diff --git a/application/config/mimes.php b/application/config/mimes.php
index 0ec9db0..7aa5c9e 100644
--- a/application/config/mimes.php
+++ b/application/config/mimes.php
@@ -140,7 +140,7 @@
 	'f4v'   =>	array('video/mp4', 'video/x-f4v'),
 	'flv'	=>	'video/x-flv',
 	'webm'	=>	'video/webm',
-	'aac'   =>	'audio/x-acc',
+	'aac'   =>	array('audio/x-aac', 'audio/aac'),
 	'm4u'   =>	'application/vnd.mpegurl',
 	'm3u'   =>	'text/plain',
 	'xspf'  =>	'application/xspf+xml',
diff --git a/system/core/CodeIgniter.php b/system/core/CodeIgniter.php
index 56826f1..8aecc0a 100644
--- a/system/core/CodeIgniter.php
+++ b/system/core/CodeIgniter.php
@@ -55,7 +55,7 @@
  * @var	string
  *
  */
-	const CI_VERSION = '3.1.10';
+	const CI_VERSION = '3.1.11';
 
 /*
  * ------------------------------------------------------
diff --git a/system/core/Controller.php b/system/core/Controller.php
index 2bb1578..e25b847 100644
--- a/system/core/Controller.php
+++ b/system/core/Controller.php
@@ -58,6 +58,13 @@ class CI_Controller {
 	 */
 	private static $instance;
 
+	/**
+	 * CI_Loader
+	 *
+	 * @var	CI_Loader
+	 */
+	public $load;
+
 	/**
 	 * Class constructor
 	 *
diff --git a/system/core/Log.php b/system/core/Log.php
index 4338aa9..f37726e 100644
--- a/system/core/Log.php
+++ b/system/core/Log.php
@@ -247,11 +247,11 @@ public function write_log($level, $msg)
 	 * @param	string	$level 	The error level
 	 * @param	string	$date 	Formatted date string
 	 * @param	string	$message 	The log message
-	 * @return	string	Formatted log line with a new line character '\n' at the end
+	 * @return	string	Formatted log line with a new line character at the end
 	 */
 	protected function _format_line($level, $date, $message)
 	{
-		return $level.' - '.$date.' --> '.$message."\n";
+		return $level.' - '.$date.' --> '.$message.PHP_EOL;
 	}
 
 	// --------------------------------------------------------------------
diff --git a/system/core/Security.php b/system/core/Security.php
index 883968e..6a81faf 100644
--- a/system/core/Security.php
+++ b/system/core/Security.php
@@ -228,6 +228,7 @@ public function csrf_verify()
 
 		// Check CSRF token validity, but don't error on mismatch just yet - we'll want to regenerate
 		$valid = isset($_POST[$this->_csrf_token_name], $_COOKIE[$this->_csrf_cookie_name])
+			&& is_string($_POST[$this->_csrf_token_name]) && is_string($_COOKIE[$this->_csrf_cookie_name])
 			&& hash_equals($_POST[$this->_csrf_token_name], $_COOKIE[$this->_csrf_cookie_name]);
 
 		// We kill this since we're done and we don't want to pollute the _POST array
diff --git a/system/database/DB_result.php b/system/database/DB_result.php
index 0dbac16..ed5252d 100644
--- a/system/database/DB_result.php
+++ b/system/database/DB_result.php
@@ -381,7 +381,7 @@ public function set_row($key, $value = NULL)
 	 */
 	public function custom_row_object($n, $type)
 	{
-		isset($this->custom_result_object[$type]) OR $this->custom_result_object($type);
+		isset($this->custom_result_object[$type]) OR $this->custom_result_object[$type] = $this->custom_result_object($type);
 
 		if (count($this->custom_result_object[$type]) === 0)
 		{
diff --git a/system/database/drivers/mysql/mysql_driver.php b/system/database/drivers/mysql/mysql_driver.php
index 78e77bc..440715a 100644
--- a/system/database/drivers/mysql/mysql_driver.php
+++ b/system/database/drivers/mysql/mysql_driver.php
@@ -383,7 +383,7 @@ public function insert_id()
 	 */
 	protected function _list_tables($prefix_limit = FALSE)
 	{
-		$sql = 'SHOW TABLES FROM '.$this->escape_identifiers($this->database);
+		$sql = 'SHOW TABLES FROM '.$this->_escape_char.$this->database.$this->_escape_char;
 
