Meziantou.FrameworkHow it works
editDetecting the first instance
StartApplication tries to acquire a named mutex derived from the application id, without waiting. The process that owns the mutex is the first instance; the others get false. When the first instance exits, the operating system releases the mutex, and the next process that calls StartApplication becomes the first instance. A mutex left abandoned by a process that crashed is acquired as well.
Calling StartApplication again after it returned true returns true and does nothing else. Calling it after Dispose throws an ObjectDisposedException.
Scope of an instance
| Operating system | Scope |
|---|---|
| Windows | The logon session of the user: the mutex and the pipe are created in the Local\ namespace, and the pipe name includes the session id |
| Linux, macOS | The user: the names include a hash of the user name, so other users of the machine get their own instance |
On every operating system, the pipe only accepts connections from processes of the same user.
Notifications
When StartServer is true (the default), the first instance listens on a named pipe derived from the application id. On Linux and macOS, .NET implements named pipes with Unix domain sockets, whose file lives in the temporary folder.
NotifyFirstInstance connects to the pipe, sends the process id and the arguments in one message, and closes the connection. The first instance raises NewInstance for each message. A message that is truncated or malformed is ignored, and the first instance keeps accepting the next notifications.
Lifetime
SingleInstance implements IDisposable. Dispose stops the notification server and closes the mutex, so keep the object alive for as long as the application runs: store it in a field of the application, or declare it with using var at the top of Main, as in Getting started.