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 };