Summary
The Wolverine.WolverineHasNotStartedException is a common issue encountered when configuring Wolverine in a.NET background worker project. This exception occurs when the IHost has not been started before attempting to use the Wolverine message bus. In this article, we will explore the root cause, real-world impact, and provide a solution to this problem.
Root Cause
The root cause of this issue is that the IHost is not started before using the Wolverine message bus. This can happen when IHost.Build() is called but not IHost.Start() or IHost.StartAsync(). The key takeaway is that Wolverine requires the host to be started before it can function properly.
Why This Happens in Real Systems
This issue can occur in real systems due to the following reasons:
- Incorrect ordering of host operations: Calling IHost.Build() before IHost.Start() or IHost.StartAsync().
- Missing or incomplete configuration: Failing to configure Wolverine correctly, leading to it not being started with the host.
- Async operation not awaited: Not awaiting the StartAsync() method, causing the host to not be fully started.
Real-World Impact
The real-world impact of this issue can be significant, including:
- System crashes: The application may crash or become unresponsive due to the exception.
- Data loss: Unprocessed messages may be lost, leading to data inconsistencies.
- Performance issues: The system may experience performance degradation due to repeated attempts to use the Wolverine message bus.
Example or Code
var builder = Host.CreateApplicationBuilder(args);
var services = builder.Services;
services.AddHostedService();
builder.UseWolverine(opts =>
{
opts.CodeGeneration.TypeLoadMode = TypeLoadMode.Dynamic;
});
var host = builder.Build();
host.Start(); // Start the host before using Wolverine
host.Run();How Senior Engineers Fix It
Senior engineers fix this issue by ensuring that the IHost is started before using the Wolverine message bus. This can be achieved by:
- Correct ordering of host operations: Calling IHost.Start() or IHost.StartAsync() after IHost.Build().
- Proper configuration: Configuring Wolverine correctly to start with the host.
- Awaiting async operations: Awaiting the StartAsync() method to ensure the host is fully started.
Why Juniors Miss It
Juniors may miss this issue due to:
- Lack of understanding of Wolverine: Not fully understanding how Wolverine works and its dependencies.
- Insufficient knowledge of.NET hosting: Not being familiar with the.NET hosting model and the importance of starting the host.
- Inadequate testing: Not thoroughly testing the application to catch this issue before deployment.