cetium · August 10, 2021 08:38 · Sep 11, 2016
diff --git a/AppRunGuard.cpp b/AppRunGuard.cpp
@@ -0,0 +1,78 @@
+//
+// Created by Andrey Streltsov on 11/06/15.
+// Based on code from here: http://stackoverflow.com/a/28172162/365754
+
+#include "AppRunGuard.h"
+#include <qcryptographichash.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;
+    }
+
+}
+
+
+AppRunGuard::AppRunGuard( const QString& key )
+        : key( key )
+        , memLockKey( generateKeyHash( key, "_memLockKey" ) )
+        , sharedmemKey( generateKeyHash( key, "_sharedmemKey" ) )
+        , sharedMem( sharedmemKey )
+        , memLock( memLockKey, 1 )
+{
+    QSharedMemory fix( sharedmemKey );    // Fix for *nix: http://habrahabr.ru/post/173281/
+    fix.attach();
+}
+
+AppRunGuard::~AppRunGuard()
+{
+    release();
+}
+
+bool AppRunGuard::isAnotherRunning()
+{
+    if ( sharedMem.isAttached() )
+        return false;
+
+    memLock.acquire();
+    const bool isRunning = sharedMem.attach();
+    if ( isRunning )
+        sharedMem.detach();
+    memLock.release();
+
+    return isRunning;
+}
+
+bool AppRunGuard::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 AppRunGuard::release()
+{
+    memLock.acquire();
+    if ( sharedMem.isAttached() )
+        sharedMem.detach();
+    memLock.release();
+}
diff --git a/AppRunGuard.h b/AppRunGuard.h
@@ -0,0 +1,34 @@
+//
+// Created by Andrey Streltsov on 11/06/15.
+// Based on code from here: http://stackoverflow.com/a/28172162/365754
+
+#ifndef RUNGUARD_H
+#define RUNGUARD_H
+#include <QString>
+#include <qsharedmemory.h>
+#include <qsystemsemaphore.h>
+
+
+class AppRunGuard : public QObject {
+
+public:
+    AppRunGuard( const QString& key );
+    virtual ~AppRunGuard();
+
+    bool isAnotherRunning();
+    bool tryToRun();
+    void release();
+
+private:
+    const QString key;
+    const QString memLockKey;
+    const QString sharedmemKey;
+
+    QSharedMemory sharedMem;
+    QSystemSemaphore memLock;
+
+    Q_DISABLE_COPY(AppRunGuard)
+};
+
+
+#endif // RUNGUARD_H
diff --git a/main.cpp b/main.cpp
@@ -0,0 +1,16 @@
+//
+// Created by Andrey Streltsov on 11/06/15.
+// Usage example
+
+#define kAppRunUUID "your-app-instance-uuid-here"
+
+int main(int argc, char *argv[]) {
+
+	AppRunGuard guard(kAppRunUUID);
+    if ( !guard.tryToRun() )
+        return 1;
+
+  QApplication app(argc, argv);
+    return app.exec();
+
+}
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