qtconcurrentiteratekernel.cpp

Go to the documentation of this file.

/****************************************************************************
**
** Copyright (C) 2014 Digia Plc and/or its subsidiary(-ies).
** Contact: http://www.qt-project.org/legal
**
** This file is part of the QtCore module of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and Digia.  For licensing terms and
** conditions see http://qt.digia.com/licensing.  For further information
** use the contact form at http://qt.digia.com/contact-us.
**
** GNU Lesser General Public License Usage
** Alternatively, this file may be used under the terms of the GNU Lesser
** General Public License version 2.1 as published by the Free Software
** Foundation and appearing in the file LICENSE.LGPL included in the
** packaging of this file.  Please review the following information to
** ensure the GNU Lesser General Public License version 2.1 requirements
** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
**
** In addition, as a special exception, Digia gives you certain additional
** rights.  These rights are described in the Digia Qt LGPL Exception
** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
**
** GNU General Public License Usage
** Alternatively, this file may be used under the terms of the GNU
** General Public License version 3.0 as published by the Free Software
** Foundation and appearing in the file LICENSE.GPL included in the
** packaging of this file.  Please review the following information to
** ensure the GNU General Public License version 3.0 requirements will be
** met: http://www.gnu.org/copyleft/gpl.html.
**
**
** $QT_END_LICENSE$
**
****************************************************************************/

#include "qtconcurrentiteratekernel.h"

#if defined(Q_OS_MAC)
#include <mach/mach.h>
#include <mach/mach_time.h>
#include <unistd.h>
#elif defined(Q_OS_UNIX)
#if defined(Q_OS_HURD)
#include <sys/time.h>
#endif
#include <time.h>
#include <unistd.h>
#elif defined(Q_OS_WIN)
#include <qt_windows.h>
#endif

#include "private/qfunctions_p.h"


#ifndef QT_NO_CONCURRENT

QT_BEGIN_NAMESPACE

enum {
    TargetRatio = 100,
    MedianSize = 7
};

#if defined(Q_OS_MAC)

static qint64 getticks()
{
    return mach_absolute_time();
}

#elif defined(Q_OS_UNIX)


static qint64 getticks()
{
#if defined(_POSIX_TIMERS) && (_POSIX_TIMERS > 0)
    clockid_t clockId;

#ifndef _POSIX_THREAD_CPUTIME
    clockId = CLOCK_REALTIME;
#elif (_POSIX_THREAD_CPUTIME-0 <= 0)
    // if we don't have CLOCK_THREAD_CPUTIME_ID, we have to just use elapsed realtime instead
    clockId = CLOCK_REALTIME;

#  if (_POSIX_THREAD_CPUTIME-0 == 0)
    // detect availablility of CLOCK_THREAD_CPUTIME_ID
    static long useThreadCpuTime = -2;
    if (useThreadCpuTime == -2) {
        // sysconf() will return either -1 or _POSIX_VERSION (don't care about thread races here)
        useThreadCpuTime = sysconf(_SC_THREAD_CPUTIME);
    }
    if (useThreadCpuTime != -1)
        clockId = CLOCK_THREAD_CPUTIME_ID;
#  endif
#else
    clockId = CLOCK_THREAD_CPUTIME_ID;
#endif

    struct timespec ts;
    if (clock_gettime(clockId, &ts) == -1)
        return 0;
    return (ts.tv_sec * 1000000000) + ts.tv_nsec;
#else

#ifdef Q_OS_SYMBIAN
    return clock();
#else
    // no clock_gettime(), fall back to wall time
    struct timeval tv;
    gettimeofday(&tv, 0);
    return (tv.tv_sec * 1000000) + tv.tv_usec;
#endif

#endif
}

#elif defined(Q_OS_WIN)

static qint64 getticks()
{
    LARGE_INTEGER x;
    if (!QueryPerformanceCounter(&x))
        return 0;
    return x.QuadPart;
}

#endif

static double elapsed(qint64 after, qint64 before)
{
    return double(after - before);
}

namespace QtConcurrent {

BlockSizeManager::BlockSizeManager(int iterationCount)
: maxBlockSize(iterationCount / (QThreadPool::globalInstance()->maxThreadCount() * 2)),
  beforeUser(0), afterUser(0),
  controlPartElapsed(MedianSize), userPartElapsed(MedianSize),
  m_blockSize(1)
{ }

// Records the time before user code.
void BlockSizeManager::timeBeforeUser()
{
    if (blockSizeMaxed())
        return;

    beforeUser = getticks();
    controlPartElapsed.addValue(elapsed(beforeUser, afterUser));
}

 // Records the time after user code and adjust the block size if we are spending
 // to much time in the for control code compared with the user code.
void BlockSizeManager::timeAfterUser()
{
    if (blockSizeMaxed())
        return;

    afterUser = getticks();
    userPartElapsed.addValue(elapsed(afterUser, beforeUser));

    if (controlPartElapsed.isMedianValid() == false)
        return;

    if (controlPartElapsed.median() * TargetRatio < userPartElapsed.median())
        return;

    m_blockSize = qMin(m_blockSize * 2,  maxBlockSize);

#ifdef QTCONCURRENT_FOR_DEBUG
    qDebug() << QThread::currentThread() << "adjusting block size" << controlPartElapsed.median() << userPartElapsed.median() << m_blockSize;
#endif

    // Reset the medians after adjusting the block size so we get
    // new measurements with the new block size.
    controlPartElapsed.reset();
    userPartElapsed.reset();
}

int BlockSizeManager::blockSize()
{
    return m_blockSize;
}

} // namespace QtConcurrent

QT_END_NAMESPACE

#endif // QT_NO_CONCURRENT