Single Instance

Work in Progress

This guide is under development. Check back soon!

Overview

Hermes provides single-instance support to ensure only one copy of your application runs at a time. When a second instance launches, its command-line arguments are forwarded to the first instance via named pipes, then the second instance exits.

Quick Reference

With Blazor

var builder = HermesBlazorAppBuilder.CreateDefault(args);

builder.SingleInstance("com.mycompany.myapp", guard =>
{
    guard.SecondInstanceLaunched += newArgs =>
    {
        // Use window.Invoke() to marshal to the UI thread if needed
        Console.WriteLine($"Second instance launched with {newArgs.Length} arg(s)");
    };
});

builder.ConfigureWindow(options =>
{
    options.Title = "My App";
});

var app = builder.Build();
app.Run();

The Blazor extension handles second-instance detection automatically: if another instance is already running, it forwards the current args and exits. The SingleInstanceGuard is registered as a singleton in DI.

Without Blazor

using var guard = HermesApplication.SingleInstance("com.mycompany.myapp");

if (!guard.IsFirstInstance)
{
    guard.NotifyFirstInstance(args);
    return;
}

guard.SecondInstanceLaunched += newArgs =>
{
    Console.WriteLine($"Received args: {string.Join(", ", newArgs)}");
};

var window = new HermesWindow()
    .SetTitle("My App")
    .SetSize(1024, 768);

window.WaitForClose();

Application ID

The application ID must contain only alphanumeric characters, hyphens, underscores, and dots. Use a reverse-domain style identifier:

• com.mycompany.myapp
• my-app-name

Key Types

Type	Description
SingleInstanceGuard	Manages the mutex and named pipe listener
IsFirstInstance	true if this is the primary instance
SecondInstanceLaunched	Event fired when another instance sends args
NotifyFirstInstance(args)	Sends args to the primary instance

Coming Soon

• Bring-to-front behavior on second launch
• Integration with window focus