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1 /*
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196
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2 * Copyright 1997-2008 Sun Microsystems, Inc. All Rights Reserved.
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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4 *
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5 * This code is free software; you can redistribute it and/or modify it
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6 * under the terms of the GNU General Public License version 2 only, as
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7 * published by the Free Software Foundation.
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8 *
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9 * This code is distributed in the hope that it will be useful, but WITHOUT
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10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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12 * version 2 for more details (a copy is included in the LICENSE file that
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13 * accompanied this code).
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14 *
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15 * You should have received a copy of the GNU General Public License version
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16 * 2 along with this work; if not, write to the Free Software Foundation,
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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18 *
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19 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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20 * CA 95054 USA or visit www.sun.com if you need additional information or
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21 * have any questions.
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22 *
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23 */
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24
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25 // A PeriodicTask has the sole purpose of executing its task
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26 // function with regular intervals.
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27 // Usage:
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28 // PeriodicTask pf(10);
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29 // pf.enroll();
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30 // ...
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31 // pf.disenroll();
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32
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33 class PeriodicTask: public CHeapObj {
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34 public:
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35 // Useful constants.
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36 // The interval constants are used to ensure the declared interval
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37 // is appropriate; it must be between min_interval and max_interval,
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38 // and have a granularity of interval_gran (all in millis).
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39 enum { max_tasks = 10, // Max number of periodic tasks in system
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40 interval_gran = 10,
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41 min_interval = 10,
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42 max_interval = 10000 };
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43
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44 static int num_tasks() { return _num_tasks; }
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45
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46 private:
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47 size_t _counter;
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48 const size_t _interval;
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49
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50 static int _num_tasks;
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51 static PeriodicTask* _tasks[PeriodicTask::max_tasks];
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52 static void real_time_tick(size_t delay_time);
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53
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54 #ifndef PRODUCT
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55 static elapsedTimer _timer; // measures time between ticks
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56 static int _ticks; // total number of ticks
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57 static int _intervalHistogram[max_interval]; // to check spacing of timer interrupts
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58 public:
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59 static void print_intervals();
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60 #endif
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61 // Only the WatcherThread can cause us to execute PeriodicTasks
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62 friend class WatcherThread;
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63 public:
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64 PeriodicTask(size_t interval_time); // interval is in milliseconds of elapsed time
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65 ~PeriodicTask();
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66
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67 // Tells whether is enrolled
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68 bool is_enrolled() const;
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69
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70 // Make the task active
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71 // NOTE: this may only be called before the WatcherThread has been started
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72 void enroll();
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73
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74 // Make the task deactive
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75 // NOTE: this may only be called either while the WatcherThread is
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76 // inactive or by a task from within its task() method. One-shot or
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77 // several-shot tasks may be implemented this way.
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78 void disenroll();
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79
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80 void execute_if_pending(size_t delay_time) {
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81 _counter += delay_time;
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82 if (_counter >= _interval) {
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83 _counter = 0;
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84 task();
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85 }
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86 }
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87
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88 // Returns how long (time in milliseconds) before the next time we should
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89 // execute this task.
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90 size_t time_to_next_interval() const {
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91 assert(_interval > _counter, "task counter greater than interval?");
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92 return _interval - _counter;
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93 }
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94
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95 // Calculate when the next periodic task will fire.
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96 // Called by the WatcherThread's run method.
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97 // This assumes that periodic tasks aren't entering the system
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98 // dynamically, except for during startup.
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99 static size_t time_to_wait() {
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100 if (_num_tasks == 0) {
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101 // Don't wait any more; shut down the thread since we don't
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102 // currently support dynamic enrollment.
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103 return 0;
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104 }
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105
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106 size_t delay = _tasks[0]->time_to_next_interval();
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107 for (int index = 1; index < _num_tasks; index++) {
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108 delay = MIN2(delay, _tasks[index]->time_to_next_interval());
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109 }
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110 return delay;
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111 }
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112
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113 // The task to perform at each period
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114 virtual void task() = 0;
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115 };
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