/*

 * Copyright (c) 1997, 2015, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 */

#ifndef SHARE_VM_RUNTIME_TASK_HPP

#define SHARE_VM_RUNTIME_TASK_HPP

#include "memory/allocation.hpp"

#include "runtime/timer.hpp"

// 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<mtInternal> {

 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:

  int _counter;

  const int _interval;

  static int _num_tasks;

  static PeriodicTask* _tasks[PeriodicTask::max_tasks];

  // Can only be called by the WatcherThread

  static void real_time_tick(int 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();

  // Make the task active

  // For dynamic enrollment at the time T, the task will execute somewhere

  // between T and T + interval_time.

  void enroll();

  // Make the task deactive

  void disenroll();

  void execute_if_pending(int delay_time) {

    // make sure we don't overflow

    jlong tmp = (jlong) _counter + (jlong) delay_time;

    if (tmp >= (jlong) _interval) {

      _counter = 0;

      task();

    } else {

      _counter += delay_time;

    }

  }

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

  // execute this task.

  int 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.

  // Requires the PeriodicTask_lock.

  static int time_to_wait();

  // The task to perform at each period

  virtual void task() = 0;

};

#endif // SHARE_VM_RUNTIME_TASK_HPP