MC-39718: Process Manager always exits successfully if the amount of …

…functions(i.e. indexer dimensions) is lower than the MAGE_INDEXER_THREADS_COUNT env variable

app/code/Magento/Indexer/Model/ProcessManager.php

@@ -114,6 +114,9 @@ private function multiThreadsExecute($userFunctions)
         // phpcs:ignore Magento2.CodeAnalysis.EmptyBlock,Magento2.Functions.DiscouragedFunction
         while (pcntl_waitpid(0, $status) != -1) {
             //Waiting for the completion of child processes
+            if ($status > 0) {
+                $this->failInChildProcess = true;
+            }
         }
 
         if ($this->failInChildProcess) {

app/code/Magento/Indexer/Test/Unit/Model/ProcessManagerTest.php

@@ -0,0 +1,69 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+declare(strict_types=1);
+
+namespace Magento\Indexer\Test\Unit\Model;
+
+use Magento\Framework\App\ResourceConnection;
+use Magento\Indexer\Model\ProcessManager;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Class covers process manager execution test logic
+ */
+class ProcessManagerTest extends TestCase
+{
+    /**
+     * @dataProvider closureFunctionsProvider
+     * @param array $userFunctions
+     * @param int $threadsCount
+     * @return void
+     */
+    public function testFailureInChildProcessHandleMultiThread(array $userFunctions, int $threadsCount): void
+    {
+        $connectionMock = $this->createMock(ResourceConnection::class);
+        $processManager = new ProcessManager(
+            $connectionMock,
+            null,
+            $threadsCount
+        );
+
+        try {
+            $processManager->execute($userFunctions);
+            $this->fail('Exception was not handled');
+        } catch (\RuntimeException $exception) {
+            $this->assertEquals('Fail in child process', $exception->getMessage());
+        }
+    }
+
+    /**
+     * Closure functions data provider for multi thread execution
+     *
+     * @return array
+     * @SuppressWarnings(PHPMD.ExitExpression)
+     */
+    public function closureFunctionsProvider(): array
+    {
+        return [
+            'more_threads_than_functions' => [
+                'user_functions' => [
+                    // @codingStandardsIgnoreStart
+                    function () {
+                        exit(1);
+                    },
+                    function () {
+                        exit(0);
+                    },
+                    function () {
+                        exit(0);
+                    },
+                    // @codingStandardsIgnoreEnd
+                ],
+                'threads_count' => 4,
+            ],
+        ];
+    }
+}