Fix #3627: Keep timed locks for more than 5 seconds

Emulated locks for Redis and Memcached now have a TTL
of 300 seconds (the default HTTP request timeout value
on many environments) and 30 attemps, each separated by
sleep(1), are made by the blocked request to try and
obtain a lock if it has been freed.

Additionaly, the blocking time for MySQL's locks,
which are also timed, is also set to 300 seconds.

4 files changed, 25 insertions, 53 deletions

diff --git a/system/libraries/Session/drivers/Session_database_driver.php b/system/libraries/Session/drivers/Session_database_driver.php
index f496b4fe0..76c1cf34e 100644
--- a/system/libraries/Session/drivers/Session_database_driver.php
+++ b/system/libraries/Session/drivers/Session_database_driver.php
@@ -319,7 +319,7 @@ class CI_Session_database_driver extends CI_Session_driver implements SessionHan
 		if ($this->_platform === 'mysql')
 		{
 			$arg = $session_id.($this->_config['match_ip'] ? '_'.$_SERVER['REMOTE_ADDR'] : '');
-			if ($this->_db->query("SELECT GET_LOCK('".$arg."', 10) AS ci_session_lock")->row()->ci_session_lock)
+			if ($this->_db->query("SELECT GET_LOCK('".$arg."', 300) AS ci_session_lock")->row()->ci_session_lock)
 			{
 				$this->_lock = $arg;
 				return TRUE;
diff --git a/system/libraries/Session/drivers/Session_memcached_driver.php b/system/libraries/Session/drivers/Session_memcached_driver.php
index f1a6e2400..938a612d9 100644
--- a/system/libraries/Session/drivers/Session_memcached_driver.php
+++ b/system/libraries/Session/drivers/Session_memcached_driver.php
@@ -204,7 +204,7 @@ class CI_Session_memcached_driver extends CI_Session_driver implements SessionHa
 
 		if (isset($this->_lock_key))
 		{
-			$this->_memcached->replace($this->_lock_key, time(), 5);
+			$this->_memcached->replace($this->_lock_key, time(), 300);
 			if ($this->_fingerprint !== ($fingerprint = md5($session_data)))
 			{
 				if ($this->_memcached->set($this->_key_prefix.$session_id, $session_data, $this->_config['expiration']))
@@ -299,34 +299,21 @@ class CI_Session_memcached_driver extends CI_Session_driver implements SessionHa
 	{
 		if (isset($this->_lock_key))
 		{
-			return $this->_memcached->replace($this->_lock_key, time(), 5);
+			return $this->_memcached->replace($this->_lock_key, time(), 300);
 		}
 
+		// 30 attempts to obtain a lock, in case another request already has it
 		$lock_key = $this->_key_prefix.$session_id.':lock';
-		if ( ! ($ts = $this->_memcached->get($lock_key)))
-		{
-			if ( ! $this->_memcached->set($lock_key, TRUE, 5))
-			{
-				log_message('error', 'Session: Error while trying to obtain lock for '.$this->_key_prefix.$session_id);
-				return FALSE;
-			}
-
-			$this->_lock_key = $lock_key;
-			$this->_lock = TRUE;
-			return TRUE;
-		}
-
-		// Another process has the lock, we'll try to wait for it to free itself ...
 		$attempt = 0;
-		while ($attempt++ < 5)
+		do
 		{
-			usleep(((time() - $ts) * 1000000) - 20000);
-			if (($ts = $this->_memcached->get($lock_key)) < time())
+			if ($this->_memcached->get($lock_key))
 			{
+				sleep(1);
 				continue;
 			}
 
-			if ( ! $this->_memcached->set($lock_key, time(), 5))
+			if ( ! $this->_memcached->set($lock_key, time(), 300))
 			{
 				log_message('error', 'Session: Error while trying to obtain lock for '.$this->_key_prefix.$session_id);
 				return FALSE;
@@ -335,8 +322,9 @@ class CI_Session_memcached_driver extends CI_Session_driver implements SessionHa
 			$this->_lock_key = $lock_key;
 			break;
 		}
+		while ($attempt++ < 30);
 
