src/hotspot/share/runtime/task.hpp
author erikj
Tue, 12 Sep 2017 19:03:39 +0200
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/*
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 * Copyright (c) 1997, 2015, Oracle and/or its affiliates. All rights reserved.
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 *
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 * This code is free software; you can redistribute it and/or modify it
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 * under the terms of the GNU General Public License version 2 only, as
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 * published by the Free Software Foundation.
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 *
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 * This code is distributed in the hope that it will be useful, but WITHOUT
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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 * version 2 for more details (a copy is included in the LICENSE file that
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 * accompanied this code).
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 *
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 * You should have received a copy of the GNU General Public License version
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 * 2 along with this work; if not, write to the Free Software Foundation,
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 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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 *
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 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 * or visit www.oracle.com if you need additional information or have any
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 * questions.
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 *
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 */
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#ifndef SHARE_VM_RUNTIME_TASK_HPP
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#define SHARE_VM_RUNTIME_TASK_HPP
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#include "memory/allocation.hpp"
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#include "runtime/timer.hpp"
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// A PeriodicTask has the sole purpose of executing its task
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// function with regular intervals.
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// Usage:
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//   PeriodicTask pf(10);
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//   pf.enroll();
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//   ...
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//   pf.disenroll();
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class PeriodicTask: public CHeapObj<mtInternal> {
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 public:
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  // Useful constants.
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  // The interval constants are used to ensure the declared interval
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  // is appropriate;  it must be between min_interval and max_interval,
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  // and have a granularity of interval_gran (all in millis).
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  enum { max_tasks     = 10,       // Max number of periodic tasks in system
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         interval_gran = 10,
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         min_interval  = 10,
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         max_interval  = 10000 };
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  static int num_tasks()   { return _num_tasks; }
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 private:
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  int _counter;
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  const int _interval;
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  static int _num_tasks;
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  static PeriodicTask* _tasks[PeriodicTask::max_tasks];
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  // Can only be called by the WatcherThread
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  static void real_time_tick(int delay_time);
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#ifndef PRODUCT
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  static elapsedTimer _timer;                      // measures time between ticks
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  static int _ticks;                               // total number of ticks
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  static int _intervalHistogram[max_interval];     // to check spacing of timer interrupts
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 public:
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  static void print_intervals();
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#endif
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  // Only the WatcherThread can cause us to execute PeriodicTasks
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  friend class WatcherThread;
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  PeriodicTask(size_t interval_time); // interval is in milliseconds of elapsed time
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  ~PeriodicTask();
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  // Make the task active
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  // For dynamic enrollment at the time T, the task will execute somewhere
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  // between T and T + interval_time.
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  void enroll();
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  // Make the task deactive
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  void disenroll();
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  void execute_if_pending(int delay_time) {
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    // make sure we don't overflow
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    jlong tmp = (jlong) _counter + (jlong) delay_time;
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    if (tmp >= (jlong) _interval) {
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      _counter = 0;
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      task();
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    } else {
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      _counter += delay_time;
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    }
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  }
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  // Returns how long (time in milliseconds) before the next time we should
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  // execute this task.
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  int time_to_next_interval() const {
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    assert(_interval > _counter,  "task counter greater than interval?");
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    return _interval - _counter;
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  }
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  // Calculate when the next periodic task will fire.
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  // Called by the WatcherThread's run method.
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  // Requires the PeriodicTask_lock.
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  static int time_to_wait();
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  // The task to perform at each period
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  virtual void task() = 0;
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};
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#endif // SHARE_VM_RUNTIME_TASK_HPP