task.hpp

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * 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).
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 * 2 along with this work; if not, write to the Free Software Foundation,
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#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:
  int _counter;
  const int _interval;

  static int _num_tasks;
  static PeriodicTask* _tasks[PeriodicTask::max_tasks];
  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.
  static int time_to_wait();

  // The task to perform at each period
  virtual void task() = 0;
};

#endif // SHARE_VM_RUNTIME_TASK_HPP