-		if ($attempt === 5)
+		if ($attempt === 30)
 		{
 			log_message('error', 'Session: Unable to obtain lock for '.$this->_key_prefix.$session_id.' after 5 attempts, aborting.');
 			return FALSE;
diff --git a/system/libraries/Session/drivers/Session_redis_driver.php b/system/libraries/Session/drivers/Session_redis_driver.php
index 5fbb5222c..1ce101daf 100644
--- a/system/libraries/Session/drivers/Session_redis_driver.php
+++ b/system/libraries/Session/drivers/Session_redis_driver.php
@@ -205,7 +205,7 @@ class CI_Session_redis_driver extends CI_Session_driver implements SessionHandle
 
 		if (isset($this->_lock_key))
 		{
-			$this->_redis->setTimeout($this->_lock_key, 5);
+			$this->_redis->setTimeout($this->_lock_key, 300);
 			if ($this->_fingerprint !== ($fingerprint = md5($session_data)))
 			{
 				if ($this->_redis->set($this->_key_prefix.$session_id, $session_data, $this->_config['expiration']))
@@ -313,40 +313,21 @@ class CI_Session_redis_driver extends CI_Session_driver implements SessionHandle
 	{
 		if (isset($this->_lock_key))
 		{
-			return $this->_redis->setTimeout($this->_lock_key, 5);
+			return $this->_redis->setTimeout($this->_lock_key, 300);
 		}
 
+		// 30 attempts to obtain a lock, in case another request already has it
 		$lock_key = $this->_key_prefix.$session_id.':lock';
-		if (($ttl = $this->_redis->ttl($lock_key)) < 1)
-		{
-			if ( ! $this->_redis->setex($lock_key, 5, time()))
-			{
-				log_message('error', 'Session: Error while trying to obtain lock for '.$this->_key_prefix.$session_id);
-				return FALSE;
-			}
-
-			$this->_lock_key = $lock_key;
-
-			if ($ttl === -1)
-			{
-				log_message('debug', 'Session: Lock for '.$this->_key_prefix.$session_id.' had no TTL, overriding.');
-			}
-
-			$this->_lock = TRUE;
-			return TRUE;
-		}
-
-		// Another process has the lock, we'll try to wait for it to free itself ...
 		$attempt = 0;
-		while ($attempt++ < 5)
+		do
 		{
-			usleep(($ttl * 1000000) - 20000);
 			if (($ttl = $this->_redis->ttl($lock_key)) > 0)
 			{
+				sleep(1);
 				continue;
 			}
 
-			if ( ! $this->_redis->setex($lock_key, 5, time()))
+			if ( ! $this->_redis->setex($lock_key, 300, time()))
 			{
 				log_message('error', 'Session: Error while trying to obtain lock for '.$this->_key_prefix.$session_id);
 				return FALSE;
@@ -355,12 +336,17 @@ class CI_Session_redis_driver extends CI_Session_driver implements SessionHandle
 			$this->_lock_key = $lock_key;
 			break;
 		}
+		while ($attempt++ < 30);
 
-		if ($attempt === 5)
+		if ($attempt === 30)
 		{
-			log_message('error', 'Session: Unable to obtain lock for '.$this->_key_prefix.$session_id.' after 5 attempts, aborting.');
+			log_message('error', 'Session: Unable to obtain lock for '.$this->_key_prefix.$session_id.' after 30 attempts, aborting.');
 			return FALSE;
 		}
+		elseif ($ttl === -1)
+		{
+			log_message('debug', 'Session: Lock for '.$this->_key_prefix.$session_id.' had no TTL, overriding.');
+		}
 
 		$this->_lock = TRUE;
 		return TRUE;
diff --git a/user_guide_src/source/libraries/sessions.rst b/user_guide_src/source/libraries/sessions.rst
index 9fc33247b..104adb631 100644
--- a/user_guide_src/source/libraries/sessions.rst
+++ b/user_guide_src/source/libraries/sessions.rst
@@ -632,8 +632,7 @@ Redis Driver
 
 .. note:: Since Redis doesn't have a locking mechanism exposed, locks for
 	this driver are emulated by a separate value that is kept for up
-	to 5 seconds. You may experience issues if your page loads take
-	longer than that!
+	to 300 seconds.
 
 Redis is a storage engine typically used for caching and popular because
 of its high performance, which is also probably your reason to use the
@@ -670,8 +669,7 @@ Memcached Driver
 
 .. note:: Since Memcache doesn't have a locking mechanism exposed, locks
 	for this driver are emulated by a separate value that is kept for
-	up to 5 seconds. You may experience issues if your page loads take
-	longer than that!
+	up to 300 seconds.
 
 The 'memcached' driver is very similar to the 'redis' one in all of its
 properties, except perhaps for availability, because PHP's `Memcached