JKQtPlotter/lib/jkqtplottertools/jkqtphighrestimer.h

/*
    Copyright (c) 2008-2015 Jan W. Krieger (<jan@jkrieger.de>, <j.krieger@dkfz.de>) (DKFZ) & IWR, University of Heidelberg

    last modification: $LastChangedDate: 2015-06-10 19:19:10 +0200 (Mi, 10 Jun 2015) $  (revision $Rev: 3976 $)

    This software is free software: you can redistribute it and/or modify
    it under the terms of the GNU Lesser General Public License (LGPL) as published by
    the Free Software Foundation, either version 2 of the License, or
    (at your option) any later version.

    This program 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 Lesser General Public License (LGPL) for more details.

    You should have received a copy of the GNU Lesser General Public License (LGPL)
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/


/**
 * \defgroup highrestimer_group High Resolution Timer
 * \ingroup tools
 *
 * This group contains a class that implements a high-resolution timer. Note that this
 * is highly system-dependent and you will find a way to implement this on your OS!
 */
/*@{*/

/** \file highrestimer.h
 *  \ingroup highrestimer_group
 */

#include <cmath>
#include <cstdlib>
#include <iostream>

#ifndef __WINDOWS__
# if defined(WIN32) || defined(WIN64) || defined(_MSC_VER) || defined(_WIN32)
#  define __WINDOWS__
# endif
#endif

#ifndef __LINUX__
# if defined(linux)
#  define __LINUX__
# endif
#endif

#ifndef __WINDOWS__
# ifndef __LINUX__
#  warning("these methods are ment to be used under windows or linux ... no other system were tested")
# endif
#endif

#if defined(__WINDOWS__)
  #include<windows.h>
#elif defined(__LINUX__)
  #include <sys/time.h>
#else
  #warning("your operating system is not supported: you will have to implement this on your systems")
  #include <sys/time.h>
#endif



#ifndef JKQTPHIGHRESTIMER_H
#define JKQTPHIGHRESTIMER_H


/**
 * \brief This class implements a high resolution timer capable of measuring time intervals with a resolution
 *        of some microseconds
 * \ingroup highrestimer_group
 *
 * \attention Note that this is a MS Windows specific implementation od a high-resolution timer using some of
 * windows' API methods (namely \c QueryPerformanceCounter() and \c QueryPerformanceFrequency() ). So if you want
 * to use this class on non-win32 systems you will have to find a way to implement it for your system!!!
 *
 * \attention Also note that a standard windows system is NOT a real time OS. So do not expect to get a high accuracy
 * when timing operations using this timer. It gives you an accurate time stamp, but it can not guarantee when
 * the code is executed!
 *
 *
 * The timer works very simple:
 *   - you can start the timer with start() which means you set a time=0
 *   - then you can query the time difference to the last call of start() by using get_time().
 * .
 *
 * There is also a test method test() which will try to give you a feel for the performance of the timer in
 * a simple application on your computer.
 * It simply does some thousand iterations and records the time needed for each single iteration. Then it may
 * calculate a histogram, a mean value and a standard deviation from these times.
 *
 * This is the result of test() on a WinXP system, Athlon64 X2 3800+ (2GHz):
 * \image html highrestimer.png
 * Note that this histogram tells you more about how your system works than about the timer itself.
 * What we can find out about the timer is that it really provides a resolution in the microsecond region. This can
 * be seen, as there is a non-zero minimal measured interval (1.67619 usec). This basically tells us the run-time of
 * the measurement loop. There are also bigger run-times which are produced, as this program ran on a multi-process
 * (not process<b>or</b> !!!) OS, which means that the current process may be stalled to allow othe rprocesses to
 * execute. If this would run on a single-process system we should only get one run-time, if we assume that all
 * methods need a fixed amount of time. So we can use this method to test whether our system provides a sufficiently
 * accurate time. The 1.68 usec give an upper bound for the timer interval and thus the resolution they do <b>not</b>
 * represent the timer resolution. To get this nominal resolution in a windows system you could use the WinAPI method
 * \c QueryPerformanceFrequency() which is used in the method get_time(). On my system the timer frequency is 3.57955 MHz
 * which corresponds to a resolution of 0.2794 usec.
 *
 * \par win32 implementation issues:
 * To implement this timer on windows systems I use two API calls from the windows kernel. They are:
 *   - <a href="http://msdn2.microsoft.com/en-us/library/ms644904.aspx">QueryPerformanceCounter()</a>
 *   - <a href="http://msdn2.microsoft.com/en-us/library/ms644905.aspx">QueryPerformanceFrequency()</a>
 * .
 * \n
 * The first one is used to read times: In the start() method we simply save the current counter value to a variable.
 * In get_time() we can then again use QueryPerformanceCounter() to get the current counter value and then calculate
 * the difference between these two. Using QueryPerformanceFrequency() we can calculate the time difference in usecs
 * from the counter value difference using:
 *   \f[ \Delta t=\frac{N_{\mbox{now}}-N_{\mbox{start}}}{\mbox{\texttt{QueryPerformanceFrequency()}}}\cdot 10^{6} \f]
 *
 * \par why not standard POSIX?
 * The standard POSIX time functions available in a MinGW environment have a resolution that is in the range of
 * some 10 milliseconds. This may be enough for many purposes, but for exact time measurement, as you will want
 * to do it on measurement and control systems this is not sufficient. So I tried to find a possibility to
 * implement a system-independent high-resolution timer. As most timer stuff depends on very low-level kernel
 * calls on every operating system this seems to be nearly impossible. So I implemented this timer for win32 only,
 * as this is the system we use in the lab.
 *
 * \par linux implementation possibility:
 * This class does not implement a timer for Linux/Unix systems but I
 * will provide you with a small hint how you could implement one here:
 * The <a href="http://www.gnu.org/software/libc/manual/html_node/High_002dResolution-Calendar.html">\c gettimeofday()
 * method</a> from the libc seems to have enough tim resolution for our pourposes, so try to use this for the high-
 * resolution timer. As mentioned above this method is not available for MinGW in win32 which is the main development
 * platform for this project.
 *
 * \test you can find an example application in the file \link test_hrestimer.cpp .
 *
 */
class JKQTPHighResTimer {
  protected:
    #ifdef __WINDOWS__
      /** \brief internal: time stamp of the last call of start() */
      LARGE_INTEGER last;

      /** \brief internal: timer frequency */
      double freq;
    #else
      struct timeval last;
    #endif
	public:
		/** \brief class constructor. */
        JKQTPHighResTimer();
		/** \brief class destructor */
        ~JKQTPHighResTimer();
		/** \brief start the timer */
		void start();
		/** \brief get the time since the last call of start() in microseconds */
		double get_time();
		/** \brief test the resolution
     *
     * mean value and standard deviation of 1000000 timer polls will be evaluated and returned in \c mean
     * and \c stddev. If you supply \c histogram with a pointer to a memory array with \c histogram_size
     * items this will hold afterwards a histogram of the data. \c histogram_x wil contain the time interval
     * values of the histogram bins in \c histogram.
     *
     * To measure the resolution this method uses this code:
     * \code
double l=get_time(), n;
for (unsigned long i=0; i<runs; i++) {
  n=get_time();
  h[i]=n-l;
  l=n;
}
\endcode
     *
     */
		void test(double* mean, double* stddev, unsigned long* histogram=nullptr, double* histogram_x=nullptr, unsigned long histogram_size=0);

};





#endif // JKQTPHIGHRESTIMER_H

/*@}*/