 		if ($prefix_limit !== FALSE && $this->dbprefix !== '')
 		{
diff --git a/system/database/drivers/mysqli/mysqli_driver.php b/system/database/drivers/mysqli/mysqli_driver.php
index d374e01..0ca0f48 100644
--- a/system/database/drivers/mysqli/mysqli_driver.php
+++ b/system/database/drivers/mysqli/mysqli_driver.php
@@ -429,7 +429,7 @@ public function insert_id()
 	 */
 	protected function _list_tables($prefix_limit = FALSE)
 	{
-		$sql = 'SHOW TABLES FROM '.$this->escape_identifiers($this->database);
+		$sql = 'SHOW TABLES FROM '.$this->_escape_char.$this->database.$this->_escape_char;
 
 		if ($prefix_limit !== FALSE && $this->dbprefix !== '')
 		{
diff --git a/system/database/drivers/oci8/oci8_forge.php b/system/database/drivers/oci8/oci8_forge.php
index 20217f2..58f3c39 100644
--- a/system/database/drivers/oci8/oci8_forge.php
+++ b/system/database/drivers/oci8/oci8_forge.php
@@ -81,6 +81,13 @@ class CI_DB_oci8_forge extends CI_DB_forge {
 	 */
 	protected $_unsigned		= FALSE;
 
+	/**
+	 * NULL value representation in CREATE/ALTER TABLE statements
+	 *
+	 * @var	string
+	 */
+	protected $_null		= 'NULL';
+
 	// --------------------------------------------------------------------
 
 	/**
diff --git a/system/database/drivers/pdo/pdo_result.php b/system/database/drivers/pdo/pdo_result.php
index 03c0f9f..b3973da 100644
--- a/system/database/drivers/pdo/pdo_result.php
+++ b/system/database/drivers/pdo/pdo_result.php
@@ -133,7 +133,7 @@ public function field_data()
 
 				$retval[$i]			= new stdClass();
 				$retval[$i]->name		= $field['name'];
-				$retval[$i]->type		= $field['native_type'];
+				$retval[$i]->type		= isset($field['native_type']) ? $field['native_type'] : null;
 				$retval[$i]->max_length		= ($field['len'] > 0) ? $field['len'] : NULL;
 				$retval[$i]->primary_key	= (int) ( ! empty($field['flags']) && in_array('primary_key', $field['flags'], TRUE));
 			}
diff --git a/system/database/drivers/pdo/subdrivers/pdo_firebird_forge.php b/system/database/drivers/pdo/subdrivers/pdo_firebird_forge.php
index 54752f1..eceb597 100644
--- a/system/database/drivers/pdo/subdrivers/pdo_firebird_forge.php
+++ b/system/database/drivers/pdo/subdrivers/pdo_firebird_forge.php
@@ -150,7 +150,7 @@ protected function _alter_table($alter_type, $table, $field)
 			if ( ! empty($field[$i]['default']))
 			{
 				$sqls[] = $sql.' ALTER COLUMN '.$this->db->escape_identifiers($field[$i]['name'])
-					.' SET DEFAULT '.$field[$i]['default'];
+					.' SET '.$field[$i]['default'];
 			}
 
 			if (isset($field[$i]['null']))
diff --git a/system/database/drivers/pdo/subdrivers/pdo_mysql_driver.php b/system/database/drivers/pdo/subdrivers/pdo_mysql_driver.php
index 26bc30e..73b88bc 100644
--- a/system/database/drivers/pdo/subdrivers/pdo_mysql_driver.php
+++ b/system/database/drivers/pdo/subdrivers/pdo_mysql_driver.php
@@ -279,7 +279,7 @@ protected function _trans_rollback()
 	 */
 	protected function _list_tables($prefix_limit = FALSE)
 	{
-		$sql = 'SHOW TABLES';
+		$sql = 'SHOW TABLES FROM '.$this->_escape_char.$this->database.$this->_escape_char;
 
 		if ($prefix_limit === TRUE && $this->dbprefix !== '')
 		{
diff --git a/system/database/drivers/pdo/subdrivers/pdo_oci_forge.php b/system/database/drivers/pdo/subdrivers/pdo_oci_forge.php
index 0abda59..b5d3eb1 100644
--- a/system/database/drivers/pdo/subdrivers/pdo_oci_forge.php
+++ b/system/database/drivers/pdo/subdrivers/pdo_oci_forge.php
@@ -74,6 +74,13 @@ class CI_DB_pdo_oci_forge extends CI_DB_pdo_forge {
 	 */
 	protected $_unsigned		= FALSE;
 
