ACP2E-4040: 500 error occurs on frontend, due to incorrect layout structure is cached in layout

Author: abukatar

lib/internal/Magento/Framework/View/Layout.php

@@ -22,6 +22,7 @@
 use Magento\Framework\View\Layout\Reader\ContextFactory;
 use Magento\Framework\View\Layout\ReaderPool;
 use Psr\Log\LoggerInterface as Logger;
+use Magento\Framework\View\Layout\Reader\Context;
 
 /**
  * Layout model
@@ -375,13 +376,41 @@ public function generateElements()
         );
 
         \Magento\Framework\Profiler::start('generate_elements');
-        $this->generatorPool->process($this->getReaderContext(), $generatorContext);
+
+        $isolatedReaderContext = $this->createIsolatedReaderContext();
+
+        $this->generatorPool->process($isolatedReaderContext, $generatorContext);
         \Magento\Framework\Profiler::stop('generate_elements');
 
         $this->addToOutputRootContainers();
         \Magento\Framework\Profiler::stop(__CLASS__ . '::' . __METHOD__);
     }
 
+    /**
+     * Create isolated reader context to prevent race condition
+     *
+     * @return Context
+     */
+    private function createIsolatedReaderContext(): Context
+    {
+        $originalContext = $this->getReaderContext();
+
+        $originalScheduledStructure = $originalContext->getScheduledStructure();
+        $isolatedScheduledStructure = new Layout\ScheduledStructure(
+            $originalScheduledStructure->__toArray()
+        );
+
+        $originalPageConfig = $originalContext->getPageConfigStructure();
+        $isolatedPageConfig = new \Magento\Framework\View\Page\Config\Structure();
+        $isolatedPageConfig->populateWithArray($originalPageConfig->__toArray());
+
+        // Create new reader context with isolated structures
+        return $this->readerContextFactory->create([
+            'scheduledStructure' => $isolatedScheduledStructure,
+            'pageConfigStructure' => $isolatedPageConfig
+        ]);
+    }
+
     /**
      * Add parent containers to output
      *

lib/internal/Magento/Framework/View/Test/Unit/LayoutTest.php

@@ -897,7 +897,7 @@ public static function isCacheableDataProvider(): array
      */
     public function testGenerateElementsWithoutCache(): void
     {
-        $this->readerContextFactoryMock->expects($this->once())
+        $this->readerContextFactoryMock->expects($this->atMost(2))
             ->method('create')
             ->willReturn($this->readerContextMock);
         $layoutCacheId = 'layout_cache_id';
@@ -952,6 +952,11 @@ public function testGenerateElementsWithoutCache(): void
         $this->layoutScheduledSructure->expects($this->any())
             ->method('__toArray')
             ->willReturn($layoutScheduledStructureData);
+        
+        // Ensure __toArray returns valid data for defensive copying
+        $this->pageConfigStructure->expects($this->any())
+            ->method('__toArray')
+            ->willReturn($pageConfigStructureData);
         $data = [
             'pageConfigStructure' => $pageConfigStructureData,
             'scheduledStructure' => $layoutScheduledStructureData,
@@ -999,7 +1004,7 @@ public function testGenerateElementsWithCache(): void
         $xml = simplexml_load_string('<layout/>', Element::class);
         $this->model->setXml($xml);
 
-        $this->readerContextFactoryMock->expects($this->once())
+        $this->readerContextFactoryMock->expects($this->atMost(2))
             ->method('create')
             ->willReturn($this->readerContextMock);
         $themeMock = $this->getMockForAbstractClass(ThemeInterface::class);
@@ -1035,6 +1040,14 @@ public function testGenerateElementsWithCache(): void
         $this->layoutScheduledSructure->expects($this->once())
             ->method('populateWithArray')
             ->with($layoutScheduledStructureData);
+        
+        // Ensure __toArray returns valid data for defensive copying
+        $this->layoutScheduledSructure->expects($this->any())
+            ->method('__toArray')
+            ->willReturn($layoutScheduledStructureData);
+        $this->pageConfigStructure->expects($this->any())
+            ->method('__toArray')
+            ->willReturn($pageConfigStructureData);
         $data = [
             'pageConfigStructure' => $pageConfigStructureData,
             'scheduledStructure' => $layoutScheduledStructureData,