Make some notes about common usage of pbx_builtin_getvar_helper() that is not

thread-safe.


git-svn-id: http://svn.digium.com/svn/asterisk/trunk@111909 f38db490-d61c-443f-a65b-d21fe96a405b

2 files changed, 26 insertions, 0 deletions

diff --git a/doc/janitor-projects.txt b/doc/janitor-projects.txt
index 9d89ef18c..b111204f0 100644
--- a/doc/janitor-projects.txt
+++ b/doc/janitor-projects.txt
@@ -1,3 +1,15 @@
+ -- There a bunch of places where the result of pbx_builtin_getvar_helper()
+    gets stored and used.  This is not threadsafe.  This code should be replaced
+	with the following thread-safe version:
+
+	const char *var;
+
+	ast_channel_lock(chan);
+	if ((var = pbx_builtin_getvar_helper(chan, "MYVAR"))) {
+		var = ast_strdupa(var);
+	}
+	ast_channel_unlock(chan);
+
  -- Convert all existing uses of astobj.h to astobj2.h
     -- (chan_sip already in progress in a branch)
 
diff --git a/include/asterisk/pbx.h b/include/asterisk/pbx.h
index 1761a9bd7..56bd83fa5 100644
--- a/include/asterisk/pbx.h
+++ b/include/asterisk/pbx.h
@@ -800,6 +800,20 @@ int pbx_builtin_serialize_variables(struct ast_channel *chan, struct ast_str **b
 
 /*!
  * \note Will lock the channel.
+ *
+ * \note This function will return a pointer to the buffer inside the channel
+ * variable.  This value should only be accessed with the channel locked.  If
+ * the value needs to be kept around, it should be done by using the following
+ * thread-safe code:
+ * \code
+ *		const char *var;
+ *
+ *		ast_channel_lock(chan);
+ *		if ((var = pbx_builtin_getvar_helper(chan, "MYVAR"))) {
+ *			var = ast_strdupa(var);
+ *		}
+ *		ast_channel_unlock(chan);
+ * \endcode
  */
 const char *pbx_builtin_getvar_helper(struct ast_channel *chan, const char *name);