qt-creator/tests/benchmarks/signals/tst_bench_signals.cpp

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#include <QtTest>

#include <functional>
#include <vector>


/*
Config: Using QtTest library 5.10.0, Qt 5.10.0 (x86_64-little_endian-lp64 shared (dynamic)
    debug build; by GCC 7.2.1 20171205)

PASS   : BenchmarkSignals::qtMemfun()
     0.000068 msecs per iteration (total: 72, iterations: 1048576)
PASS   : BenchmarkSignals::qtLambda()
     0.000066 msecs per iteration (total: 70, iterations: 1048576)
PASS   : BenchmarkSignals::manualBind()
     0.00011 msecs per iteration (total: 60, iterations: 524288)
PASS   : BenchmarkSignals::manualLambda()
     0.000043 msecs per iteration (total: 91, iterations: 2097152)


CONFIG += release

********* Start testing of BenchmarkSignals *********
PASS   : BenchmarkSignals::qtMemfun()
     0.000061 msecs per iteration (total: 64, iterations: 1048576)
PASS   : BenchmarkSignals::qtLambda()
     0.000058 msecs per iteration (total: 61, iterations: 1048576)

 // Not completely surprising, as all the top call can be inlined

PASS   : BenchmarkSignals::manualBind()
     0.0000078 msecs per iteration (total: 66, iterations: 8388608)
PASS   : BenchmarkSignals::manualLambda()
     0.00000596 msecs per iteration (total: 100, iterations: 16777216)
PASS   : BenchmarkSignals::cleanupTestCase()


The latter in instructions:

PASS   : BenchmarkSignals::qtMemfun()
     445 instruction reads per iteration (total: 445, iterations: 1)
PASS   : BenchmarkSignals::qtLambda()
     440 instruction reads per iteration (total: 440, iterations: 1)
PASS   : BenchmarkSignals::manualBind()
     113 instruction reads per iteration (total: 113, iterations: 1)
PASS   : BenchmarkSignals::manualLambda()
     107 instruction reads per iteration (total: 107, iterations: 1)

*/


template <typename Type>
class NaiveSignal
{
public:
    using Callable = std::function<Type>;

    void connect(const Callable &callable) { m_callables.push_back(callable); }

    template <typename ...Args>
    void operator()(Args ...args) const
    {
        for (const Callable &callable : m_callables)
            callable(args...);
   }

private:
    std::vector<Callable> m_callables;
};


class BenchmarkSignals : public QObject
{
    Q_OBJECT

public:
    BenchmarkSignals() {}

private slots:
    void qtMemfun();
    void qtLambda();
    void manualBind();
    void manualLambda();
};

class Tester : public QObject
{
    Q_OBJECT

public:
    NaiveSignal<void(int)> naiveSignal;

signals:
    void qtSignal(int);

public:
    void doit(int i) { sum += i; }
    int sum = 0;
};

void BenchmarkSignals::qtMemfun()
{
    Tester tester;
    connect(&tester, &Tester::qtSignal, &tester, &Tester::doit);
    QBENCHMARK {
        tester.qtSignal(1);
    }
}

void BenchmarkSignals::qtLambda()
{
    Tester tester;
    connect(&tester, &Tester::qtSignal, [&](int x) { tester.sum += x; });
    QBENCHMARK {
        tester.qtSignal(1);
    }
}

void BenchmarkSignals::manualBind()
{
    Tester tester;
    tester.naiveSignal.connect(std::bind(&Tester::doit, &tester, std::placeholders::_1));
    QBENCHMARK {
        tester.naiveSignal(1);
    }
}

void BenchmarkSignals::manualLambda()
{
    Tester tester;
    tester.naiveSignal.connect([&](int x) { tester.sum += x; });
    QBENCHMARK {
        tester.naiveSignal(1);
    }
}

QTEST_MAIN(BenchmarkSignals)

#include "tst_bench_signals.moc"