+	/**
+	 * NULL value representation in CREATE/ALTER TABLE statements
+	 *
+	 * @var	string
+	 */
+	protected $_null		= 'NULL';
+
 	// --------------------------------------------------------------------
 
 	/**
diff --git a/system/database/drivers/pdo/subdrivers/pdo_pgsql_driver.php b/system/database/drivers/pdo/subdrivers/pdo_pgsql_driver.php
index b05d473..2d0c74b 100644
--- a/system/database/drivers/pdo/subdrivers/pdo_pgsql_driver.php
+++ b/system/database/drivers/pdo/subdrivers/pdo_pgsql_driver.php
@@ -98,7 +98,7 @@ public function __construct($params)
 
 			if ( ! empty($this->username))
 			{
-				$this->dsn .= ';username='.$this->username;
+				$this->dsn .= ';user='.$this->username;
 				empty($this->password) OR $this->dsn .= ';password='.$this->password;
 			}
 		}
diff --git a/system/database/drivers/pdo/subdrivers/pdo_pgsql_forge.php b/system/database/drivers/pdo/subdrivers/pdo_pgsql_forge.php
index ff7a110..a4ccff4 100644
--- a/system/database/drivers/pdo/subdrivers/pdo_pgsql_forge.php
+++ b/system/database/drivers/pdo/subdrivers/pdo_pgsql_forge.php
@@ -130,7 +130,7 @@ protected function _alter_table($alter_type, $table, $field)
 			if ( ! empty($field[$i]['default']))
 			{
 				$sqls[] = $sql.' ALTER COLUMN '.$this->db->escape_identifiers($field[$i]['name'])
-					.' SET DEFAULT '.$field[$i]['default'];
+					.' SET '.$field[$i]['default'];
 			}
 
 			if (isset($field[$i]['null']))
diff --git a/system/database/drivers/postgre/postgre_forge.php b/system/database/drivers/postgre/postgre_forge.php
index 353ddac..481e222 100644
--- a/system/database/drivers/postgre/postgre_forge.php
+++ b/system/database/drivers/postgre/postgre_forge.php
@@ -125,7 +125,7 @@ protected function _alter_table($alter_type, $table, $field)
 			if ( ! empty($field[$i]['default']))
 			{
 				$sqls[] = $sql.' ALTER COLUMN '.$this->db->escape_identifiers($field[$i]['name'])
-					.' SET DEFAULT '.$field[$i]['default'];
+					.' SET '.$field[$i]['default'];
 			}
 
 			if (isset($field[$i]['null']))
diff --git a/system/libraries/Cache/drivers/Cache_redis.php b/system/libraries/Cache/drivers/Cache_redis.php
index 3759618..bff96fb 100644
--- a/system/libraries/Cache/drivers/Cache_redis.php
+++ b/system/libraries/Cache/drivers/Cache_redis.php
@@ -76,6 +76,13 @@ class CI_Cache_redis extends CI_Driver
 	 */
 	protected $_serialized = array();
 
+	/**
+	 * del()/delete() method name depending on phpRedis version
+	 *
+	 * @var	string
+	 */
+	protected static $_delete_name;
+
 	// ------------------------------------------------------------------------
 
 	/**
@@ -97,6 +104,10 @@ public function __construct()
 			return;
 		}
 
+		isset(static::$_delete_name) OR static::$_delete_name = version_compare(phpversion('phpredis'), '5', '>=')
+			? 'del'
+			: 'delete';
+
 		$CI =& get_instance();
 
 		if ($CI->config->load('redis', TRUE, TRUE))
@@ -135,10 +146,6 @@ public function __construct()
 		{
 			log_message('error', 'Cache: Redis connection refused ('.$e->getMessage().')');
 		}
-
-		// Initialize the index of serialized values.
-		$serialized = $this->_redis->sMembers('_ci_redis_serialized');
-		empty($serialized) OR $this->_serialized = array_flip($serialized);
 	}
 
