MXS-1392 Re-introduce zombie queue

- Extend Worker interface so that zombies can be registered
- Call deletion function at the end of event loop

server/core/maxscale/worker.hh

@@ -14,6 +14,7 @@
 
 #include <maxscale/cppdefs.hh>
 #include <memory>
+#include <vector>
 #include <maxscale/platform.h>
 #include <maxscale/session.h>
 #include <maxscale/utils.hh>
@@ -67,10 +68,11 @@ class Worker : public MXS_WORKER
     Worker& operator = (const Worker&);
 
 public:
-    typedef WORKER_STATISTICS STATISTICS;
-    typedef WorkerTask Task;
-    typedef WorkerDisposableTask DisposableTask;
+    typedef WORKER_STATISTICS     STATISTICS;
+    typedef WorkerTask            Task;
+    typedef WorkerDisposableTask  DisposableTask;
     typedef Registry<MXS_SESSION> SessionsById;
+    typedef std::vector<DCB*>     Zombies;
 
     enum state_t
     {
@@ -226,6 +228,15 @@ public:
      */
     static bool remove_shared_fd(int fd);
 
+    /**
+     * Register zombie for later deletion.
+     *
+     * @param pZombie  DCB that will be deleted at end of event loop.
+     *
+     * @note The DCB must be owned by this worker.
+     */
+    void register_zombie(DCB* pZombie);
+
     /**
      * Main function of worker.
      *
@@ -483,6 +494,8 @@ private:
 
     static Worker* create(int id, int epoll_listener_fd);
 
+    void delete_zombies();
+
     bool post_disposable(DisposableTask* pTask, enum execute_mode_t mode = EXECUTE_AUTO);
 
     void handle_message(MessageQueue& queue, const MessageQueue::Message& msg); // override
@@ -509,6 +522,7 @@ private:
                                          *  worker and not e.g. listener sessions. For now,
                                          *  it's up to the protocol to decide whether a new
                                          *  session is added to the map. */
+    Zombies       m_zombies;            /*< DCBs to be deleted. */
 };
 
 }

server/core/worker.cc

@@ -836,6 +836,19 @@ json_t* mxs_worker_list_to_json(const char* host)
     return task.resource();
 }
 
+void Worker::register_zombie(DCB* pDcb)
+{
+    ss_dassert(pDcb->poll.thread.id == m_id);
+
+    m_zombies.push_back(pDcb);
+}
+
+void Worker::delete_zombies()
+{
+    // TODO: for_each(m_zombies.begin(), m_zombies.end(), dcb_free_all_memory);
+    m_zombies.resize(0);
+}
+
 void Worker::run()
 {
     this_thread.current_worker_id = m_id;
@@ -1227,6 +1240,8 @@ void Worker::poll_waitevents()
 
         m_state = ZPROCESSING;
 
+        delete_zombies();
+
         m_state = IDLE;
     } /*< while(1) */