vm/runtime/task.hpp

	task.hpp revision 3863
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0N/A
1879N/A#ifndef SHARE_VM_RUNTIME_TASK_HPP
1879N/A#define SHARE_VM_RUNTIME_TASK_HPP
1879N/A
1879N/A#include "utilities/top.hpp"
1879N/A
0N/A// A PeriodicTask has the sole purpose of executing its task
0N/A// function with regular intervals.
0N/A// Usage:
0N/A//   PeriodicTask pf(10);
0N/A//   pf.enroll();
0N/A//   ...
0N/A//   pf.disenroll();
0N/A
0N/Aclass PeriodicTask: public CHeapObj<mtInternal> {
0N/A public:
0N/A  // Useful constants.
0N/A  // The interval constants are used to ensure the declared interval
0N/A  // is appropriate;  it must be between min_interval and max_interval,
0N/A  // and have a granularity of interval_gran (all in millis).
1879N/A  enum { max_tasks     = 10,       // Max number of periodic tasks in system
1879N/A         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