Track module use count for res_calendar

If the res_calendar module was followed immediately by one of the
calendar tech modules and "core stop gracefully" was run, Asterisk
would crash.

This patch adds use count tracking for res_calendar so that it is
unloaded after the tech modules when shutting down gracefully. It
is now not possible to unload all the of the calendar modules via
"module unload res_calednar.so", but it is still possible to unload
them all via "module unload -h res_calendar.so".

Review: https://reviewboard.asterisk.org/r/1752/
........

Merged revisions 356291 from http://svn.asterisk.org/svn/asterisk/branches/1.8
........

Merged revisions 356297 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@356314 65c4cc65-6c06-0410-ace0-fbb531ad65f3

include/asterisk/calendar.h

@@ -25,6 +25,7 @@
 #include "asterisk/linkedlists.h"
 #include "asterisk/lock.h"
 #include "asterisk/dial.h"
+#include "asterisk/module.h"
 
 /*! \file calendar.h
  * \brief A general API for managing calendar events with Asterisk
@@ -69,6 +70,7 @@ struct ast_calendar_tech {
 	const char *type;
 	const char *description;
 	const char *module;
+	struct ast_module_user *user;
 	int (* is_busy)(struct ast_calendar *calendar); /*!< Override default busy determination */
 	void *(* load_calendar)(void *data);   /*!< Create private structure, add calendar events, etc. */
 	void *(* unref_calendar)(void *obj);   /*!< Function to be called to free the private structure */

main/loader.c

@@ -239,7 +239,9 @@ void __ast_module_user_hangup_all(struct ast_module *mod)
 
 	AST_LIST_LOCK(&mod->users);
 	while ((u = AST_LIST_REMOVE_HEAD(&mod->users, entry))) {
-		ast_softhangup(u->chan, AST_SOFTHANGUP_APPUNLOAD);
+		if (u->chan) {
+			ast_softhangup(u->chan, AST_SOFTHANGUP_APPUNLOAD);
+		}
 		ast_atomic_fetchadd_int(&mod->usecount, -1);
 		ast_free(u);
 	}

res/res_calendar.c

@@ -532,6 +532,7 @@ int ast_calendar_register(struct ast_calendar_tech *tech)
 		}
 	}
 	AST_LIST_INSERT_HEAD(&techs, tech, list);
+	tech->user = ast_module_user_add(NULL);
 	AST_LIST_UNLOCK(&techs);
 
 	ast_verb(2, "Registered calendar type '%s' (%s)\n", tech->type, tech->description);
@@ -564,6 +565,7 @@ void ast_calendar_unregister(struct ast_calendar_tech *tech)
 		ao2_callback(calendars, OBJ_UNLINK | OBJ_NODATA | OBJ_MULTIPLE, match_caltech_cb, tech);
 
 		AST_LIST_REMOVE_CURRENT(list);
+		ast_module_user_remove(iter->user);
 		ast_verb(2, "Unregistered calendar type '%s'\n", tech->type);
 		break;
 	}