原本项目中使用QSharedMemory的方法来判断当前是否已存在运行的实例，但在MacOS上，当程序异常崩溃后，QSharedMemory没有被正常销毁，导致应用程序无法再次被打开。

        对此，Qt assistant中有相关说明：

        摘抄 qt-solutions/qtsingleapplication at master · qtproject/qt-solutions (github.com) 实现了一个single application的类，记录下来：

main.cpp

#include "mainwindow.h"
#include "singleapplication.h"int main(int argc, char *argv[])
{CSingleApplication a(argc, argv);if (a.isRunning()) {return 0;}MainWindow w;w.show();a.setActivationWindow(&w);return a.exec();
}

singleapplication.cpp

#include "singleapplication.h"
#include <QFileInfo>
#include <QLocalSocket>
#include <QLocalServer>
#include <QWidget>CSingleApplication::CSingleApplication(int& argc, char** argv): QApplication(argc, argv)
{m_strServerName = QFileInfo(QCoreApplication::applicationFilePath()).fileName();initLocalConn();
}CSingleApplication::~CSingleApplication()
{}bool CSingleApplication::isRunning()
{return m_isRunning;
}void CSingleApplication::setActivationWindow(QWidget* w)
{m_pActivateWin = w;
}void CSingleApplication::initLocalConn()
{m_isRunning = false;QLocalSocket socket;socket.connectToServer(m_strServerName);if (socket.waitForConnected(200)) {m_isRunning = true;return;}createLocalServer();
}void CSingleApplication::createLocalServer()
{m_pLocalServer = new QLocalServer(this);connect(m_pLocalServer, &QLocalServer::newConnection, this, &CSingleApplication::onNewConnection);if (!m_pLocalServer->listen(m_strServerName)) {if (QAbstractSocket::AddressInUseError == m_pLocalServer->serverError()) {QLocalServer::removeServer(m_strServerName);m_pLocalServer->listen(m_strServerName);}}
}void CSingleApplication::activateWindow()
{if (nullptr != m_pActivateWin) {m_pActivateWin->show();m_pActivateWin->raise();m_pActivateWin->activateWindow();}
}void CSingleApplication::onNewConnection()
{if (nullptr == m_pLocalServer) {return;}QLocalSocket* socket = m_pLocalServer->nextPendingConnection();if (nullptr != socket) {socket->waitForReadyRead(300);delete socket;activateWindow();}
}

singleapplication.h

#ifndef CSINGLEAPPLICATION_H
#define CSINGLEAPPLICATION_H#include <QApplication>class QLocalServer;class CSingleApplication : public QApplication
{
public:CSingleApplication(int& argc, char** argv);virtual ~CSingleApplication() override;public:bool isRunning();void setActivationWindow(QWidget* w);private:bool          m_isRunning = false;QWidget*      m_pActivateWin = nullptr;QString       m_strServerName;QLocalServer* m_pLocalServer = nullptr;void initLocalConn();void createLocalServer();void activateWindow();private slots:void onNewConnection();
};#endif // CSINGLEAPPLICATION_H