qbattsingle.cpp

/*
 * Solution suggested by Dmitry Sazonov
 * (http://stackoverflow.com/users/1035613/dmitry-sazonov)
 * - http://stackoverflow.com/a/28172162
 */

#include <QCryptographicHash>
#include "qbattsingle.h"

namespace
{
QString generateKeyHash(const QString& key, const QString& salt)
{
    QByteArray data;

    data.append(key.toUtf8());
    data.append(salt.toUtf8());
    data = QCryptographicHash::hash(data, QCryptographicHash::Sha1).toHex();

    return data;
}
}

QBattSingle::QBattSingle(const QString& key)
    : key(key)
    , memLockKey(generateKeyHash(key, "_memLockKey"))
    , sharedmemKey(generateKeyHash(key, "_sharedmemKey"))
    , sharedMem(sharedmemKey)
    , memLock(memLockKey, 1)
{
    memLock.acquire();
    {
        QSharedMemory fix(sharedmemKey);    // Fix for *nix: http://habrahabr.ru/post/173281/
        fix.attach();
    }
    memLock.release();
}

QBattSingle::~QBattSingle()
{
    release();
}

bool QBattSingle::isAnotherRunning()
{
    if (sharedMem.isAttached())
        return false;

    memLock.acquire();
    const bool isRunning = sharedMem.attach();
    if (isRunning)
        sharedMem.detach();
    memLock.release();

    return isRunning;
}

bool QBattSingle::tryToRun()
{
    if (isAnotherRunning())   // Extra check
        return false;

    memLock.acquire();
    const bool result = sharedMem.create(sizeof(quint64));
    memLock.release();
    if (!result) {
        release();
        return false;
    }

    return true;
}

void QBattSingle::release()
{
    memLock.acquire();
    if (sharedMem.isAttached())
        sharedMem.detach();
    memLock.release();
}