 	// ------------------------------------------------------------------------
@@ -153,7 +160,7 @@ public function get($key)
 	{
 		$value = $this->_redis->get($key);
 
-		if ($value !== FALSE && isset($this->_serialized[$key]))
+		if ($value !== FALSE && $this->_redis->sIsMember('_ci_redis_serialized', $key))
 		{
 			return unserialize($value);
 		}
@@ -184,9 +191,8 @@ public function save($id, $data, $ttl = 60, $raw = FALSE)
 			isset($this->_serialized[$id]) OR $this->_serialized[$id] = TRUE;
 			$data = serialize($data);
 		}
-		elseif (isset($this->_serialized[$id]))
+		else
 		{
-			$this->_serialized[$id] = NULL;
 			$this->_redis->sRemove('_ci_redis_serialized', $id);
 		}
 
@@ -203,16 +209,12 @@ public function save($id, $data, $ttl = 60, $raw = FALSE)
 	 */
 	public function delete($key)
 	{
-		if ($this->_redis->delete($key) !== 1)
+		if ($this->_redis->{static::$_delete_name}($key) !== 1)
 		{
 			return FALSE;
 		}
 
-		if (isset($this->_serialized[$key]))
-		{
-			$this->_serialized[$key] = NULL;
-			$this->_redis->sRemove('_ci_redis_serialized', $key);
-		}
+		$this->_redis->sRemove('_ci_redis_serialized', $key);
 
 		return TRUE;
 	}
@@ -228,7 +230,7 @@ public function delete($key)
 	 */
 	public function increment($id, $offset = 1)
 	{
-		return $this->_redis->incr($id, $offset);
+		return $this->_redis->incrBy($id, $offset);
 	}
 
 	// ------------------------------------------------------------------------
@@ -242,7 +244,7 @@ public function increment($id, $offset = 1)
 	 */
 	public function decrement($id, $offset = 1)
 	{
-		return $this->_redis->decr($id, $offset);
+		return $this->_redis->decrBy($id, $offset);
 	}
 
 	// ------------------------------------------------------------------------
diff --git a/system/libraries/Form_validation.php b/system/libraries/Form_validation.php
index 1bd5549..fdf2020 100644
--- a/system/libraries/Form_validation.php
+++ b/system/libraries/Form_validation.php
@@ -1208,6 +1208,13 @@ public function valid_url($str)
 			$str = $matches[2];
 		}
 
+		// Apparently, FILTER_VALIDATE_URL doesn't reject digit-only names for some reason ...
+		// See https://github.com/bcit-ci/CodeIgniter/issues/5755
+		if (ctype_digit($str))
+		{
+			return FALSE;
+		}
+
 		// PHP 7 accepts IPv6 addresses within square brackets as hostnames,
 		// but it appears that the PR that came in with https://bugs.php.net/bug.php?id=68039
 		// was never merged into a PHP 5 branch ... https://3v4l.org/8PsSN
diff --git a/system/libraries/Session/Session_driver.php b/system/libraries/Session/Session_driver.php
index 14ebdb0..dbc8337 100644
--- a/system/libraries/Session/Session_driver.php
+++ b/system/libraries/Session/Session_driver.php
@@ -184,25 +184,4 @@ protected function _release_lock()
 
