1 /*
   2  * Copyright (c) 1997, 2012, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   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.
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   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
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  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
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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 
  38 class PeriodicTask: public CHeapObj<mtInternal> {
  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   int _counter;
  53   const int _interval;
  54 
  55   static int _num_tasks;
  56   static PeriodicTask* _tasks[PeriodicTask::max_tasks];
  57   static void real_time_tick(int 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   // Make the task active
  73   // For dynamic enrollment at the time T, the task will execute somewhere
  74   // between T and T + interval_time.
  75   void enroll();
  76 
  77   // Make the task deactive
  78   void disenroll();
  79 
  80   void execute_if_pending(int delay_time) {
  81     // make sure we don't overflow
  82     jlong tmp = (jlong) _counter + (jlong) delay_time;
  83 
  84     if (tmp >= (jlong) _interval) {
  85       _counter = 0;
  86       task();
  87     } else {
  88       _counter += delay_time;
  89     }
  90   }
  91 
  92   // Returns how long (time in milliseconds) before the next time we should
  93   // execute this task.
  94   int time_to_next_interval() const {
  95     assert(_interval > _counter,  "task counter greater than interval?");
  96     return _interval - _counter;
  97   }
  98 
  99   // Calculate when the next periodic task will fire.
 100   // Called by the WatcherThread's run method.
 101   static int time_to_wait();
 102 
 103   // The task to perform at each period
 104   virtual void task() = 0;
 105 };
 106 
 107 #endif // SHARE_VM_RUNTIME_TASK_HPP