Add better error handling

Author: Maxime Rainville

examples/basic-usage.php

@@ -60,3 +60,11 @@ function () use ($event) {
 $event = new UserCreatedEvent('789', '[email protected]');
 $future = $dispatcher->dispatch($event, new TimeoutCancellation(30));
 EventLoop::run();
+
+// Set up logging for your dispatcher - all errors will be logged to PSR logger
+$dispatcher = new AsyncEventDispatcher(
+    $listenerProvider,
+    function (Throwable $exception) {
+        error_log($exception->getMessage());
+    }
+);

src/AsyncEventDispatcher.php

@@ -7,14 +7,17 @@
 use function Amp\async;
 
 use Amp\Cancellation;
+
 use Amp\Future;
 
 use function Amp\Future\awaitAll;
 
 use Amp\NullCancellation;
+use Closure;
 use Psr\EventDispatcher\EventDispatcherInterface;
 use Psr\EventDispatcher\ListenerProviderInterface;
 use Psr\EventDispatcher\StoppableEventInterface;
+use Throwable;
 
 /**
  * Asynchronous implementation of PSR-14 EventDispatcherInterface using Revolt and AMPHP.
@@ -24,12 +27,22 @@
  */
 class AsyncEventDispatcher implements EventDispatcherInterface
 {
+    /** @var Closure(Throwable): (void) */
+    private Closure $errorHandler;
+
     /**
      * @param ListenerProviderInterface $listenerProvider The provider of event listeners
+     * @param Closure(Throwable): (void) $errorHandler The handler for errors thrown by listeners
      */
     public function __construct(
-        private readonly ListenerProviderInterface $listenerProvider
+        private readonly ListenerProviderInterface $listenerProvider,
+        ?Closure $errorHandler = null
     ) {
+        if ($errorHandler === null) {
+            $this->errorHandler = function (Throwable $exception): void {};
+        } else {
+            $this->errorHandler = $errorHandler;
+        }
     }
 
     /**
@@ -85,7 +98,7 @@ private function dispatchStoppableEvent(
                 // that doesn't mean we want to block other listeners outside this loop.
                 $future = async(function () use ($event, $listener) {
                     $listener($event);
-                });
+                })->catch($this->errorHandler);
 
                 $future->await($cancellation);
 
@@ -120,14 +133,13 @@ private function dispatchNonStoppableEvent(
             foreach ($listeners as $listener) {
                 $futures[] = async(function () use ($event, $listener) {
                     $listener($event);
-                });
+                })->catch($this->errorHandler);
             }
 
-            // Wait for all listeners to complete
+            // Wait for all listeners to complete. This will carry on despite errors.
             awaitAll($futures, $cancellation);
 
             return $event;
         });
     }
-
 }

tests/AsyncEventDispatcherTest.php

@@ -15,8 +15,6 @@
 use ArchiPro\EventDispatcher\Tests\Fixture\TestEvent;
 use Exception;
 use PHPUnit\Framework\TestCase;
-use Revolt\EventLoop;
-
 use Throwable;
 
 /**
@@ -34,18 +32,21 @@ class AsyncEventDispatcherTest extends TestCase
     private ListenerProvider $listenerProvider;
     private AsyncEventDispatcher $dispatcher;
 
+    /** @var array<Throwable> */
+    private array $errors = [];
+
     /**
      * Sets up the test environment before each test.
      */
     protected function setUp(): void
     {
         $this->listenerProvider = new ListenerProvider();
-        $this->dispatcher = new AsyncEventDispatcher($this->listenerProvider);
-
-        EventLoop::setErrorHandler(function (Throwable $err) {
-            throw $err;
-        });
-
+        $this->dispatcher = new AsyncEventDispatcher(
+            $this->listenerProvider,
+            function (Throwable $exception) {
+                $this->errors[] = $exception;
+            }
+        );
     }
 
     /**
@@ -80,6 +81,8 @@ public function testDispatchEventToMultipleListeners(): void
         $this->assertCount(2, $results);
         $this->assertContains('listener1: test data', $results);
         $this->assertContains('listener2: test data', $results);
+
+        $this->assertCount(0, $this->errors, 'No errors are logged');
     }
 
     /**
@@ -103,6 +106,8 @@ public function testSynchronousStoppableEvent(): void
 
         $this->assertCount(1, $results);
         $this->assertEquals(['listener1'], $results);
+
+        $this->assertCount(0, $this->errors, 'No errors are logged');
     }
 
     /**
@@ -114,6 +119,7 @@ public function testNoListenersForEvent(): void
         $dispatchedEvent = $this->dispatcher->dispatch($event);
 
         $this->assertSame($event, $dispatchedEvent->await());
+        $this->assertCount(0, $this->errors, 'No errors are logged');
     }
 
     /**
@@ -158,16 +164,18 @@ public function testDispatchesFailureInOneListenerDoesNotAffectOthers(): void
 
         $futureEvent = $this->dispatcher->dispatch($event);
 
-        $futureEvent = $futureEvent->await();
+        $futureEvent->await();
 
         $this->assertTrue(
-            $futureEvent->calledOnce,
+            $event->calledOnce,
             'The first listener should have been called'
         );
         $this->assertTrue(
-            $futureEvent->calledTwice,
+            $event->calledTwice,
             'The second listener should have been called despite the failure of the first listener'
         );
+
+        $this->assertCount(2, $this->errors, 'Errors are caught for both listeners');
     }
 
     public function testCancellationOfStoppableEvent(): void
@@ -187,6 +195,8 @@ public function testCancellationOfStoppableEvent(): void
         $this->expectException(CancelledException::class);
 
         $this->dispatcher->dispatch($event, $cancellation)->await();
+
+        $this->assertCount(0, $this->errors, 'No errors are caught');
     }
 
     public function testCancellationOfNonStoppableEvent(): void
@@ -206,6 +216,7 @@ public function testCancellationOfNonStoppableEvent(): void
         $this->expectException(CancelledException::class);
 
         $this->dispatcher->dispatch($event, $cancellation)->await();
-    }
 
+        $this->assertCount(0, $this->errors, 'No errors are caught');
+    }
 }