 		return TRUE;
 	}
-
-	// ------------------------------------------------------------------------
-
-	/**
-	 * Fail
-	 *
-	 * Drivers other than the 'files' one don't (need to) use the
-	 * session.save_path INI setting, but that leads to confusing
-	 * error messages emitted by PHP when open() or write() fail,
-	 * as the message contains session.save_path ...
-	 * To work around the problem, the drivers will call this method
-	 * so that the INI is set just in time for the error message to
-	 * be properly generated.
-	 *
-	 * @return	mixed
-	 */
-	protected function _fail()
-	{
-		ini_set('session.save_path', config_item('sess_save_path'));
-		return $this->_failure;
-	}
 }
diff --git a/system/libraries/Session/drivers/Session_database_driver.php b/system/libraries/Session/drivers/Session_database_driver.php
index 734fe62..89afe34 100644
--- a/system/libraries/Session/drivers/Session_database_driver.php
+++ b/system/libraries/Session/drivers/Session_database_driver.php
@@ -130,7 +130,7 @@ public function open($save_path, $name)
 	{
 		if (empty($this->_db->conn_id) && ! $this->_db->db_connect())
 		{
-			return $this->_fail();
+			return $this->_failure;
 		}
 
 		$this->php5_validate_id();
@@ -150,48 +150,47 @@ public function open($save_path, $name)
 	 */
 	public function read($session_id)
 	{
-		if ($this->_get_lock($session_id) !== FALSE)
+		if ($this->_get_lock($session_id) === FALSE)
 		{
-			// Prevent previous QB calls from messing with our queries
-			$this->_db->reset_query();
-
-			// Needed by write() to detect session_regenerate_id() calls
-			$this->_session_id = $session_id;
+			return $this->_failure;
+		}
 
-			$this->_db
-				->select('data')
-				->from($this->_config['save_path'])
-				->where('id', $session_id);
+		// Prevent previous QB calls from messing with our queries
+		$this->_db->reset_query();
 
-			if ($this->_config['match_ip'])
-			{
-				$this->_db->where('ip_address', $_SERVER['REMOTE_ADDR']);
-			}
+		// Needed by write() to detect session_regenerate_id() calls
+		$this->_session_id = $session_id;
 
-			if ( ! ($result = $this->_db->get()) OR ($result = $result->row()) === NULL)
-			{
-				// PHP7 will reuse the same SessionHandler object after
-				// ID regeneration, so we need to explicitly set this to
-				// FALSE instead of relying on the default ...
-				$this->_row_exists = FALSE;
-				$this->_fingerprint = md5('');
-				return '';
-			}
+		$this->_db
+			->select('data')
+			->from($this->_config['save_path'])
+			->where('id', $session_id);
 
-			// PostgreSQL's variant of a BLOB datatype is Bytea, which is a
-			// PITA to work with, so we use base64-encoded data in a TEXT
-			// field instead.
-			$result = ($this->_platform === 'postgre')
-				? base64_decode(rtrim($result->data))
-				: $result->data;
+		if ($this->_config['match_ip'])
+		{
+			$this->_db->where('ip_address', $_SERVER['REMOTE_ADDR']);
+		}
 
-			$this->_fingerprint = md5($result);
-			$this->_row_exists = TRUE;
-			return $result;
+		if ( ! ($result = $this->_db->get()) OR ($result = $result->row()) === NULL)
+		{
+			// PHP7 will reuse the same SessionHandler object after
+			// ID regeneration, so we need to explicitly set this to
+			// FALSE instead of relying on the default ...
+			$this->_row_exists = FALSE;
+			$this->_fingerprint = md5('');
+			return '';
 		}
 
-		$this->_fingerprint = md5('');
-		return '';
+		// PostgreSQL's variant of a BLOB datatype is Bytea, which is a
+		// PITA to work with, so we use base64-encoded data in a TEXT
+		// field instead.
+		$result = ($this->_platform === 'postgre')
+			? base64_decode(rtrim($result->data))
+			: $result->data;
+
+		$this->_fingerprint = md5($result);
+		$this->_row_exists = TRUE;
+		return $result;
 	}
 
 	// ------------------------------------------------------------------------
@@ -215,7 +214,7 @@ public function write($session_id, $session_data)
 		{
 			if ( ! $this->_release_lock() OR ! $this->_get_lock($session_id))
 			{
-				return $this->_fail();
+				return $this->_failure;
 			}
 
 			$this->_row_exists = FALSE;
@@ -223,7 +222,7 @@ public function write($session_id, $session_data)
 		}
 		elseif ($this->_lock === FALSE)
 		{
-			return $this->_fail();
+			return $this->_failure;
 		}
 
 		if ($this->_row_exists === FALSE)
@@ -242,7 +241,7 @@ public function write($session_id, $session_data)
 				return $this->_success;
 			}
 
