From 44bc9715d608956c813994d8b1b2198c668a4235 Mon Sep 17 00:00:00 2001
From: Niklas Keller <me@kelunik.com>
Date: Fri, 23 Dec 2016 22:26:05 +0100
Subject: [PATCH] Fix Promise::when invocation order

---
 lib/Internal/Placeholder.php | 39 ++++++++++++++++++------------------
 test/WhenOrderTest.php       | 30 +++++++++++++++++++++++++++
 2 files changed, 50 insertions(+), 19 deletions(-)
 create mode 100644 test/WhenOrderTest.php

diff --git a/lib/Internal/Placeholder.php b/lib/Internal/Placeholder.php
index 2c5a06eb..346a0eae 100644
--- a/lib/Internal/Placeholder.php
+++ b/lib/Internal/Placeholder.php
@@ -17,10 +17,10 @@ trait Placeholder {
 
     /** @var mixed */
     private $result;
-    
+
     /** @var callable|\Amp\Internal\WhenQueue|null */
     private $onResolved;
-    
+
     /**
      * @see \Interop\Async\Promise::when()
      */
@@ -63,27 +63,28 @@ private function resolve($value = null) {
             throw new \Error("Promise has already been resolved");
         }
 
-        $this->resolved = true;
         $this->result = $value;
 
-        if ($this->onResolved === null) {
-            return;
-        }
+        try {
+            while ($this->onResolved !== null) {
+                $onResolved = $this->onResolved;
+                $this->onResolved = null;
 
-        $onResolved = $this->onResolved;
-        $this->onResolved = null;
+                if ($this->result instanceof Promise) {
+                    $this->result->when($onResolved);
+                    return;
+                }
 
-        if ($this->result instanceof Promise) {
-            $this->result->when($onResolved);
-            return;
-        }
-        
-        try {
-            $onResolved(null, $this->result);
-        } catch (\Throwable $exception) {
-            Loop::defer(static function () use ($exception) {
-                throw $exception;
-            });
+                try {
+                    $onResolved(null, $this->result);
+                } catch (\Throwable $exception) {
+                    Loop::defer(static function () use ($exception) {
+                        throw $exception;
+                    });
+                }
+            }
+        } finally {
+            $this->resolved = true;
         }
     }
 
diff --git a/test/WhenOrderTest.php b/test/WhenOrderTest.php
new file mode 100644
index 00000000..9ffea938
--- /dev/null
+++ b/test/WhenOrderTest.php
@@ -0,0 +1,30 @@
+<?php declare(strict_types = 1);
+
+namespace Amp\Test;
+
+use Amp\Deferred;
+
+class WhenOrderTest extends \PHPUnit_Framework_TestCase {
+    public function testWhenOrder() {
+        $this->expectOutputString("1234");
+
+        $deferred = new Deferred;
+        $promise = $deferred->promise();
+
+        $promise->when(function () use ($promise) {
+            $promise->when(function () {
+                printf("%d", 3);
+            });
+            printf("%d", 1);
+        });
+
+        $promise->when(function () use ($promise) {
+            $promise->when(function () {
+                printf("%d", 4);
+            });
+            printf("%d", 2);
+        });
+
+        $deferred->resolve();
+    }
+}