QThread call-once semantics?

[danadam]

Well, it's about access serialization, so I would use QMutex:

// Singleton.h
#include <QMutex>
 
class Singleton
{
public:
    static Singleton *getInstance();
 
private:
    Singleton();
 
    static Singleton *instance;
    static QMutex instanceMutex;
};
 
// Singleton.cpp
#include <QtDebug>
#include <QMutexLocker>
 
Singleton *Singleton::instance(0);
QMutex Singleton::instanceMutex;
 
Singleton *Singleton::getInstance()
{
    if (!instance) {
        QMutexLocker instanceMutexLocker(&instanceMutex);
        if (!instance) {
            instance = new Singleton();
        }
    }
 
    return instance;
}
 
Singleton::Singleton()
{
    qDebug() << "Singleton ctor()";
}

// Singleton.h
#include <QMutex>

class Singleton
{
public:
    static Singleton *getInstance();

private:
    Singleton();

    static Singleton *instance;
    static QMutex instanceMutex;
};

// Singleton.cpp
#include <QtDebug>
#include <QMutexLocker>

Singleton *Singleton::instance(0);
QMutex Singleton::instanceMutex;

Singleton *Singleton::getInstance()
{
    if (!instance) {
        QMutexLocker instanceMutexLocker(&instanceMutex);
        if (!instance) {
            instance = new Singleton();
        }
    }

    return instance;
}

Singleton::Singleton()
{
    qDebug() << "Singleton ctor()";
}

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[brcain]

Well, it's about access serialization, so I would use QMutex

Yep. I knew I could do that for this case. Maybe call-once semantics is unnecessary with the mutex. I wonder why Boost thought it necessary ... other cases that it might address.

Do you know if Qt has something similar ... just as a mental note?

[danadam]

I wonder why Boost thought it necessary ... other cases that it might address.

Unfortunately I'm not very much familiar with boost, and I cannot think up any reason.

Do you know if Qt has something similar

I've never come across anything similar, but I've been dealing with Qt for only a few months, so it doesn't mean that no such thing exists.

[jacek]

Do you know if Qt has something similar ... just as a mental note?

You can construct it yourself using QMutex or QSemaphore.

[brcain]

You can construct it yourself using QMutex or QSemaphore.

Yep ... did that

Thanks