-			return $this->_fail();
+			return $this->_failure;
 		}
 
 		$this->_db->where('id', $session_id);
@@ -265,7 +264,7 @@ public function write($session_id, $session_data)
 			return $this->_success;
 		}
 
-		return $this->_fail();
+		return $this->_failure;
 	}
 
 	// ------------------------------------------------------------------------
@@ -280,7 +279,7 @@ public function write($session_id, $session_data)
 	public function close()
 	{
 		return ($this->_lock && ! $this->_release_lock())
-			? $this->_fail()
+			? $this->_failure
 			: $this->_success;
 	}
 
@@ -309,7 +308,7 @@ public function destroy($session_id)
 
 			if ( ! $this->_db->delete($this->_config['save_path']))
 			{
-				return $this->_fail();
+				return $this->_failure;
 			}
 		}
 
@@ -319,7 +318,7 @@ public function destroy($session_id)
 			return $this->_success;
 		}
 
-		return $this->_fail();
+		return $this->_failure;
 	}
 
 	// ------------------------------------------------------------------------
@@ -339,7 +338,7 @@ public function gc($maxlifetime)
 
 		return ($this->_db->delete($this->_config['save_path'], 'timestamp < '.(time() - $maxlifetime)))
 			? $this->_success
-			: $this->_fail();
+			: $this->_failure;
 	}
 
 	// --------------------------------------------------------------------
diff --git a/system/libraries/Session/drivers/Session_files_driver.php b/system/libraries/Session/drivers/Session_files_driver.php
index 4670594..2899b7d 100644
--- a/system/libraries/Session/drivers/Session_files_driver.php
+++ b/system/libraries/Session/drivers/Session_files_driver.php
@@ -135,12 +135,14 @@ public function open($save_path, $name)
 		{
 			if ( ! mkdir($save_path, 0700, TRUE))
 			{
-				throw new Exception("Session: Configured save path '".$this->_config['save_path']."' is not a directory, doesn't exist or cannot be created.");
+				log_message('error', "Session: Configured save path '".$this->_config['save_path']."' is not a directory, doesn't exist or cannot be created.");
+				return $this->_failure;
 			}
 		}
 		elseif ( ! is_writable($save_path))
 		{
-			throw new Exception("Session: Configured save path '".$this->_config['save_path']."' is not writable by the PHP process.");
+			log_message('error', "Session: Configured save path '".$this->_config['save_path']."' is not writable by the PHP process.");
+			return $this->_failure;
 		}
 
 		$this->_config['save_path'] = $save_path;
diff --git a/system/libraries/Session/drivers/Session_memcached_driver.php b/system/libraries/Session/drivers/Session_memcached_driver.php
index ab54f02..854adf8 100644
--- a/system/libraries/Session/drivers/Session_memcached_driver.php
+++ b/system/libraries/Session/drivers/Session_memcached_driver.php
@@ -117,7 +117,7 @@ public function open($save_path, $name)
 		{
 			$this->_memcached = NULL;
 			log_message('error', 'Session: Invalid Memcached save path format: '.$this->_config['save_path']);
-			return $this->_fail();
+			return $this->_failure;
 		}
 
 		foreach ($matches as $match)
@@ -142,7 +142,7 @@ public function open($save_path, $name)
 		if (empty($server_list))
 		{
 			log_message('error', 'Session: Memcached server pool is empty.');
-			return $this->_fail();
+			return $this->_failure;
 		}
 
 		$this->php5_validate_id();
@@ -172,7 +172,7 @@ public function read($session_id)
 			return $session_data;
 		}
 
-		return $this->_fail();
+		return $this->_failure;
 	}
 
 	// ------------------------------------------------------------------------
@@ -190,14 +190,14 @@ public function write($session_id, $session_data)
 	{
 		if ( ! isset($this->_memcached, $this->_lock_key))
 		{
-			return $this->_fail();
+			return $this->_failure;
 		}
 		// Was the ID regenerated?
 		elseif ($session_id !== $this->_session_id)
 		{
 			if ( ! $this->_release_lock() OR ! $this->_get_lock($session_id))
 			{
-				return $this->_fail();
+				return $this->_failure;
 			}
 
