RejectedPromise implements PromiseInterface
+class RejectedPromise implements CancellablePromiseInterface
 {
     private $reason;
 
@@ -27,4 +27,8 @@ public function then(callable $onFulfilled = null, callable $onRejected = null,
             return new RejectedPromise($exception);
         }
     }
+
+    public function cancel()
+    {
+    }
 }

tests/DeferredTest.php

@@ -8,9 +8,9 @@ class DeferredTest extends TestCase
 {
     use PromiseTest\FullTestTrait;
 
-    public function getPromiseTestAdapter()
+    public function getPromiseTestAdapter(callable $canceller = null)
     {
-        $d = new Deferred();
+        $d = new Deferred($canceller);
 
         return new CallbackPromiseAdapter([
             'promise'  => [$d, 'promise'],

tests/FulfilledPromiseTest.php

@@ -9,7 +9,7 @@ class FulfilledPromiseTest extends TestCase
     use PromiseTest\PromiseSettledTestTrait,
         PromiseTest\PromiseFulfilledTestTrait;
 
-    public function getPromiseTestAdapter()
+    public function getPromiseTestAdapter(callable $canceller = null)
     {
         $promise = null;
 

tests/LazyPromiseTest.php

@@ -8,9 +8,9 @@ class LazyPromiseTest extends TestCase
 {
     use PromiseTest\FullTestTrait;
 
-    public function getPromiseTestAdapter()
+    public function getPromiseTestAdapter(callable $canceller = null)
     {
-        $d = new Deferred();
+        $d = new Deferred($canceller);
 
         $factory = function () use ($d) {
             return $d->promise();

tests/PromiseTest.php

@@ -8,15 +8,15 @@ class PromiseTest extends TestCase
 {
     use PromiseTest\FullTestTrait;
 
-    public function getPromiseTestAdapter()
+    public function getPromiseTestAdapter(callable $canceller = null)
     {
         $resolveCallback = $rejectCallback = $progressCallback = null;
 
         $promise = new Promise(function ($resolve, $reject, $progress) use (&$resolveCallback, &$rejectCallback, &$progressCallback) {
             $resolveCallback  = $resolve;
             $rejectCallback   = $reject;
             $progressCallback = $progress;
-        });
+        }, $canceller);
 
         return new CallbackPromiseAdapter([
             'promise' => function () use ($promise) {