1 /*
   2  * Copyright (c) 1997, 2008, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 // A PeriodicTask has the sole purpose of executing its task
  26 // function with regular intervals.
  27 // Usage:
  28 //   PeriodicTask pf(10);
  29 //   pf.enroll();
  30 //   ...
  31 //   pf.disenroll();
  32 
  33 class PeriodicTask: public CHeapObj {
  34  public:
  35   // Useful constants.
  36   // The interval constants are used to ensure the declared interval
  37   // is appropriate;  it must be between min_interval and max_interval,
  38   // and have a granularity of interval_gran (all in millis).
  39   enum { max_tasks     = 10,       // Max number of periodic tasks in system
  40          interval_gran = 10,
  41          min_interval  = 10,
  42          max_interval  = 10000 };
  43 
  44   static int num_tasks()   { return _num_tasks; }
  45 
  46  private:
  47   size_t _counter;
  48   const size_t _interval;
  49 
  50   static int _num_tasks;
  51   static PeriodicTask* _tasks[PeriodicTask::max_tasks];
  52   static void real_time_tick(size_t delay_time);
  53 
  54 #ifndef PRODUCT
  55   static elapsedTimer _timer;                      // measures time between ticks
  56   static int _ticks;                               // total number of ticks
  57   static int _intervalHistogram[max_interval];     // to check spacing of timer interrupts
  58  public:
  59   static void print_intervals();
  60 #endif
  61   // Only the WatcherThread can cause us to execute PeriodicTasks
  62   friend class WatcherThread;
  63  public:
  64   PeriodicTask(size_t interval_time); // interval is in milliseconds of elapsed time
  65   ~PeriodicTask();
  66 
  67   // Tells whether is enrolled
  68   bool is_enrolled() const;
  69 
  70   // Make the task active
  71   // NOTE: this may only be called before the WatcherThread has been started
  72   void enroll();
  73 
  74   // Make the task deactive
  75   // NOTE: this may only be called either while the WatcherThread is
  76   // inactive or by a task from within its task() method. One-shot or
  77   // several-shot tasks may be implemented this way.
  78   void disenroll();
  79 
  80   void execute_if_pending(size_t delay_time) {
  81     _counter += delay_time;
  82     if (_counter >= _interval) {
  83       _counter = 0;
  84       task();
  85     }
  86   }
  87 
  88   // Returns how long (time in milliseconds) before the next time we should
  89   // execute this task.
  90   size_t time_to_next_interval() const {
  91     assert(_interval > _counter,  "task counter greater than interval?");
  92     return _interval - _counter;
  93   }
  94 
  95   // Calculate when the next periodic task will fire.
  96   // Called by the WatcherThread's run method.
  97   // This assumes that periodic tasks aren't entering the system
  98   // dynamically, except for during startup.
  99   static size_t time_to_wait() {
 100     if (_num_tasks == 0) {
 101       // Don't wait any more; shut down the thread since we don't
 102       // currently support dynamic enrollment.
 103       return 0;
 104     }
 105 
 106     size_t delay = _tasks[0]->time_to_next_interval();
 107     for (int index = 1; index < _num_tasks; index++) {
 108       delay = MIN2(delay, _tasks[index]->time_to_next_interval());
 109     }
 110     return delay;
 111   }
 112 
 113   // The task to perform at each period
 114   virtual void task() = 0;
 115 };