Index: includes/cache.inc
===================================================================
RCS file: /cvs/drupal-contrib/contributions/modules/views/includes/cache.inc,v
retrieving revision 1.25.2.4
diff -u -p -r1.25.2.4 cache.inc
--- includes/cache.inc	12 Mar 2010 01:51:47 -0000	1.25.2.4
+++ includes/cache.inc	24 Dec 2010 05:38:49 -0000
@@ -102,18 +102,61 @@ function _views_discover_default_views()
   if (!isset($cache)) {
     $index = views_cache_get('views_default_views_index', TRUE);
 
+    $rebuild_cache = TRUE;
+    $lock_name = __FUNCTION__;
     // Retrieve each cached default view
-    if (isset($index->data) && is_array($index->data)) {
+    if ($index->data && is_array($index->data)) {
+      $rebuild_cache = FALSE;
       $cache = array();
       foreach ($index->data as $view_name) {
-        $data = views_cache_get('views_default:' . $view_name, TRUE);
-        if (isset($data->data) && is_object($data->data)) {
+        $cid = 'views_default:' . $view_name;
+        if ($cached = views_cache_get($cid, TRUE)) {
           $cache[$view_name] = $data->data;
         }
+        else {
+          // As soon as there is a cache miss on one item, try to acquire a
+          // lock.
+          if (!$lock_acquired = lock_acquire($lock_name)) {
+            lock_wait($lock_name);
+            // After waiting, try to fetch the default view from cache again.
+            // If available another process may have rebuilt it, so do not
+            // attempt to rebuild the cache.
+            if ($cached = views_cache_get($cid, TRUE)) {
+              $cache[$view_name] = $data->data;
+            }
+            // If the item is still not in the cache, try to acquire the lock
+            // again and rebuild the cache.
+            else {
+              $lock_acquired = lock_acquire($lock_name);
+              $rebuild_cache = TRUE;
+              break;
+            }
+          }
+          // If the lock was acquired, always rebuild the cache.
+          else {
+            $rebuild_cache = TRUE;
+            break;
+          }
+        }
       }
     }
-    // If missing index, rebuild the cache
     else {
+      if (!$lock_acquired = lock_acquire($lock_name)) {
+        lock_wait();
+        if ($cached = views_cache_get('views_default_views_index', TRUE)) {
+          // Another process has rebuilt the cache while we waited. Re-run the
+          // function to avoid a full cache rebuild.
+          _views_discover_default_views();
+        }
+        else {
+          // Try to re-acquire the lock and re-build the cache either way.
+          lock_acquire($lock_name);
+          $rebuild_cache = TRUE;
+        }
+      }
+    }
+    // Rebuild the cache if necessary.
+    if ($rebuild_cache) {
       views_include_default_views();
       $cache = array();
 
@@ -147,6 +190,7 @@ function _views_discover_default_views()
       foreach ($cache as $name => $view) {
         views_cache_set('views_default:' . $name, $view, TRUE);
       }
+      lock_release($lock_name);
     }
   }