Daemon Services

In SanteDB, a daemon service represents a service which is activated on startup and is shut down on service stop. Daemon services can exist on the iCDR and dCDR interfaces. Daemon services are implemented using the IDaemonService

Daemons are particularly useful when:

• The plugin needs to subscribe to events on other services

• The plugin needs to register / configure other services on application start

• The plugin wants a long-running background task (like a messaging interface, listener, etc.)

Lifecycle

Daemons go through the same lifecycle as the primary application host. Daemons have their .Start() method called at Stage 2 of the application startup and their .Stop() method called when the application host is shutting down.

Implementation

Daemon Scaffolding

Implementing the IDaemonService interface is all that is required to indicate a particular implementation is a daemon.

public class HelloDaemon : IDaemonService
{

    public bool IsRunning => false;

    public string ServiceName => "HelloWorld Daemon";

    public event EventHandler Starting;
    public event EventHandler Started;
    public event EventHandler Stopping;
    public event EventHandler Stopped;

    public bool Start()
    {
        // Start the daemon
    }

    public bool Stop()
    {
        // Stop the daemon
    }
}

Events

The IDaemonService implementation has four events which daemons are expected to raise. These events allow other modules/services to detect when your daemon has completed the necessary steps to start its services. For example, you may wish to have your daemon only start after a repository service is finished starting up, etc. The events are:

Event	Description
Starting	This event should be fired when your daemon has initiated its startup process.
Started	This event should be fired after your daemon service has completed all necessary startup processes.
Stopping	This event should be fired when your daemon has initiated shutdown. This allows other services to handle that your service(s) may not be available.
Stopped	This event should be fired after your daemon has finished its shutdown process.

Current Status

You should allow other services to detect whether your daemon has completed startup and is currently active. This state is indicated by the IsRunning property.

Start/Stop Methods

The Start() method should, at minimum be implemented as:

public bool Start() {
    // Notify of startup
    this.Starting?.Invoke(this, EventArgs.Empty);
    
    // Do your startup stuff here
    
    // Notify that startup has completed
    this.Started?.Invoke(this, EventArgs.Empty);
    
    // Finally, let the application host know you started up 
    return true;
}

The Stop() method is implemented in a similar manner:

public bool Stop() {
    // Notify of stop
    this.Stopping?.Invoke(this, EventArgs.Empty);
    
    // Do your shutdown stuff
    
    // Notify that shutdown hsa stopped
    this.Stopped?.Invoke(this, EventArgs.Empty);
    
    // Finally let the application host know you shutdown properly
    return true;
}