Cache API: Add wp_cache_flush_group function.

Add a new plugable function called `wp_cache_flush_group`, that will allow developers to clear whole cache groups with a single call. Developers can detect if their current implementation of an object cache supports flushing by group, by calling `wp_cache_supports_group_flush` which returns true if it is supported. If the developers of the object cache drop-in has not implemented `wp_cache_flush_group` and `wp_cache_supports_group_flush`, these functions are polyfilled and `wp_cache_supports_group_flush` defaults to false.

Props Spacedmonkey, filosofo, ryan, sc0ttkclark, SergeyBiryukov, scribu, Ste_95, dd32, dhilditch, dougal, lucasbustamante, dg12345, tillkruess, peterwilsoncc, flixos90, pbearne.
Fixes WordPress#4476.

git-svn-id: https://develop.svn.wordpress.org/trunk@53763 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/cache-compat.php

@@ -141,3 +141,49 @@ function wp_cache_flush_runtime() {
 		return wp_using_ext_object_cache() ? false : wp_cache_flush();
 	}
 endif;
+
+if ( ! function_exists( 'wp_cache_flush_group' ) ) :
+	/**
+	 * Removes all cache items in a group, if the object cache implementation supports it.
+	 * Before calling this method, always check for group flushing support using the
+	 * `wp_cache_supports_group_flush()` method.
+	 *
+	 * @since 6.1.0
+	 *
+	 * @see WP_Object_Cache::flush_group()
+	 * @global WP_Object_Cache $wp_object_cache Object cache global instance.
+	 *
+	 * @param string $group Name of group to remove from cache.
+	 * @return bool True if group was flushed, false otherwise.
+	 */
+	function wp_cache_flush_group( $group ) {
+		global $wp_object_cache;
+
+		if ( ! wp_cache_supports_group_flush() ) {
+			_doing_it_wrong(
+				__FUNCTION__,
+				__( 'Your object cache implementation does not support flushing individual groups.' ),
+				'6.1.0'
+			);
+
+			return false;
+		}
+
+		return $wp_object_cache->flush_group( $group );
+	}
+endif;
+
+if ( ! function_exists( 'wp_cache_supports_group_flush' ) ) :
+	/**
+	 * Whether the object cache implementation supports flushing individual cache groups.
+	 *
+	 * @since 6.1.0
+	 *
+	 * @see WP_Object_Cache::flush_group()
+	 *
+	 * @return bool True if group flushing is supported, false otherwise.
+	 */
+	function wp_cache_supports_group_flush() {
+		return false;
+	}
+endif;

src/wp-includes/cache.php

@@ -22,6 +22,19 @@ function wp_cache_init() {
 	$GLOBALS['wp_object_cache'] = new WP_Object_Cache();
 }
 
+/**
+ * Whether the object cache implementation supports flushing individual cache groups.
+ *
+ * @since 6.1.0
+ *
+ * @see WP_Object_Cache::flush_group()
+ *
+ * @return bool True if group flushing is supported, false otherwise.
+ */
+function wp_cache_supports_group_flush() {
+	return true;
+}
+
 /**
  * Adds data to the cache, if the cache key doesn't already exist.
  *
@@ -281,6 +294,25 @@ function wp_cache_flush_runtime() {
 	return wp_cache_flush();
 }
 
+/**
+ * Removes all cache items in a group, if the object cache implementation supports it.
+ * Before calling this method, always check for group flushing support using the
+ * `wp_cache_supports_group_flush()` method.
+ *
+ * @since 6.1.0
+ *
+ * @see WP_Object_Cache::flush_group()
+ * @global WP_Object_Cache $wp_object_cache Object cache global instance.
+ *
+ * @param string $group Name of group to remove from cache.
+ * @return bool True if group was flushed, false otherwise.
+ */
+function wp_cache_flush_group( $group ) {
+	global $wp_object_cache;
+
+	return $wp_object_cache->flush_group( $group );
+}
+
 /**
  * Closes the cache.
  *

src/wp-includes/class-wp-object-cache.php

@@ -290,6 +290,20 @@ public function set_multiple( array $data, $group = '', $expire = 0 ) {
 		return $values;
 	}
 
+	/**
+	 * Removes all cache items in a group.
+	 *
+	 * @since 6.1.0
+	 *
+	 * @param string $group Name of group to remove from cache.
+	 * @return true Always returns true.
+	 */
+	public function flush_group( $group ) {
+		unset( $this->cache[ $group ] );
+
+		return true;
+	}
+
 	/**
 	 * Retrieves the cache contents, if it exists.
 	 *

tests/phpunit/includes/object-cache.php

@@ -745,6 +745,17 @@ function wp_cache_init() {
 	$wp_object_cache = new WP_Object_Cache();
 }
 
+/**
+ * Whether the object cache implementation supports flushing individual cache groups.
+ *
+ * @since 6.1.0
+ *
+ * @return bool True if group flushing is supported, false otherwise.
+ */
+function wp_cache_supports_group_flush() {
+	return false;
+}
+
 /**
  * Adds a group or set of groups to the list of non-persistent groups.
  *

tests/phpunit/tests/cache.php

@@ -415,4 +415,36 @@ public function test_wp_cache_delete_multiple() {
 
 		$this->assertSame( $expected, $found );
 	}
+
+	/**
+	 * @ticket 4476
+	 * @ticket 9773
+	 *
+	 * test wp_cache_flush_group
+	 *
+	 * @covers ::wp_cache_flush_group
+	 */
+	public function test_wp_cache_flush_group() {
+		$key = 'my-key';
+		$val = 'my-val';
+
+		wp_cache_set( $key, $val, 'group-test' );
+		wp_cache_set( $key, $val, 'group-kept' );
+
+		$this->assertSame( $val, wp_cache_get( $key, 'group-test' ), 'test_wp_cache_flush_group: group-test should contain my-val' );
+
+		if ( wp_using_ext_object_cache() ) {
+			$this->setExpectedIncorrectUsage( 'wp_cache_flush_group' );
+		}
+
+		$results = wp_cache_flush_group( 'group-test' );
+
+		if ( wp_using_ext_object_cache() ) {
+			$this->assertFalse( $results );
+		} else {
+			$this->assertTrue( $results );
+			$this->assertFalse( wp_cache_get( $key, 'group-test' ), 'test_wp_cache_flush_group: group-test should return false' );
+			$this->assertSame( $val, wp_cache_get( $key, 'group-kept' ), 'test_wp_cache_flush_group: group-kept should still contain my-val' );
+		}
+	}
 }

tests/phpunit/tests/pluggable.php

@@ -268,6 +268,7 @@ public function get_pluggable_function_signatures() {
 
 					// wp-includes/cache.php:
 					'wp_cache_init'                      => array(),
+					'wp_cache_supports_group_flush'      => array(),
 					'wp_cache_add'                       => array(
 						'key',
 						'data',
@@ -327,6 +328,7 @@ public function get_pluggable_function_signatures() {
 					),
 					'wp_cache_flush'                     => array(),
 					'wp_cache_flush_runtime'             => array(),
+					'wp_cache_flush_group'               => array( 'group' ),
 					'wp_cache_close'                     => array(),
 					'wp_cache_add_global_groups'         => array( 'groups' ),
 					'wp_cache_add_non_persistent_groups' => array( 'groups' ),