Move execute_worker_task into mxs::Worker

The function has use outside of the monitors as it makes execution of
worker tasks much more convenient. Currently, this change only moves the
code and takes it into use: there should be no functional changes.

server/core/worker.cc

@@ -477,6 +477,51 @@ bool Worker::post_disposable(DisposableTask* pTask, enum execute_mode_t mode)
     return posted;
 }
 
+bool Worker::post(GenericFunction func, Semaphore* pSem, execute_mode_t mode)
+{
+
+    class CustomTask : public maxscale::WorkerTask
+    {
+    public:
+
+        CustomTask(GenericFunction func)
+            : m_func(func)
+        {
+        }
+
+    private:
+        GenericFunction m_func;
+
+        void execute(maxscale::Worker& worker)
+        {
+            m_func();
+
+            // The task needs to delete itself only after the task has been executed
+            delete this;
+        }
+    };
+
+    bool rval = false;
+    CustomTask* task = new (std::nothrow) CustomTask(func);
+
+    if (task)
+    {
+        if (!(rval = post(task, pSem, mode)))
+        {
+            // Posting the task failed, it needs to be deleted now
+            delete task;
+        }
+    }
+
+    return rval;
+}
+
+bool Worker::execute(GenericFunction func)
+{
+    Semaphore sem;
+    return post(func, &sem, EXECUTE_AUTO) && sem.wait();
+}
+
 bool Worker::post_message(uint32_t msg_id, intptr_t arg1, intptr_t arg2)
 {
     // NOTE: No logging here, this function must be signal safe.