Add mailbox task's factory functions

src/factory/WFTask.h

@@ -620,6 +620,14 @@ public:
 		this->mailbox = mailbox;
 	}
 
+	WFMailboxTask(std::function<void (WFMailboxTask *)>&& cb) :
+		next(&this->user_data),
+		value(2),
+		callback(std::move(cb))
+	{
+		this->mailbox = &this->user_data;
+	}
+
 protected:
 	virtual ~WFMailboxTask() { }
 };

src/factory/WFTaskFactory.cc

@@ -293,6 +293,33 @@ void WFTaskFactory::count_by_name(const std::string& counter_name, unsigned int
 	__CounterMap::get_instance()->count_n(counter_name, n);
 }
 
+/********MailboxTask*************/
+
+class __WFMailboxTask : public WFMailboxTask
+{
+public:
+	__WFMailboxTask(size_t size, mailbox_callback_t&& cb) :
+		WFMailboxTask(new void *[size], size, std::move(cb))
+	{
+	}
+
+	virtual ~__WFMailboxTask()
+	{
+		delete []this->mailbox;
+	}
+};
+
+WFMailboxTask *WFTaskFactory::create_mailbox_task(size_t size,
+												  mailbox_callback_t callback)
+{
+	return new __WFMailboxTask(size, std::move(callback));
+}
+
+WFMailboxTask *WFTaskFactory::create_mailbox_task(mailbox_callback_t callback)
+{
+	return new WFMailboxTask(std::move(callback));
+}
+
 /********FileIOTask*************/
 
 class WFFilepreadTask : public WFFileIOTask

src/factory/WFTaskFactory.h

@@ -90,6 +90,7 @@ using fsync_callback_t = std::function<void (WFFileSyncTask *)>;
 using timer_callback_t = std::function<void (WFTimerTask *)>;
 using counter_callback_t = std::function<void (WFCounterTask *)>;
 
+// Mailbox is like counter with data passing
 using mailbox_callback_t = std::function<void (WFMailboxTask *)>;
 
 // Graph (DAG) task.
@@ -229,6 +230,9 @@ public:
 	static WFMailboxTask *create_mailbox_task(size_t size,
 											  mailbox_callback_t callback);
 
+	/* Use 'user_data' as mailbox. Store only one message. */
+	static WFMailboxTask *create_mailbox_task(mailbox_callback_t callback);
+
 public:
 	template<class FUNC, class... ARGS>
 	static WFGoTask *create_go_task(const std::string& queue_name,