Code comment and style cleanups to MysqlLockManager

Change-Id: Idf05c0c44f5f6fbb373625c0aebe015e385700ce

diff --git a/includes/filebackend/lockmanager/MySqlLockManager.php b/includes/filebackend/lockmanager/MySqlLockManager.php
index 441ffea..f4ff71e 100644 (file)
--- a/includes/filebackend/lockmanager/MySqlLockManager.php
+++ b/includes/filebackend/lockmanager/MySqlLockManager.php
@@ -2,7 +2,11 @@
 /**
  * MySQL version of DBLockManager that supports shared locks.
  *
- * All lock servers must have the innodb table defined in locking/filelocks.sql.
+ * Do NOT use this on connection handles that are also being used for anything
+ * else as the transaction isolation will be wrong and all the other changes will
+ * get rolled back when the locks release!
+ *
+ * All lock servers must have the innodb table defined in maintenance/locking/filelocks.sql.
  * All locks are non-blocking, which avoids deadlocks.
  *
  * @ingroup LockManager
@@ -46,7 +50,7 @@ class MySqlLockManager extends DBLockManager {
                        $keys[] = $key;
                        $data[] = [ 'fls_key' => $key, 'fls_session' => $this->session ];
                        if ( !isset( $this->locksHeld[$path][self::LOCK_EX] ) ) {
-                               $checkEXKeys[] = $key;
+                               $checkEXKeys[] = $key; // this has no EX lock on $key itself
                        }
                }
 
@@ -54,13 +58,16 @@ class MySqlLockManager extends DBLockManager {
                $db->insert( 'filelocks_shared', $data, __METHOD__, [ 'IGNORE' ] );
                # Actually do the locking queries...
                if ( $type == self::LOCK_SH ) { // reader locks
-                       $blocked = false;
                        # Bail if there are any existing writers...
                        if ( count( $checkEXKeys ) ) {
-                               $blocked = $db->selectField( 'filelocks_exclusive', '1',
+                               $blocked = $db->selectField(
+                                       'filelocks_exclusive',
+                                       '1',
                                        [ 'fle_key' => $checkEXKeys ],
                                        __METHOD__
                                );
+                       } else {
+                               $blocked = false;
                        }
                        # Other prospective writers that haven't yet updated filelocks_exclusive
                        # will recheck filelocks_shared after doing so and bail due to this entry.
@@ -69,7 +76,9 @@ class MySqlLockManager extends DBLockManager {
                        # Bail if there are any existing writers...
                        # This may detect readers, but the safe check for them is below.
                        # Note: if two writers come at the same time, both bail :)
-                       $blocked = $db->selectField( 'filelocks_shared', '1',
+                       $blocked = $db->selectField(
+                               'filelocks_shared',
+                               '1',
                                [ 'fls_key' => $keys, "fls_session != $encSession" ],
                                __METHOD__
                        );
@@ -82,7 +91,9 @@ class MySqlLockManager extends DBLockManager {
                                # Block new readers/writers...
                                $db->insert( 'filelocks_exclusive', $data, __METHOD__ );
                                # Bail if there are any existing readers...
-                               $blocked = $db->selectField( 'filelocks_shared', '1',
+                               $blocked = $db->selectField(
+                                       'filelocks_shared',
+                                       '1',
                                        [ 'fls_key' => $keys, "fls_session != $encSession" ],
                                        __METHOD__
                                );