task.hpp revision 1879:f95d63e2154a 
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24
25#ifndef SHARE_VM_RUNTIME_TASK_HPP
26#define SHARE_VM_RUNTIME_TASK_HPP
27
28#include "utilities/top.hpp"
29
30// A PeriodicTask has the sole purpose of executing its task
31// function with regular intervals.
32// Usage:
33//   PeriodicTask pf(10);
34//   pf.enroll();
35//   ...
36//   pf.disenroll();
37
38class PeriodicTask: public CHeapObj {
39 public:
40  // Useful constants.
41  // The interval constants are used to ensure the declared interval
42  // is appropriate;  it must be between min_interval and max_interval,
43  // and have a granularity of interval_gran (all in millis).
44  enum { max_tasks     = 10,       // Max number of periodic tasks in system
45         interval_gran = 10,
46         min_interval  = 10,
47         max_interval  = 10000 };
48
49  static int num_tasks()   { return _num_tasks; }
50
51 private:
52  size_t _counter;
53  const size_t _interval;
54
55  static int _num_tasks;
56  static PeriodicTask* _tasks[PeriodicTask::max_tasks];
57  static void real_time_tick(size_t delay_time);
58
59#ifndef PRODUCT
60  static elapsedTimer _timer;                      // measures time between ticks
61  static int _ticks;                               // total number of ticks
62  static int _intervalHistogram[max_interval];     // to check spacing of timer interrupts
63 public:
64  static void print_intervals();
65#endif
66  // Only the WatcherThread can cause us to execute PeriodicTasks
67  friend class WatcherThread;
68 public:
69  PeriodicTask(size_t interval_time); // interval is in milliseconds of elapsed time
70  ~PeriodicTask();
71
72  // Tells whether is enrolled
73  bool is_enrolled() const;
74
75  // Make the task active
76  // NOTE: this may only be called before the WatcherThread has been started
77  void enroll();
78
79  // Make the task deactive
80  // NOTE: this may only be called either while the WatcherThread is
81  // inactive or by a task from within its task() method. One-shot or
82  // several-shot tasks may be implemented this way.
83  void disenroll();
84
85  void execute_if_pending(size_t delay_time) {
86    _counter += delay_time;
87    if (_counter >= _interval) {
88      _counter = 0;
89      task();
90    }
91  }
92
93  // Returns how long (time in milliseconds) before the next time we should
94  // execute this task.
95  size_t time_to_next_interval() const {
96    assert(_interval > _counter,  "task counter greater than interval?");
97    return _interval - _counter;
98  }
99
100  // Calculate when the next periodic task will fire.
101  // Called by the WatcherThread's run method.
102  // This assumes that periodic tasks aren't entering the system
103  // dynamically, except for during startup.
104  static size_t time_to_wait() {
105    if (_num_tasks == 0) {
106      // Don't wait any more; shut down the thread since we don't
107      // currently support dynamic enrollment.
108      return 0;
109    }
110
111    size_t delay = _tasks[0]->time_to_next_interval();
112    for (int index = 1; index < _num_tasks; index++) {
113      delay = MIN2(delay, _tasks[index]->time_to_next_interval());
114    }
115    return delay;
116  }
117
118  // The task to perform at each period
119  virtual void task() = 0;
120};
121
122#endif // SHARE_VM_RUNTIME_TASK_HPP
123