AP_Mission: add singleton

libraries/AP_Mission/AP_Mission.cpp

@@ -1768,3 +1768,15 @@ const char *AP_Mission::Mission_Command::type() const {
         return "?";
     }
 }
+
+// singleton instance
+AP_Mission *AP_Mission::_singleton;
+
+namespace AP {
+
+AP_Mission *mission()
+{
+    return AP_Mission::get_singleton();
+}
+
+}

libraries/AP_Mission/AP_Mission.h

@@ -291,6 +291,13 @@ public:
         _prev_nav_cmd_wp_index(AP_MISSION_CMD_INDEX_NONE),
         _last_change_time_ms(0)
     {
+#if CONFIG_HAL_BOARD == HAL_BOARD_SITL
+        if (_singleton != nullptr) {
+            AP_HAL::panic("Mission must be singleton");
+        }
+#endif
+        _singleton = this;
+
         // load parameter defaults
         AP_Param::setup_object_defaults(this, var_info);
 
@@ -304,6 +311,11 @@ public:
         _flags.do_cmd_loaded = false;
     }
 
+    // get singleton instance
+    static AP_Mission *get_singleton() {
+        return _singleton;
+    }
+
     /* Do not allow copies */
     AP_Mission(const AP_Mission &other) = delete;
     AP_Mission &operator=(const AP_Mission&) = delete;    
@@ -470,6 +482,8 @@ public:
     static const struct AP_Param::GroupInfo var_info[];
 
 private:
+    static AP_Mission *_singleton;
+
     static StorageAccess _storage;
 
     struct Mission_Flags {
@@ -563,3 +577,7 @@ private:
     // const functions
     static HAL_Semaphore_Recursive _rsem;
 };
+
+namespace AP {
+    AP_Mission *mission();
+};