Also fix query_plans_by_table

[collectd.git] / src / meta_data.c

diff --git a/src/meta_data.c b/src/meta_data.c
index 48dcabc..d220784 100644 (file)
--- a/src/meta_data.c
+++ b/src/meta_data.c
@@ -109,6 +109,8 @@ static meta_entry_t *md_entry_clone (const meta_entry_t *orig) /* {{{ */
     return (NULL);
 
   copy = md_entry_alloc (orig->key);
+  if (copy == NULL)
+    return (NULL);
   copy->type = orig->type;
   if (copy->type == MD_TYPE_STRING)
     copy->value.mv_string = strdup (orig->value.mv_string);
@@ -207,6 +209,17 @@ static meta_entry_t *md_entry_lookup (meta_data_t *md, /* {{{ */
 } /* }}} meta_entry_t *md_entry_lookup */
 
 /*
+ * Each value_list_t*, as it is going through the system, is handled by exactly
+ * one thread. Plugins which pass a value_list_t* to another thread, e.g. the
+ * rrdtool plugin, must create a copy first. The meta data within a
+ * value_list_t* is not thread safe and doesn't need to be.
+ *
+ * The meta data associated with cache entries are a different story. There, we
+ * need to ensure exclusive locking to prevent leaks and other funky business.
+ * This is ensured by the uc_meta_data_get_*() functions.
+ */
+
+/*
  * Public functions
  */
 meta_data_t *meta_data_create (void) /* {{{ */
@@ -250,7 +263,6 @@ void meta_data_destroy (meta_data_t *md) /* {{{ */
   if (md == NULL)
     return;
 
-  pthread_mutex_destroy(&md->lock);
   md_entry_free (md->head);
   pthread_mutex_destroy (&md->lock);
   free (md);