MXS-2218 Add housekeeper functionality to MainWorker

In preparation for moving the housekeeper functionality on top
of MainWorker.

server/core/mainworker.cc

@@ -49,6 +49,41 @@ MainWorker& MainWorker::get()
     return *this_unit.pThis;
 }
 
+void MainWorker::add_task(const char* zName, TASKFN func, void* pData, int frequency)
+{
+    call([=]() {
+            mxb_assert(m_tasks_by_name.find(zName) == m_tasks_by_name.end());
+
+            Task task(zName, func, pData);
+
+            auto p = m_tasks_by_name.insert(std::make_pair(std::string(zName), task));
+            Task& inserted_task = (*p.first).second;
+
+            inserted_task.id = delayed_call(frequency * 1000,
+                                            &MainWorker::call_task,
+                                            this,
+                                            &inserted_task);
+        },
+        EXECUTE_AUTO);
+}
+
+void MainWorker::remove_task(const char* zName)
+{
+    call([this, zName]() {
+            auto it = m_tasks_by_name.find(zName);
+            mxb_assert(it != m_tasks_by_name.end());
+
+            if (it != m_tasks_by_name.end())
+            {
+                MXB_AT_DEBUG(bool cancelled =) cancel_delayed_call(it->second.id);
+                mxb_assert(cancelled);
+
+                m_tasks_by_name.erase(it);
+            }
+        },
+        EXECUTE_AUTO);
+}
+
 bool MainWorker::pre_run()
 {
     return true;
@@ -62,4 +97,28 @@ void MainWorker::epoll_tick()
 {
 }
 
+bool MainWorker::call_task(Worker::Call::action_t action, MainWorker::Task* pTask)
+{
+    bool call_again = false;
+
+    if (action == Worker::Call::EXECUTE)
+    {
+        mxb_assert(m_tasks_by_name.find(pTask->name) != m_tasks_by_name.end());
+
+        call_again = pTask->func(pTask->pData);
+
+        if (!call_again)
+        {
+            auto it = m_tasks_by_name.find(pTask->name);
+
+            if (it != m_tasks_by_name.end()) // Not found, if task function removes task.
+            {
+                m_tasks_by_name.erase(it);
+            }
+        }
+    }
+
+    return call_again;
+}
+
 }