 			$this->_fingerprint = md5('');
@@ -215,7 +215,7 @@ public function write($session_id, $session_data)
 				return $this->_success;
 			}
 
-			return $this->_fail();
+			return $this->_failure;
 		}
 		elseif (
 			$this->_memcached->touch($key, $this->_config['expiration'])
@@ -225,7 +225,7 @@ public function write($session_id, $session_data)
 			return $this->_success;
 		}
 
-		return $this->_fail();
+		return $this->_failure;
 	}
 
 	// ------------------------------------------------------------------------
@@ -244,14 +244,14 @@ public function close()
 			$this->_release_lock();
 			if ( ! $this->_memcached->quit())
 			{
-				return $this->_fail();
+				return $this->_failure;
 			}
 
 			$this->_memcached = NULL;
 			return $this->_success;
 		}
 
-		return $this->_fail();
+		return $this->_failure;
 	}
 
 	// ------------------------------------------------------------------------
@@ -273,7 +273,7 @@ public function destroy($session_id)
 			return $this->_success;
 		}
 
-		return $this->_fail();
+		return $this->_failure;
 	}
 
 	// ------------------------------------------------------------------------
diff --git a/system/libraries/Session/drivers/Session_redis_driver.php b/system/libraries/Session/drivers/Session_redis_driver.php
index 434b11e..df38174 100644
--- a/system/libraries/Session/drivers/Session_redis_driver.php
+++ b/system/libraries/Session/drivers/Session_redis_driver.php
@@ -76,6 +76,33 @@ class CI_Session_redis_driver extends CI_Session_driver implements SessionHandle
 	 */
 	protected $_key_exists = FALSE;
 
+	/**
+	 * Name of setTimeout() method in phpRedis
+	 *
+	 * Due to some deprecated methods in phpRedis, we need to call the
+	 * specific methods depending on the version of phpRedis.
+	 *
+	 * @var string
+	 */
+	protected $_setTimeout_name;
+
+	/**
+	 * Name of delete() method in phpRedis
+	 *
+	 * Due to some deprecated methods in phpRedis, we need to call the
+	 * specific methods depending on the version of phpRedis.
+	 *
+	 * @var string
+	 */
+	protected $_delete_name;
+
+	/**
+	 * Success return value of ping() method in phpRedis
+	 *
+	 * @var mixed
+	 */
+	protected $_ping_success;
+
 	// ------------------------------------------------------------------------
 
 	/**
@@ -88,6 +115,20 @@ public function __construct(&$params)
 	{
 		parent::__construct($params);
 
+		// Detect the names of some methods in phpRedis instance
+		if (version_compare(phpversion('redis'), '5', '>='))
+		{
+			$this->_setTimeout_name = 'expire';
+			$this->_delete_name = 'del';
+			$this->_ping_success = TRUE;
+		}
+		else
+		{
+			$this->_setTimeout_name = 'setTimeout';
+			$this->_delete_name = 'delete';
+			$this->_ping_success = '+PONG';
+		}
+
 		if (empty($this->_config['save_path']))
 		{
 			log_message('error', 'Session: No Redis save path configured.');
@@ -131,7 +172,7 @@ public function open($save_path, $name)
 	{
 		if (empty($this->_config['save_path']))
 		{
-			return $this->_fail();
+			return $this->_failure;
 		}
 
 		$redis = new Redis();
@@ -150,12 +191,11 @@ public function open($save_path, $name)
 		else
 		{
 			$this->_redis = $redis;
+			$this->php5_validate_id();
 			return $this->_success;
 		}
 
-		$this->php5_validate_id();
-
-		return $this->_fail();
+		return $this->_failure;
 	}
 
 	// ------------------------------------------------------------------------
@@ -185,7 +225,7 @@ public function read($session_id)
 			return $session_data;
 		}
 
-		return $this->_fail();
+		return $this->_failure;
 	}
 
 	// ------------------------------------------------------------------------
@@ -203,21 +243,21 @@ public function write($session_id, $session_data)
 	{
 		if ( ! isset($this->_redis, $this->_lock_key))
 		{
-			return $this->_fail();
+			return $this->_failure;
 		}
 		// Was the ID regenerated?
 		elseif ($session_id !== $this->_session_id)
 		{
 			if ( ! $this->_release_lock() OR ! $this->_get_lock($session_id))
 			{
-				return $this->_fail();
+				return $this->_failure;
 			}
 
