Work around possible cyclic garbage references in Exception trace

Author: clue

src/DnsConnector.php

@@ -104,6 +104,10 @@ function ($_, $reject) use (&$promise, &$resolved, $uri) {
 
                 // (try to) cancel pending DNS lookup / connection attempt
                 if ($promise instanceof CancellablePromiseInterface) {
+                    // overwrite callback arguments for PHP7+ only, so they do not show
+                    // up in the Exception trace and do not cause a possible cyclic reference.
+                    $_ = $reject = null;
+
                     $promise->cancel();
                     $promise = null;
                 }

tests/DnsConnectorTest.php

@@ -242,6 +242,34 @@ public function testRejectionAfterDnsLookupShouldNotCreateAnyGarbageReferences()
         $this->assertEquals(0, gc_collect_cycles());
     }
 
+    /**
+     * @requires PHP 7
+     */
+    public function testRejectionAfterDnsLookupShouldNotCreateAnyGarbageReferencesAgain()
+    {
+        if (class_exists('React\Promise\When')) {
+            $this->markTestSkipped('Not supported on legacy Promise v1 API');
+        }
+
+        gc_collect_cycles();
+
+        $dns = new Deferred();
+        $this->resolver->expects($this->once())->method('resolve')->with($this->equalTo('example.com'))->willReturn($dns->promise());
+
+        $tcp = new Deferred();
+        $dns->promise()->then(function () use ($tcp) {
+            $tcp->reject(new \RuntimeException('Connection failed'));
+        });
+        $this->tcp->expects($this->once())->method('connect')->with($this->equalTo('1.2.3.4:80?hostname=example.com'))->willReturn($tcp->promise());
+
+        $promise = $this->connector->connect('example.com:80');
+        $dns->resolve('1.2.3.4');
+
+        unset($promise, $dns, $tcp);
+
+        $this->assertEquals(0, gc_collect_cycles());
+    }
+
     /**
      * @requires PHP 7
      */
@@ -289,7 +317,7 @@ public function testCancelDuringTcpConnectionShouldNotCreateAnyGarbageReferences
         $dns->resolve('1.2.3.4');
 
         $promise->cancel();
-        unset($promise, $dns);
+        unset($promise, $dns, $tcp);
 
         $this->assertEquals(0, gc_collect_cycles());
     }

tests/IntegrationTest.php

@@ -184,7 +184,7 @@ function ($e) use (&$wait) {
     /**
      * @requires PHP 7
      */
-    public function testWaitingForConnectionTimeoutShouldNotCreateAnyGarbageReferences()
+    public function testWaitingForConnectionTimeoutDuringDnsLookupShouldNotCreateAnyGarbageReferences()
     {
         if (class_exists('React\Promise\When')) {
             $this->markTestSkipped('Not supported on legacy Promise v1 API');
@@ -217,6 +217,42 @@ function ($e) use (&$wait) {
         $this->assertEquals(0, gc_collect_cycles());
     }
 
+    /**
+     * @requires PHP 7
+     */
+    public function testWaitingForConnectionTimeoutDuringTcpConnectionShouldNotCreateAnyGarbageReferences()
+    {
+        if (class_exists('React\Promise\When')) {
+            $this->markTestSkipped('Not supported on legacy Promise v1 API');
+        }
+
+        $loop = Factory::create();
+        $connector = new Connector($loop, array('timeout' => 0.000001));
+
+        gc_collect_cycles();
+
+        $wait = true;
+        $promise = $connector->connect('8.8.8.8:53')->then(
+            null,
+            function ($e) use (&$wait) {
+                $wait = false;
+                throw $e;
+            }
+        );
+
+        // run loop for short period to ensure we detect connection timeout error
+        Block\sleep(0.01, $loop);
+        if ($wait) {
+            Block\sleep(0.2, $loop);
+            if ($wait) {
+                $this->fail('Connection attempt did not fail');
+            }
+        }
+        unset($promise);
+
+        $this->assertEquals(0, gc_collect_cycles());
+    }
+
     public function testWaitingForInvalidDnsConnectionShouldNotCreateAnyGarbageReferences()
     {
         if (class_exists('React\Promise\When')) {