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hotspot/src/share/vm/runtime/task.hpp

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+/*
+ * Copyright 1997-2007 Sun Microsystems, Inc.  All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ *
+ */
+
+// A PeriodicTask has the sole purpose of executing its task
+// function with regular intervals.
+// Usage:
+//   PeriodicTask pf(10);
+//   pf.enroll();
+//   ...
+//   pf.disenroll();
+
+class PeriodicTask: public CHeapObj {
+ public:
+  // Useful constants.
+  // The interval constants are used to ensure the declared interval
+  // is appropriate;  it must be between min_interval and max_interval,
+  // and have a granularity of interval_gran (all in millis).
+  enum { max_tasks     = 10,       // Max number of periodic tasks in system
+         interval_gran = 10,
+         min_interval  = 10,
+         max_interval  = 10000 };
+
+  static int num_tasks()   { return _num_tasks; }
+
+ private:
+  size_t _counter;
+  const size_t _interval;
+
+  static int _num_tasks;
+  static PeriodicTask* _tasks[PeriodicTask::max_tasks];
+  static void real_time_tick(size_t delay_time);
+
+#ifndef PRODUCT
+  static elapsedTimer _timer;                      // measures time between ticks
+  static int _ticks;                               // total number of ticks
+  static int _intervalHistogram[max_interval];     // to check spacing of timer interrupts
+ public:
+  static void print_intervals();
+#endif
+  // Only the WatcherThread can cause us to execute PeriodicTasks
+  friend class WatcherThread;
+ public:
+  PeriodicTask(size_t interval_time); // interval is in milliseconds of elapsed time
+  ~PeriodicTask();
+
+  // Tells whether is enrolled
+  bool is_enrolled() const;
+
+  // Make the task active
+  // NOTE: this may only be called before the WatcherThread has been started
+  void enroll();
+
+  // Make the task deactive
+  // NOTE: this may only be called either while the WatcherThread is
+  // inactive or by a task from within its task() method. One-shot or
+  // several-shot tasks may be implemented this way.
+  void disenroll();
+
+  void execute_if_pending(size_t delay_time) {
+    _counter += delay_time;
+    if (_counter >= _interval) {
+      _counter = 0;
+      task();
+    }
+  }
+
+  // Returns how long (time in milliseconds) before the next time we should
+  // execute this task.
+  size_t time_to_next_interval() const {
+    assert(_interval > _counter,  "task counter greater than interval?");
+    return _interval - _counter;
+  }
+
+  // Calculate when the next periodic task will fire.
+  // Called by the WatcherThread's run method.
+  // This assumes that periodic tasks aren't entering the system
+  // dynamically, except for during startup.
+  static size_t time_to_wait() {
+    if (_num_tasks == 0) {
+      // Don't wait any more; shut down the thread since we don't
+      // currently support dynamic enrollment.
+      return 0;
+    }
+
+    size_t delay = _tasks[0]->time_to_next_interval();
+    for (int index = 1; index < _num_tasks; index++) {
+      delay = MIN2(delay, _tasks[index]->time_to_next_interval());
+    }
+    return delay;
+  }
+
+  // The task to perform at each period
+  virtual void task() = 0;
+};
+
+class TimeMillisUpdateTask : public PeriodicTask {
+ private:
+  static TimeMillisUpdateTask* _task;
+ public:
+  TimeMillisUpdateTask(int interval) : PeriodicTask(interval) {}
+  void task();
+  static void engage();
+  static void disengage();
+};