From fcfa37a27be0c66f11c0ecbf6c2d1e18326497cc Mon Sep 17 00:00:00 2001
From: Simon Frings <simon@clue.engineering>
Date: Thu, 24 Feb 2022 11:05:01 +0100
Subject: [PATCH] Only stop loop if a pending promise resolves/rejects

---
 src/functions.php   |  16 +++--
 tests/AwaitTest.php | 143 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 155 insertions(+), 4 deletions(-)

diff --git a/src/functions.php b/src/functions.php
index 0f2ef7e..e4d3fec 100644
--- a/src/functions.php
+++ b/src/functions.php
@@ -54,18 +54,25 @@ function await(PromiseInterface $promise)
     $resolved = null;
     $exception = null;
     $rejected = false;
+    $loopStarted = false;
 
     $promise->then(
-        function ($c) use (&$resolved, &$wait) {
+        function ($c) use (&$resolved, &$wait, &$loopStarted) {
             $resolved = $c;
             $wait = false;
-            Loop::stop();
+
+            if ($loopStarted) {
+                Loop::stop();
+            }
         },
-        function ($error) use (&$exception, &$rejected, &$wait) {
+        function ($error) use (&$exception, &$rejected, &$wait, &$loopStarted) {
             $exception = $error;
             $rejected = true;
             $wait = false;
-            Loop::stop();
+
+            if ($loopStarted) {
+                Loop::stop();
+            }
         }
     );
 
@@ -74,6 +81,7 @@ function ($error) use (&$exception, &$rejected, &$wait) {
     $promise = null;
 
     while ($wait) {
+        $loopStarted = true;
         Loop::run();
     }
 
diff --git a/tests/AwaitTest.php b/tests/AwaitTest.php
index 1acc7e3..9e03be6 100644
--- a/tests/AwaitTest.php
+++ b/tests/AwaitTest.php
@@ -82,6 +82,149 @@ public function testAwaitReturnsValueWhenPromiseIsFulfilledEvenWhenOtherTimerSto
         $this->assertEquals(2, React\Async\await($promise));
     }
 
+    public function testAwaitWithAlreadyFulfilledPromiseWillReturnWithoutRunningLoop()
+    {
+        $now = true;
+
+        Loop::futureTick(function () use (&$now) {
+            $now = false;
+        });
+
+        $promise = new Promise(function ($resolve) {
+            $resolve(42);
+        });
+
+        React\Async\await($promise);
+        $this->assertTrue($now);
+    }
+
+    public function testAwaitWithAlreadyFulfilledPromiseWillReturnWithoutStoppingLoop()
+    {
+        $ticks = 0;
+
+        $promise = new Promise(function ($resolve) {
+            $resolve(42);
+        });
+
+        // Loop will execute this tick first
+        Loop::futureTick(function () use (&$ticks) {
+            ++$ticks;
+            // Loop will execute this tick third
+            Loop::futureTick(function () use (&$ticks) {
+                ++$ticks;
+            });
+        });
+
+        // Loop will execute this tick second
+        Loop::futureTick(function () use (&$promise){
+            // await won't stop the loop if promise already resolved -> third tick will trigger
+            React\Async\await($promise);
+        });
+
+        Loop::run();
+
+        $this->assertEquals(2, $ticks);
+    }
+
+    public function testAwaitWithPendingPromiseThatWillResolveWillStopLoopBeforeLastTimerFinishes()
+    {
+        $promise = new Promise(function ($resolve) {
+            Loop::addTimer(0.02, function () use ($resolve) {
+                $resolve(2);
+            });
+        });
+
+        $ticks = 0;
+
+        // Loop will execute this tick first
+        Loop::futureTick(function () use (&$ticks) {
+            ++$ticks;
+            // This timer will never finish because Loop gets stopped by await
+            // Loop needs to be manually started again to finish this timer
+            Loop::addTimer(0.04, function () use (&$ticks) {
+                ++$ticks;
+            });
+        });
+
+        // await stops the loop when promise resolves after 0.02s
+        Loop::futureTick(function () use (&$promise){
+            React\Async\await($promise);
+        });
+
+        Loop::run();
+
+        // This bahvior exists in v2 & v3 of async, we recommend to use fibers in v4 (PHP>=8.1)
+        $this->assertEquals(1, $ticks);
+    }
+
+    public function testAwaitWithAlreadyRejectedPromiseWillReturnWithoutStoppingLoop()
+    {
+        $ticks = 0;
+
+        $promise = new Promise(function ($_, $reject) {
+            throw new \Exception();
+        });
+
+        // Loop will execute this tick first
+        Loop::futureTick(function () use (&$ticks) {
+            ++$ticks;
+            // Loop will execute this tick third
+            Loop::futureTick(function () use (&$ticks) {
+                ++$ticks;
+            });
+        });
+
+        // Loop will execute this tick second
+        Loop::futureTick(function () use (&$promise){
+            try {
+                // await won't stop the loop if promise already rejected -> third tick will trigger
+                React\Async\await($promise);
+            } catch (\Exception $e) {
+                // no-op
+            }
+        });
+
+        Loop::run();
+
+        $this->assertEquals(2, $ticks);
+    }
+
+    public function testAwaitWithPendingPromiseThatWillRejectWillStopLoopBeforeLastTimerFinishes()
+    {
+        $promise = new Promise(function ($_, $reject) {
+            Loop::addTimer(0.02, function () use (&$reject) {
+                $reject(new \Exception());
+            });
+        });
+
+        $ticks = 0;
+
+        // Loop will execute this tick first
+        Loop::futureTick(function () use (&$ticks) {
+            ++$ticks;
+            // This timer will never finish because Loop gets stopped by await
+            // Loop needs to be manually started again to finish this timer
+            Loop::addTimer(0.04, function () use (&$ticks) {
+                ++$ticks;
+            });
+        });
+
+        // Loop will execute this tick second
+        // await stops the loop when promise rejects after 0.02s
+        Loop::futureTick(function () use (&$promise){
+            try {
+                React\Async\await($promise);
+            } catch (\Exception $e) {
+                // no-op
+            }
+        });
+
+        Loop::run();
+
+        // This bahvior exists in v2 & v3 of async, we recommend to use fibers in v4 (PHP>=8.1)
+        $this->assertEquals(1, $ticks);
+    }
+
     public function testAwaitShouldNotCreateAnyGarbageReferencesForResolvedPromise()
     {
         if (class_exists('React\Promise\When') && PHP_VERSION_ID >= 50400) {