qtconcurrentiteratekernel.cpp

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// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
 
#include "qtconcurrentiteratekernel.h"
 
#include <qdeadlinetimer.h>
#include "private/qfunctions_p.h"
 
 
#if !defined(QT_NO_CONCURRENT) || defined(Q_QDOC)
 
QT_BEGIN_NAMESPACE
 
enum {
    TargetRatio = 100
};
 
static qint64 getticks()
{
    return QDeadlineTimer::current(Qt::PreciseTimer).deadlineNSecs();
}
 
static double elapsed(qint64 after, qint64 before)
{
    return double(after - before);
}
 
namespace QtConcurrent {
 
BlockSizeManager::BlockSizeManager(QThreadPool *pool, int iterationCount)
    : maxBlockSize(iterationCount / (std::max(pool->maxThreadCount(), 1) * 2)),
      beforeUser(0), afterUser(0),
      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() * int(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