[ci skip] Merge pull request #5170 from tianhe1986/develop_session_race_condition

Decreasing the probability of race condition in session lock

1 files changed, 3 insertions, 2 deletions

diff --git a/system/libraries/Session/drivers/Session_memcached_driver.php b/system/libraries/Session/drivers/Session_memcached_driver.php
index 2556bf0f7..5e90539d7 100644
--- a/system/libraries/Session/drivers/Session_memcached_driver.php
+++ b/system/libraries/Session/drivers/Session_memcached_driver.php
@@ -310,7 +310,7 @@ class CI_Session_memcached_driver extends CI_Session_driver implements SessionHa
 			if ( ! $this->_memcached->replace($this->_lock_key, time(), 300))
 			{
 				return ($this->_memcached->getResultCode() === Memcached::RES_NOTFOUND)
-					? $this->_memcached->set($this->_lock_key, time(), 300)
+					? $this->_memcached->add($this->_lock_key, time(), 300)
 					: FALSE;
 			}
 		}
@@ -326,7 +326,8 @@ class CI_Session_memcached_driver extends CI_Session_driver implements SessionHa
 				continue;
 			}
 
-			if ( ! $this->_memcached->set($lock_key, time(), 300))
+			$method = ($this->_memcached->getResultCode() === Memcached::RES_NOTFOUND) ? 'add' : 'set';
+			if ( ! $this->_memcached->$method($lock_key, time(), 300))
 			{
 				log_message('error', 'Session: Error while trying to obtain lock for '.$this->_key_prefix.$session_id);
 				return FALSE;