Cache API: Remove WP_Object_Cache::__destruct() and `wpdb::__destru…

…ct()`.

Originally added in [4686], these constructor/destructor pairings were designed to prevent the objects from being destroyed before shutdown, when output buffers are flushed.

A deeper investigation reveals that this approach didn't quite work as expected and was later made redundant by introducing `wp_ob_end_flush_all()` in [5462].

Props wonderboymusic, nacin, Mte90, SergeyBiryukov.
Fixes #21402.

git-svn-id: https://develop.svn.wordpress.org/trunk@47107 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/cache.php

@@ -335,6 +335,16 @@ class WP_Object_Cache {
 	 */
 	private $multisite;
 
+	/**
+	 * Sets up object properties; PHP 5 style constructor.
+	 *
+	 * @since 2.0.8
+	 */
+	public function __construct() {
+		$this->multisite   = is_multisite();
+		$this->blog_prefix = $this->multisite ? get_current_blog_id() . ':' : '';
+	}
+
 	/**
 	 * Makes private properties readable for backward compatibility.
 	 *
@@ -726,33 +736,4 @@ public function switch_to_blog( $blog_id ) {
 	protected function _exists( $key, $group ) {
 		return isset( $this->cache[ $group ] ) && ( isset( $this->cache[ $group ][ $key ] ) || array_key_exists( $key, $this->cache[ $group ] ) );
 	}
-
-	/**
-	 * Sets up object properties; PHP 5 style constructor.
-	 *
-	 * @since 2.0.8
-	 */
-	public function __construct() {
-		$this->multisite   = is_multisite();
-		$this->blog_prefix = $this->multisite ? get_current_blog_id() . ':' : '';
-
-		/**
-		 * @todo This should be moved to the PHP4 style constructor, PHP5
-		 * already calls __destruct()
-		 */
-		register_shutdown_function( array( $this, '__destruct' ) );
-	}
-
-	/**
-	 * Saves the object cache before object is completely destroyed.
-	 *
-	 * Called upon object destruction, which should be when PHP ends.
-	 *
-	 * @since 2.0.8
-	 *
-	 * @return true Always returns true.
-	 */
-	public function __destruct() {
-		return true;
-	}
 }

src/wp-includes/wp-db.php

@@ -604,8 +604,6 @@ class wpdb {
 	 * @param string $dbhost     MySQL database host
 	 */
 	public function __construct( $dbuser, $dbpassword, $dbname, $dbhost ) {
-		register_shutdown_function( array( $this, '__destruct' ) );
-
 		if ( WP_DEBUG && WP_DEBUG_DISPLAY ) {
 			$this->show_errors();
 		}
@@ -632,17 +630,6 @@ public function __construct( $dbuser, $dbpassword, $dbname, $dbhost ) {
 		$this->db_connect();
 	}
 
-	/**
-	 * PHP5 style destructor and will run when database object is destroyed.
-	 *
-	 * @see wpdb::__construct()
-	 * @since 2.0.8
-	 * @return true
-	 */
-	public function __destruct() {
-		return true;
-	}
-
 	/**
 	 * Makes private properties readable for backward compatibility.
 	 *