requestSingleInstanceLock

The return value of this method indicates whether or not this instance of your application successfully obtained the lock. If it failed to obtain the lock, you can assume that another instance of your application is already running with the lock and exit immediately.

I.e. This method returns true if your process is the primary instance of your application and your app should continue loading. It returns false if your process should immediately quit as it has sent its parameters to another instance that has already acquired the lock.

On macOS, the system enforces single instance automatically when users try to open a second instance of your app in Finder, and the open-file and open-url events will be emitted for that. However when users start your app in command line, the system's single instance mechanism will be bypassed, and you have to use this method to ensure single instance.

An example of activating the window of primary instance when a second instance starts: