1 /*
   2  * Copyright (c) 1997, 2015, 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
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  23  */
  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   // Can only be called by the WatcherThread
  58   static void real_time_tick(int delay_time);
  59 
  60 #ifndef PRODUCT
  61   static elapsedTimer _timer;                      // measures time between ticks
  62   static int _ticks;                               // total number of ticks
  63   static int _intervalHistogram[max_interval];     // to check spacing of timer interrupts
  64  public:
  65   static void print_intervals();
  66 #endif
  67   // Only the WatcherThread can cause us to execute PeriodicTasks
  68   friend class WatcherThread;
  69  public:
  70   PeriodicTask(size_t interval_time); // interval is in milliseconds of elapsed time
  71   ~PeriodicTask();
  72 
  73   // Make the task active
  74   // For dynamic enrollment at the time T, the task will execute somewhere
  75   // between T and T + interval_time.
  76   void enroll();
  77 
  78   // Make the task deactive
  79   void disenroll();
  80 
  81   void execute_if_pending(int delay_time) {
  82     // make sure we don't overflow
  83     jlong tmp = (jlong) _counter + (jlong) delay_time;
  84 
  85     if (tmp >= (jlong) _interval) {
  86       _counter = 0;
  87       task();
  88     } else {
  89       _counter += delay_time;
  90     }
  91   }
  92 
  93   // Returns how long (time in milliseconds) before the next time we should
  94   // execute this task.
  95   int 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   // Requires the PeriodicTask_lock.
 103   static int time_to_wait();
 104 
 105   // The task to perform at each period
 106   virtual void task() = 0;
 107 };
 108 
 109 #endif // SHARE_VM_RUNTIME_TASK_HPP
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