Fix race condition for CEL LINKEDID_END event

This patch fixes to situations that could cause the CEL LINKEDID_END event to
be missed.

1) During a core stop gracefully, modules are unloaded when ast_active_channels
== 0. The LINKDEDID_END event fires during the channel destructor. This means
that occasionally, the cel_* module will be unloaded before the channel is
destroyed. It seemed generally useful to wait until the refcount of all
channels == 0 before unloading, so I added a channel counter and used it in the
shutdown code.

2) During a masquerade, ast_channel_change_linkedid is called. It calls
ast_cel_check_retire_linkedid which unrefs the linkedid in the linkedids
container in cel.c. It didn't ref the new linkedid. Now it does. 

Review: https://reviewboard.asterisk.org/r/1900/
........

Merged revisions 367292 from http://svn.asterisk.org/svn/asterisk/branches/1.8
........

Merged revisions 367299 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@367309 65c4cc65-6c06-0410-ace0-fbb531ad65f3

2 files changed, 13 insertions, 1 deletions

diff --git a/include/asterisk/cel.h b/include/asterisk/cel.h
index b388ffd9b..25a3a4af1 100644
--- a/include/asterisk/cel.h
+++ b/include/asterisk/cel.h
@@ -188,6 +188,15 @@ const char *ast_cel_get_ama_flag_name(enum ast_cel_ama_flag flag);
 void ast_cel_check_retire_linkedid(struct ast_channel *chan);
 
 /*!
+ * \brief Inform CEL that a new linkedid is being used
+ * \since 11
+ *
+ * \retval -1 error
+ * \retval 0 success
+ */
+int ast_cel_linkedid_ref(const char *linkedid);
+
+/*!
  * \brief Create a fake channel from data in a CEL event
  *
  * \note
diff --git a/include/asterisk/channel.h b/include/asterisk/channel.h
index 1a1c99885..59008a6fe 100644
--- a/include/asterisk/channel.h
+++ b/include/asterisk/channel.h
@@ -2104,9 +2104,12 @@ void ast_begin_shutdown(int hangup);
 /*! Cancels an existing shutdown and returns to normal operation */
 void ast_cancel_shutdown(void);
 
-/*! \return number of active/allocated channels */
+/*! \return number of channels available for lookup */
 int ast_active_channels(void);
 
+/*! \return the number of channels not yet destroyed */
+int ast_undestroyed_channels(void);
+
 /*! \return non-zero if Asterisk is being shut down */
 int ast_shutting_down(void);