runguard.cpp

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/*
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
 * for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, see <http://www.gnu.org/licenses/>
 *
 * Additional note on redistribution: The copyright and license notices above
 * must be maintained in each individual source file that is a derivative work
 * of this source file; otherwise redistribution is prohibited.
 */

#include "runguard.h"

#include <QCryptographicHash>

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;
}
}

RunGuard::RunGuard(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();
}

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

RunGuard &RunGuard::instance(const QString &key)
{
    static RunGuard instance(key);
    return instance;
}

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

    memLock.acquire();
    const bool isRunning = sharedMem.attach();
    if (isRunning) {
        *static_cast<quint64 *>(sharedMem.data()) += 1;
        sharedMem.detach();
    }
    memLock.release();

    return isRunning;
}

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

    memLock.acquire();
    const bool result = sharedMem.create(sizeof(quint64));
    if (result)
        *static_cast<quint64 *>(sharedMem.data()) = 0;
    memLock.release();
    if (!result) {
        release();
        return false;
    }

    return true;
}

quint64 RunGuard::secondaryAttempts()
{
    quint64 ret = 0;
    memLock.acquire();
    if (!sharedMem.isAttached() && sharedMem.attach(QSharedMemory::ReadOnly)) {
        ret = *static_cast<quint64 *>(sharedMem.data());
        sharedMem.detach();
    } else {
        ret = *static_cast<quint64 *>(sharedMem.data());
    }
    memLock.release();
    return ret;
}

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