add Chapter 15 - runtime observer implementation

Chapter15/observer/libs/etl/include/etl/task.h

@@ -0,0 +1,129 @@
+/******************************************************************************
+The MIT License(MIT)
+
+Embedded Template Library.
+https://github.com/ETLCPP/etl
+https://www.etlcpp.com
+
+Copyright(c) 2017 John Wellbelove
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files(the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and / or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions :
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+******************************************************************************/
+
+#ifndef ETL_TASK_INCLUDED
+#define ETL_TASK_INCLUDED
+
+#include "platform.h"
+#include "error_handler.h"
+#include "exception.h"
+
+#include <stdint.h>
+
+namespace etl
+{
+  //***************************************************************************
+  /// Base exception class for task.
+  //***************************************************************************
+  class task_exception : public etl::exception
+  {
+  public:
+
+    task_exception(string_type reason_, string_type file_name_, numeric_type line_number_)
+      : etl::exception(reason_, file_name_, line_number_)
+    {
+    }
+  };
+
+  typedef uint_least8_t task_priority_t;
+
+  //***************************************************************************
+  /// Task.
+  //***************************************************************************
+  class task
+  {
+  public:
+
+    //*******************************************
+    /// Constructor.
+    //*******************************************
+    task(task_priority_t priority)
+      : task_running(true),
+        task_priority(priority)
+    {
+    }
+
+    //*******************************************
+    /// Destructor.
+    //*******************************************
+    virtual ~task()
+    {
+    }
+
+    //*******************************************
+    /// Called to check if the task has work.
+    /// Returns a score as to the amount of work it has to do.
+    //*******************************************
+    virtual uint32_t task_request_work() const = 0;
+
+    //*******************************************
+    /// Called to get the task to do work.
+    //*******************************************
+    virtual void task_process_work() = 0;
+
+    //*******************************************
+    /// Called when the task has been added to the scheduler.
+    //*******************************************
+    virtual void on_task_added()
+    {
+      // Do nothing.
+    }
+
+    //*******************************************
+    /// Set the running state for the task.
+    //*******************************************
+    void set_task_running(bool task_running_)
+    {
+      task_running = task_running_;
+    }
+
+    //*******************************************
+    /// Get the running state for the task.
+    //*******************************************
+    bool task_is_running() const
+    {
+      return task_running;
+    }
+
+    //*******************************************
+    /// Get the priority of the task.
+    /// Higher value = higher priority.
+    //*******************************************
+    etl::task_priority_t get_task_priority() const
+    {
+      return task_priority;
+    }
+
+  private:
+
+    bool task_running;
+    etl::task_priority_t task_priority;
+  };
+}
+
+#endif