Move execute_worker_task to MonitorInstance

The function is rather general and may of use to other monitor modules.

include/maxscale/monitor.hh

@@ -22,7 +22,7 @@ namespace maxscale
 {
 
 class MonitorInstance : public  MXS_MONITOR_INSTANCE
-                      , protected maxscale::Worker
+                      , private maxscale::Worker
 {
 public:
     MonitorInstance(const MonitorInstance&) = delete;
@@ -112,6 +112,8 @@ public:
     virtual json_t* diagnostics_json() const;
 
 protected:
+    typedef std::function<void ()> GenericFunction;
+
     MonitorInstance(MXS_MONITOR* pMonitor);
 
     const std::string& script() const { return m_script; }
@@ -208,6 +210,16 @@ protected:
      */
     virtual void process_state_changes();
 
+    /**
+     * Execute a task in the worker thread of this monitor.
+     *
+     * @param func The task which should be executed, wrapped in a function object.
+     * @param mode Execution mode. If EXECUTE_AUTO, the function will only return once the task has
+     * been executed. Otherwise, the task will be queued and the function returns immediately.
+     * @return True, if task was sent to the worker
+     */
+    bool execute_worker_task(GenericFunction func, execute_mode_t mode = Worker::EXECUTE_AUTO);
+
     MXS_MONITOR*          m_monitor;  /**< The generic monitor structure. */
     MXS_MONITORED_SERVER* m_master;   /**< Master server */