ACPT-1413: Child process needs to not close database and other connections in parent

This fixes
* SQL connection getting reused by parent process when the child process is inheriting objects that are already directly referencing the Mysql adapter objects.  This causing transactions to not work properly as the child process is using multiple database connections for what it thinks is the same connection.  It also causes contention problems when multiple children and/or parent try to use connection at the same time.
* SQL connection of parent getting closed when the destructor of child process's connection object getting destroyed.
* Redis connection of parent getting closed when the destructor of child process's connection object getting destroyed.

Author: JacobBrownAustin

lib/internal/Magento/Framework/App/ResourceConnection.php

@@ -174,7 +174,12 @@ public function getConnectionByName($connectionName)
      */
     private function getProcessConnectionName($connectionName)
     {
-        return $connectionName . '_process_' . getmypid();
+        // Note: We cannot have separate connections in this class based ond the process id.
+        // The reason is because some objects have references to the connection object before the fork,
+        // and therefore the child would be accessing a different data connection in some classes,  which could break
+        // the expected transaction functionality.
+        // We added avoidReusingParentProcessConnection() in Mysql adapter to avoid using the parent's connection.
+        return $connectionName;
     }
 
     /**

lib/internal/Magento/Framework/Cache/Frontend/Adapter/Zend.php

@@ -29,6 +29,13 @@ class Zend implements \Magento\Framework\Cache\FrontendInterface
      */
     private $pid;
 
+    /**
+     * We need to keep references to parent's frontends so that they don't get destroyed
+     *
+     * @var array
+     */
+    private $parentFrontends = [];
+
     /**
      * @param \Closure $frontendFactory
      */
@@ -147,6 +154,9 @@ private function getFrontEnd()
         if (getmypid() === $this->pid) {
             return $this->_frontend;
         }
+        // Note: We hide the parent process's _frontend so that the destructor won't get called on it.
+        // If the destructor were called, then the parent process's connection would be disconnected.
+        $this->parentFrontends[] = $this->_frontend;
         $frontendFactory = $this->frontendFactory;
         $this->_frontend = $frontendFactory();
         $this->pid = getmypid();

lib/internal/Magento/Framework/Config/Data/Scoped.php

@@ -22,27 +22,6 @@ class Scoped extends \Magento\Framework\Config\Data
      */
     protected $_configScope;
 
-    /**
-     * Configuration reader
-     *
-     * @var \Magento\Framework\Config\ReaderInterface
-     */
-    protected $_reader;
-
-    /**
-     * Configuration cache
-     *
-     * @var \Magento\Framework\Config\CacheInterface
-     */
-    protected $_cache;
-
-    /**
-     * Cache tag
-     *
-     * @var string
-     */
-    protected $_cacheId;
-
     /**
      * Scope priority loading scheme
      *

lib/internal/Magento/Framework/DB/Adapter/Pdo/Mysql.php

@@ -237,6 +237,20 @@ class Mysql extends \Zend_Db_Adapter_Pdo_Mysql implements AdapterInterface, Rese
      */
     private $schemaListener;
 
+    /**
+     * Process id that the connection is associated with
+     *
+     * @var int|null
+     */
+    private ?int $pid = null;
+
+    /**
+     * Parent process's database connection
+     *
+     * @var array
+     */
+    private $parentConnections = [];
+
     /**
      * Constructor
      *
@@ -255,6 +269,7 @@ public function __construct(
         array $config = [],
         SerializerInterface $serializer = null
     ) {
+        $this->pid = getmypid();
         $this->string = $string;
         $this->dateTime = $dateTime;
         $this->logger = $logger;
@@ -295,6 +310,7 @@ public function _resetState() : void
         $this->_isDdlCacheAllowed = true;
         $this->isMysql8Engine = null;
         $this->_queryHook = null;
+        $this->avoidReusingParentProcessConnection();
         $this->closeConnection();
     }
 
@@ -397,6 +413,23 @@ public function convertDateTime($datetime)
         return $this->formatDate($datetime, true);
     }
 
+    /**
+     * If the connection is associated to a different process id, then we need to not use it.
+     *
+     * @return void
+     */
+    private function avoidReusingParentProcessConnection()
+    {
+        if (getmypid() != $this->pid) {
+            // Note: we hide parent's connection into parentConnections so that the destructor isn't called on it.
+            // Because if destructor is called, it causes parent's connection to die
+            // We store in array, if parent is also hiding its parent's connection
+            $this->parentConnections[] = $this->_connection;
+            $this->_connection = null;
+            $this->pid = getmypid();
+        }
+    }
+
     /**
      * Creates a PDO object and connects to the database.
      *
@@ -409,6 +442,7 @@ public function convertDateTime($datetime)
      */
     protected function _connect()
     {
+        $this->avoidReusingParentProcessConnection();
         if ($this->_connection) {
             return;
         }