 			$this->_key_exists = FALSE;
 			$this->_session_id = $session_id;
 		}
 
-		$this->_redis->setTimeout($this->_lock_key, 300);
+		$this->_redis->{$this->_setTimeout_name}($this->_lock_key, 300);
 		if ($this->_fingerprint !== ($fingerprint = md5($session_data)) OR $this->_key_exists === FALSE)
 		{
 			if ($this->_redis->set($this->_key_prefix.$session_id, $session_data, $this->_config['expiration']))
@@ -227,12 +267,12 @@ public function write($session_id, $session_data)
 				return $this->_success;
 			}
 
-			return $this->_fail();
+			return $this->_failure;
 		}
 
-		return ($this->_redis->setTimeout($this->_key_prefix.$session_id, $this->_config['expiration']))
+		return ($this->_redis->{$this->_setTimeout_name}($this->_key_prefix.$session_id, $this->_config['expiration']))
 			? $this->_success
-			: $this->_fail();
+			: $this->_failure;
 	}
 
 	// ------------------------------------------------------------------------
@@ -249,12 +289,12 @@ public function close()
 		if (isset($this->_redis))
 		{
 			try {
-				if ($this->_redis->ping() === '+PONG')
+				if ($this->_redis->ping() === $this->_ping_success)
 				{
 					$this->_release_lock();
 					if ($this->_redis->close() === FALSE)
 					{
-						return $this->_fail();
+						return $this->_failure;
 					}
 				}
 			}
@@ -284,16 +324,16 @@ public function destroy($session_id)
 	{
 		if (isset($this->_redis, $this->_lock_key))
 		{
-			if (($result = $this->_redis->delete($this->_key_prefix.$session_id)) !== 1)
+			if (($result = $this->_redis->{$this->_delete_name}($this->_key_prefix.$session_id)) !== 1)
 			{
-				log_message('debug', 'Session: Redis::delete() expected to return 1, got '.var_export($result, TRUE).' instead.');
+				log_message('debug', 'Session: Redis::'.$this->_delete_name.'() expected to return 1, got '.var_export($result, TRUE).' instead.');
 			}
 
 			$this->_cookie_destroy();
 			return $this->_success;
 		}
 
-		return $this->_fail();
+		return $this->_failure;
 	}
 
 	// ------------------------------------------------------------------------
@@ -345,7 +385,7 @@ protected function _get_lock($session_id)
 		// correct session ID.
 		if ($this->_lock_key === $this->_key_prefix.$session_id.':lock')
 		{
-			return $this->_redis->setTimeout($this->_lock_key, 300);
+			return $this->_redis->{$this->_setTimeout_name}($this->_lock_key, 300);
 		}
 
 		// 30 attempts to obtain a lock, in case another request already has it
@@ -359,11 +399,13 @@ protected function _get_lock($session_id)
 				continue;
 			}
 
-			$result = ($ttl === -2)
-				? $this->_redis->set($lock_key, time(), array('nx', 'ex' => 300))
-				: $this->_redis->setex($lock_key, 300, time());
-
-			if ( ! $result)
+			if ($ttl === -2 && ! $this->_redis->set($lock_key, time(), array('nx', 'ex' => 300)))
+			{
+				// Sleep for 1s to wait for lock releases.
+				sleep(1);
+				continue;
+			}
+			elseif ( ! $this->_redis->setex($lock_key, 300, time()))
 			{
 				log_message('error', 'Session: Error while trying to obtain lock for '.$this->_key_prefix.$session_id);
 				return FALSE;
@@ -401,7 +443,7 @@ protected function _release_lock()
 	{
 		if (isset($this->_redis, $this->_lock_key) && $this->_lock)
 		{
-			if ( ! $this->_redis->delete($this->_lock_key))
+			if ( ! $this->_redis->{$this->_delete_name}($this->_lock_key))
 			{
 				log_message('error', 'Session: Error while trying to free lock for '.$this->_lock_key);
 				return FALSE;