Qt:单实例应用程序保护的最佳实践

Question

QSingleApplication？QMutex？QSharedMemory？我正在寻找能在Windows,OSX和Linux(Ubuntu)中顺利运行的东西.使用Qt 4.7.1

Answer 1

简单的解决方案,做你想要的.没有网络依赖(as QtSingleApplication),没有任何开销.

用法:

int main()
{
    RunGuard guard( "some_random_key" );
    if ( !guard.tryToRun() )
        return 0;

    QAppplication a(/*...*/);
    // ...
}

RunGuard.h

#ifndef RUNGUARD_H
#define RUNGUARD_H

#include <QObject>
#include <QSharedMemory>
#include <QSystemSemaphore>


class RunGuard
{

public:
    RunGuard( const QString& key );
    ~RunGuard();

    bool isAnotherRunning();
    bool tryToRun();
    void release();

private:
    const QString key;
    const QString memLockKey;
    const QString sharedmemKey;

    QSharedMemory sharedMem;
    QSystemSemaphore memLock;

    Q_DISABLE_COPY( RunGuard )
};


#endif // RUNGUARD_H

RunGuard.cpp

#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();
}

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

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

    return isRunning;
}

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

Answer 2

由于QtSingleApplication相对过时且不再维护，因此我编写了一个替代文件，称为SingleApplication。

它基于QSharedMemory并使用QLocalServer来通知父进程正在生成的新实例。它适用于所有平台，并与Qt 5兼容。

完整的代码和文档可在此处获得。

Answer 3

您可以使用QSharedMemory特定的密钥并检查是否可以创建具有该密钥的共享内存。如果它也无法创建它，则实例已经运行：

QSharedMemory sharedMemory;
sharedMemory.setKey("MyApplicationKey");

if (!sharedMemory.create(1))
{
    QMessageBox::warning(this, tr("Warning!"), tr("An instance of this application is running!") );

    exit(0); // Exit already a process running
}