I'm working on a project that uses a QThread to process communication over a
TCP connection. In trying to improve performance I've tracked down an odd
slow-down when we use QMethod::invoke to force a method to be called on the
correct thread.
This is an embedded project running on a Freescale i.MX53. On this board, I've
measured the time to make this call and it is on average around 400000 ns. I've
measured this on our i.MX6 board as well (with only one core enabled) and it
takes only 60000 ns. This doesn't look right to me. I would expect the
difference to be at most 2x, not 6x.
Is there something I'm missing here in my expectations or is there something
fundamentally wrong causing this slow-down?
I'm including my test code which I've run on both targets. In the sample code
I'm using Qt::BlockingQueuedConnection when calling invoke - normally we don't
do that but for the test it makes it much simpler to see the effect of the
slow-down.
- Robert Daniels
#include <QCoreApplication>
#include <QThread>
#include <QMetaMethod>
#include <QDebug>
#include <QTimer>
#include <QElapsedTimer>
class WorkerThread : public QThread
{
Q_OBJECT
public:
WorkerThread()
{
moveToThread(this);
method =
metaObject()->method(metaObject()->indexOfMethod("myMethod(int)"));
start();
sum = 0;
qDebug() << "Started Worker Thread.";
}
Q_INVOKABLE void myMethod(int test)
{
if (currentThread() != this) {
method.invoke(this, Qt::BlockingQueuedConnection, Q_ARG(int, test));
} else {
sum += test;
}
}
int getSum() { return sum; }
private:
QMetaMethod method;
int sum;
};
class Test : public QObject
{
Q_OBJECT
public:
Test()
{
QTimer *timer = new QTimer(this);
timer->setInterval(10);
connect(timer, SIGNAL(timeout()), SLOT(onTimer()));
timer->start();
}
private slots:
void onTimer()
{
qDebug() << "Begin test.";
QElapsedTimer timer;
qint64 total = 0;
const int cnt = 100000;
for (int i = 0; i < cnt; i++) {
timer.start();
worker.myMethod(i);
total += timer.nsecsElapsed();
}
qDebug() << "Average ms:" << (total / cnt) << "sum =" <<
worker.getSum();
worker.exit();
QCoreApplication::exit();
}
private:
WorkerThread worker;
};
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
Test test;
return a.exec();
}
#include "main.moc"
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