Fix extension state callback references in chan_sip.

Chan_sip gives a dialog reference to the extension state callback and
assumes that when ast_extension_state_del() returns, the callback cannot
happen anymore.  Chan_sip then reduces the dialog reference count
associated with the callback.  Recent changes (ASTERISK-17760) have
resulted in the potential for the callback to happen after
ast_extension_state_del() has returned.  For chan_sip, this could be very
bad because the dialog pointer could have already been destroyed.

* Added ast_extension_state_add_destroy() so chan_sip can account for the
sip_pvt reference given to the extension state callback when the extension
state callback is deleted.

* Fix pbx.c awkward statecbs handling in ast_extension_state_add_destroy()
and handle_statechange() now that the struct ast_state_cb has a destructor
to call.

* Ensure that ast_extension_state_add_destroy() will never return -1 or 0
for a successful registration.

* Fixed pbx.c statecbs_cmp() to compare the correct information.  The
passed in value to compare is a change_cb function pointer not an object
pointer.

* Make pbx.c ast_merge_contexts_and_delete() not perform callbacks with
AST_EXTENSION_REMOVED with locks held.  Chan_sip is notorious for
deadlocking when those locks are held during the callback.

* Removed unused lock declaration for the pbx.c store_hints list.

(closes issue ASTERISK-18844)
Reported by: rmudgett

Review: https://reviewboard.asterisk.org/r/1635/
........

Merged revisions 348940 from http://svn.asterisk.org/svn/asterisk/branches/1.8
........

Merged revisions 348952 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@348953 65c4cc65-6c06-0410-ace0-fbb531ad65f3

include/asterisk/pbx.h

@@ -78,6 +78,9 @@ struct ast_sw;
 /*! \brief Typedef for devicestate and hint callbacks */
 typedef int (*ast_state_cb_type)(const char *context, const char *exten, enum ast_extension_states state, void *data);
 
+/*! \brief Typedef for devicestate and hint callback removal indication callback */
+typedef void (*ast_state_cb_destroy_type)(int id, void *data);
+
 /*! \brief Data structure associated with a custom dialplan function */
 struct ast_custom_function {
 	const char *name;			/*!< Name */
@@ -407,34 +410,55 @@ int ast_extension_state(struct ast_channel *c, const char *context, const char *
  */
 const char *ast_extension_state2str(int extension_state);
 
+/*!
+ * \brief Registers a state change callback with destructor.
+ * \since 1.8.9
+ * \since 10.1.0
+ *
+ * \param context which context to look in
+ * \param exten which extension to get state
+ * \param change_cb callback to call if state changed
+ * \param destroy_cb callback to call when registration destroyed.
+ * \param data to pass to callback
+ *
+ * \note The change_cb is called if the state of an extension is changed.
+ *
+ * \note The destroy_cb is called when the registration is
+ * deleted so the registerer can release any associated
+ * resources.
+ *
+ * \retval -1 on failure
+ * \retval ID on success
+ */
+int ast_extension_state_add_destroy(const char *context, const char *exten,
+	ast_state_cb_type change_cb, ast_state_cb_destroy_type destroy_cb, void *data);
+
 /*!
  * \brief Registers a state change callback
  *
  * \param context which context to look in
  * \param exten which extension to get state
- * \param callback callback to call if state changed
+ * \param change_cb callback to call if state changed
  * \param data to pass to callback
  *
- * The callback is called if the state of an extension is changed.
+ * \note The change_cb is called if the state of an extension is changed.
  *
  * \retval -1 on failure
  * \retval ID on success
  */
 int ast_extension_state_add(const char *context, const char *exten,
-			    ast_state_cb_type callback, void *data);
+	ast_state_cb_type change_cb, void *data);
 
 /*!
  * \brief Deletes a registered state change callback by ID
  *
- * \param id of the callback to delete
- * \param callback callback
- *
- * Removes the callback from list of callbacks
+ * \param id of the registered state callback to delete
+ * \param change_cb callback to call if state changed (Used if id == 0 (global))
  *
  * \retval 0 success
  * \retval -1 failure
  */
-int ast_extension_state_del(int id, ast_state_cb_type callback);
+int ast_extension_state_del(int id, ast_state_cb_type change_cb);
 
 /*!
  * \brief If an extension hint exists, return non-zero