/*

 * Copyright 1997-2008 Sun Microsystems, Inc.  All Rights Reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

 * have any questions.

 *

 */

// A PeriodicTask has the sole purpose of executing its task

// function with regular intervals.

// Usage:

//   PeriodicTask pf(10);

//   pf.enroll();

//   ...

//   pf.disenroll();

class PeriodicTask: public CHeapObj {

 public:

  // Useful constants.

  // The interval constants are used to ensure the declared interval

  // is appropriate;  it must be between min_interval and max_interval,

  // and have a granularity of interval_gran (all in millis).

  enum { max_tasks     = 10,       // Max number of periodic tasks in system

         interval_gran = 10,

         min_interval  = 10,

         max_interval  = 10000 };

  static int num_tasks()   { return _num_tasks; }

 private:

  size_t _counter;

  const size_t _interval;

  static int _num_tasks;

  static PeriodicTask* _tasks[PeriodicTask::max_tasks];

  static void real_time_tick(size_t delay_time);

#ifndef PRODUCT

  static elapsedTimer _timer;                      // measures time between ticks

  static int _ticks;                               // total number of ticks

  static int _intervalHistogram[max_interval];     // to check spacing of timer interrupts

 public:

  static void print_intervals();

#endif

  // Only the WatcherThread can cause us to execute PeriodicTasks

  friend class WatcherThread;

 public:

  PeriodicTask(size_t interval_time); // interval is in milliseconds of elapsed time

  ~PeriodicTask();

  // Tells whether is enrolled

  bool is_enrolled() const;

  // Make the task active

  // NOTE: this may only be called before the WatcherThread has been started

  void enroll();

  // Make the task deactive

  // NOTE: this may only be called either while the WatcherThread is

  // inactive or by a task from within its task() method. One-shot or

  // several-shot tasks may be implemented this way.

  void disenroll();

  void execute_if_pending(size_t delay_time) {

    _counter += delay_time;

    if (_counter >= _interval) {

      _counter = 0;

      task();

    }

  }

  // Returns how long (time in milliseconds) before the next time we should

  // execute this task.

  size_t time_to_next_interval() const {

    assert(_interval > _counter,  "task counter greater than interval?");

    return _interval - _counter;

  }

  // Calculate when the next periodic task will fire.

  // Called by the WatcherThread's run method.

  // This assumes that periodic tasks aren't entering the system

  // dynamically, except for during startup.

  static size_t time_to_wait() {

    if (_num_tasks == 0) {

      // Don't wait any more; shut down the thread since we don't

      // currently support dynamic enrollment.

      return 0;

    }

    size_t delay = _tasks[0]->time_to_next_interval();

    for (int index = 1; index < _num_tasks; index++) {

      delay = MIN2(delay, _tasks[index]->time_to_next_interval());

    }

    return delay;

  }

  // The task to perform at each period

  virtual void task() = 0;

};