QtSingleApplication: Replaced QtLockedFile with QLockFile (#4170)

This also drops support for Qt 4 in this part of the code, since
QLockFile was introduced in Qt 5.1. But it was already requiring Qt 5.4
due to use of qUtf8Printable anyway.

The same change was done for Qt Creator here:
https://codereview.qt-project.org/c/qt-creator/qt-creator/+/499187

src/qtsingleapplication/src/qtlocalpeer.cpp

@@ -42,8 +42,9 @@
 #include "qtlocalpeer.h"
 #include <QCoreApplication>
 #include <QDataStream>
+#include <QDir>
+#include <QLocalSocket>
 #include <QRegularExpression>
-#include <QTime>
 
 #if defined(Q_OS_WIN)
 #include <QLibrary>
@@ -64,15 +65,6 @@ static PProcessIdToSessionId pProcessIdToSessionId = 0;
 #include <unistd.h>
 #endif
 
-namespace QtLP_Private {
-#include "qtlockedfile.cpp"
-#if defined(Q_OS_WIN)
-#include "qtlockedfile_win.cpp"
-#else
-#include "qtlockedfile_unix.cpp"
-#endif
-}
-
 const char* QtLocalPeer::ack = "ack";
 
 QtLocalPeer::QtLocalPeer(QObject* parent, const QString &appId)
@@ -116,22 +108,19 @@ QtLocalPeer::QtLocalPeer(QObject* parent, const QString &appId)
     QString lockName = QDir(QDir::tempPath()).absolutePath()
                        + QLatin1Char('/') + socketName
                        + QLatin1String("-lockfile");
-    lockFile.setFileName(lockName);
-    lockFile.open(QIODevice::ReadWrite);
+    lockFile.reset(new QLockFile(lockName));
 }
 
-
-
 bool QtLocalPeer::isClient()
 {
-    if (lockFile.isLocked())
+    if (lockFile->isLocked())
         return false;
 
-    if (!lockFile.lock(QtLP_Private::QtLockedFile::WriteLock, false))
+    if (!lockFile->tryLock())
         return true;
 
     bool res = server->listen(socketName);
-#if defined(Q_OS_UNIX) && (QT_VERSION >= QT_VERSION_CHECK(4,5,0))
+#if defined(Q_OS_UNIX)
     // ### Workaround
     if (!res && server->serverError() == QAbstractSocket::AddressInUseError) {
         QFile::remove(QDir::cleanPath(QDir::tempPath())+QLatin1Char('/')+socketName);

src/qtsingleapplication/src/qtlocalpeer.h

@@ -42,10 +42,8 @@
 #define QTLOCALPEER_H
 
 #include <QLocalServer>
-#include <QLocalSocket>
-#include <QDir>
-
-#include "qtlockedfile.h"
+#include <QLockFile>
+#include <QScopedPointer>
 
 class QtLocalPeer : public QObject
 {
@@ -55,8 +53,7 @@ class QtLocalPeer : public QObject
     QtLocalPeer(QObject *parent = 0, const QString &appId = QString());
     bool isClient();
     bool sendMessage(const QString &message, int timeout);
-    QString applicationId() const
-        { return id; }
+    QString applicationId() const { return id; }
 
 Q_SIGNALS:
     void messageReceived(const QString &message);
@@ -68,7 +65,7 @@ protected Q_SLOTS:
     QString id;
     QString socketName;
     QLocalServer* server;
-    QtLP_Private::QtLockedFile lockFile;
+    QScopedPointer<QLockFile> lockFile;
 
 private:
     static const char* ack;