/*

 * Copyright 2001-2007 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.

 *

 */

// COTracker keeps track of the concurrent overhead of a GC thread.

// A thread that needs to be tracked must, itself, start up its

// tracker with the start() method and then call the update() method

// at regular intervals. What the tracker does is to calculate the

// concurrent overhead of a process at a given update period. The

// tracker starts and when is detects that it has exceeded the given

// period, it calculates the duration of the period in wall-clock time

// and the duration of the period in vtime (i.e. how much time the

// concurrent processes really took up during this period). The ratio

// of the latter over the former is the concurrent overhead of that

// process for that period over a single CPU. This overhead is stored

// on the tracker, "timestamped" with the wall-clock time of the end

// of the period. When the concurrent overhead of this process needs

// to be queried, this last "reading" provides a good approximation

// (we assume that the concurrent overhead of a particular thread

// stays largely constant over time). The timestamp is necessary to

// detect when the process has stopped working and the recorded

// reading hasn't been updated for some time.

// Each concurrent GC thread is considered to be part of a "group"

// (i.e. any available concurrent marking threads are part of the

// "concurrent marking thread group"). A COTracker is associated with

// a single group at construction-time. It's up to each collector to

// decide how groups will be mapped to such an id (ids should start

// from 0 and be consecutive; there's a hardcoded max group num

// defined on the GCOverheadTracker class). The notion of a group has

// been introduced to be able to identify how much overhead was

// imposed by each group, instead of getting a single value that

// covers all concurrent overhead.

class COTracker {

private:

  // It indicates whether this tracker is enabled or not. When the

  // tracker is disabled, then it returns 0.0 as the latest concurrent

  // overhead and several methods (reset, start, and update) are not

  // supposed to be called on it. This enabling / disabling facility

  // is really provided to make a bit more explicit in the code when a

  // particulary tracker of a processes that doesn't run all the time

  // (e.g. concurrent marking) is supposed to be used and not it's not.

  bool               _enabled;

  // The ID of the group associated with this tracker.

  int                _group;

  // The update period of the tracker. A new value for the concurrent

  // overhead of the associated process will be made at intervals no

  // smaller than this.

  double             _update_period_sec;

  // The start times (both wall-block time and vtime) of the current

  // interval.

  double             _period_start_time_sec;

  double             _period_start_vtime_sec;

  // Number seq of the concurrent overhead readings within a period

  NumberSeq          _conc_overhead_seq;

  // The latest reading of the concurrent overhead (over a single CPU)

  // imposed by the associated concurrent thread, made available at

  // the indicated wall-clock time.

  double             _conc_overhead;

  double             _time_stamp_sec;

  // The number of CPUs that the host machine has (for convenience

  // really, as we'd have to keep translating it into a double)

  static double      _cpu_number;

  // Fields that keep a list of all trackers created. This is useful,

  // since it allows us to sum up the concurrent overhead without

  // having to write code for a specific collector to broadcast a

  // request to all its concurrent processes.

  COTracker*         _next;

  static COTracker*  _head;

  // It indicates that a new period is starting by updating the

  // _period_start_time_sec and _period_start_vtime_sec fields.

  void resetPeriod(double now_sec, double vnow_sec);

  // It updates the latest concurrent overhead reading, taken at a

  // given wall-clock time.

  void setConcOverhead(double time_stamp_sec, double conc_overhead);

  // It determines whether the time stamp of the latest concurrent

  // overhead reading is out of date or not.

  bool outOfDate(double now_sec) {

    // The latest reading is considered out of date, if it was taken

    // 1.2x the update period.

    return (now_sec - _time_stamp_sec) > 1.2 * _update_period_sec;

  }

public:

  // The constructor which associates the tracker with a group ID.

  COTracker(int group);

  // Methods to enable / disable the tracker and query whether it is enabled.

  void enable()  { _enabled = true;  }

  void disable() { _enabled = false; }

  bool enabled() { return _enabled;  }

  // It resets the tracker and sets concurrent overhead reading to be

  // the given parameter and the associated time stamp to be now.

  void reset(double starting_conc_overhead = 0.0);

  // The tracker starts tracking. IT should only be called from the

  // concurrent thread that is tracked by this tracker.

  void start();

  // It updates the tracker and, if the current period is longer than

  // the update period, the concurrent overhead reading will be

  // updated. force_end being true indicates that it's the last call

  // to update() by this process before the tracker is disabled (the

  // tracker can be re-enabled later if necessary).  It should only be

  // called from the concurrent thread that is tracked by this tracker

  // and while the thread has joined the STS.

  void update(bool force_end = false);

  // It adjusts the contents of the tracker to take into account a STW

  // pause.

  void updateForSTW(double start_sec, double end_sec);

  // It returns the last concurrent overhead reading over a single

  // CPU. If the reading is out of date, or the tracker is disabled,

  // it returns 0.0.

  double concCPUOverhead(double now_sec) {

    if (!_enabled || outOfDate(now_sec))

      return 0.0;

    else

      return _conc_overhead;

  }

  // It returns the last concurrent overhead reading over all CPUs

  // that the host machine has. If the reading is out of date, or the

  // tracker is disabled, it returns 0.0.

  double concOverhead(double now_sec) {

    return concCPUOverhead(now_sec) / _cpu_number;

  }

  double predConcOverhead();

  void resetPred();

  // statics

  // It notifies all trackers about a STW pause.

  static void updateAllForSTW(double start_sec, double end_sec);

  // It returns the sum of the concurrent overhead readings of all

  // available (and enabled) trackers for the given time stamp. The

  // overhead is over all the CPUs of the host machine.

  static double totalConcOverhead(double now_sec);

  // Like the previous method, but it also sums up the overheads per

  // group number. The length of the co_per_group array must be at

  // least as large group_num

  static double totalConcOverhead(double now_sec,

                                  size_t group_num,

                                  double* co_per_group);

  static double totalPredConcOverhead();

};