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 /*

  * Copyright (c) 1997, 2012, 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

  * or visit www.oracle.com if you need additional information or have any

  * questions.

  *

  */

 #ifndef SHARE_VM_RUNTIME_TASK_HPP

 #define SHARE_VM_RUNTIME_TASK_HPP

 #include "utilities/top.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:

   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;

 };

 #endif // SHARE_VM_RUNTIME_TASK_HPP