Startup Tasks

In many cases, some task needs to be performed automatically as soon as a silo becomes available. Startup Tasks provide this functionality.

Some use cases include, but are not limited to:

• Starting background timers to perform periodic housekeeping tasks
• Pre-loading some cache grains with data downloaded from external backing storage

Any exceptions that are thrown from a startup task during startup will be reported in the silo log and will stop the silo.

This fail-fast approach is the standard way that Orleans handles silo start-up issues, and is intended to allow any problems with silo configuration and/or bootstrap logic to be easily detected during testing phases rather than being silently ignored and causing unexpected problems later in the silo lifecycle.

Configuring Startup Tasks

Startup tasks can be configured using the ISiloHostBuilder either by registering a delegate to be invoked during startup or by registering a implementation of IStartupTask.

Example: Registering a delegate

siloHostBuilder.AddStartupTask(
  async (IServiceProvider services, CancellationToken cancellation) =>
  {
    // Use the service provider to get the grain factory.
    var grainFactory = services.GetRequiredService<IGrainFactory>();

    // Get a reference to a grain and call a method on it.
    var grain = grainFactory.GetGrain<IMyGrain>(0);
    await grain.Initialize();
});

Example: Registering an IStartupTask implementation

First we must define an implementation of IStartupTask:

public class CallGrainStartupTask : IStartupTask
{
    private readonly IGrainFactory grainFactory;

    public CallGrainStartupTask(IGrainFactory grainFactory)
    {
        this.grainFactory = grainFactory;
    }

    public async Task Execute(CancellationToken cancellationToken)
    {
        var grain = this.grainFactory.GetGrain<IMyGrain>(0);
        await grain.Initialize();
    }
}

Then that implementation must be registered with the ISiloHostBuilder:

siloHostBuilder.AddStartupTask<CallGrainStartupTask>();