Introduction

Meziantou.Framework.SingleInstance provides the SingleInstance class: it tells an application whether it is the first running instance, and lets the next instances send their command-line arguments to the first one before they exit.

A typical use is a document editor: when the user opens a second file from the file explorer, the operating system starts a new process. That process notices that the editor is already running, sends the file name to it, and exits. The running editor opens the file in a new tab.

What you can do with it

• Detect the first instance with StartApplication, which returns true in the first process and false in the others. See Getting started.
• Send the arguments to the first instance with NotifyFirstInstance, and handle them in the NewInstance event. See Receiving notifications.
• Only detect a running instance, without listening for notifications. See Getting started.

Principles

• One instance per user. Two users of the same machine can each run their own instance. See How it works for the exact scope on each operating system.
• Cross-platform. It works on Windows, Linux and macOS. The notification uses a named pipe, which is backed by a Unix domain socket on Linux and macOS.
• Identified by a GUID. Every process of the application creates its SingleInstance with the same application id. Generate a new GUID once for your application and keep it in the code.

Namespace

The types are in the Meziantou.Framework namespace:

Next steps

• Getting started: install the package and make a console application single-instance.
• Receiving notifications: handle the arguments of the next instances.