Exclude process-specific link & result cache references from serialized Memcached_Data_Object instances.

Should fix seemingly-random bugs due to destructor free()ing local resources by mistake.

classes/Memcached_DataObject.php

@@ -21,7 +21,7 @@ if (!defined('STATUSNET') && !defined('LACONICA')) { exit(1); }
 
 class Memcached_DataObject extends DB_DataObject
 {
-   /**
+    /**
      * Destructor to free global memory resources associated with
      * this data object when it's unset or goes out of scope.
      * DB_DataObject doesn't do this yet by itself.
@@ -35,6 +35,42 @@ class Memcached_DataObject extends DB_DataObject
         }
     }
 
+    /**
+     * Magic function called at serialize() time.
+     *
+     * We use this to drop a couple process-specific references
+     * from DB_DataObject which can cause trouble in future
+     * processes.
+     *
+     * @return array of variable names to include in serialization.
+     */
+    function __sleep()
+    {
+        $vars = array_keys(get_object_vars($this));
+        $skip = array('_DB_resultid', '_link_loaded');
+        return array_diff($vars, $skip);
+    }
+
+    /**
+     * Magic function called at unserialize() time.
+     *
+     * Clean out some process-specific variables which might
+     * be floating around from a previous process's cached
+     * objects.
+     *
+     * Old cached objects may still have them.
+     */
+    function __wakeup()
+    {
+        // Refers to global state info from a previous process.
+        // Clear this out so we don't accidentally break global
+        // state in *this* process.
+        $this->_DB_resultid = null;
+        
+        // We don't have any local DBO refs, so clear these out.
+        $this->_link_loaded = false;
+    }
+
     /**
      * Wrapper for DB_DataObject's static lookup using memcached
      * as backing instead of an in-process cache array.