Asynchronous APIs bring great performance improvements. However they introduce new risks for bugs due to missing await operators. Starting with versions 6.5 and 7.1, NServiceBus comes with a built-in Roslyn analyzer to detect missing awaits on NServiceBus APIs.
Functionality
The analyzer points out missing await operators when using asynchronous methods on the following classes and interfaces:
IMessageHandlerContextIMessageSessionSagaIEndpointInstanceEndpointIUniformSession(from the UniformSession package)
Failing to await or assign the tasks returned by these methods results in the following compile-time error:
NSB0001: A Task returned by an NServiceBus method is not awaited or assigned to a variable.
Limitations
This analyzer inspects only the APIs contained on the classes and interfaces as described in the previous section. Other asynchronous NServiceBus APIs are not analyzed.
The analyzer checks for ignored Tasks returned from the scanned methods. If the Task is assigned to a variable, passed to another method, or has one of its members accessed, the analyzer will not evaluate this Task's usage any further.
Enabling the analyzer
The analyzer is part of the NServiceBus NuGet package and will be automatically installed when referencing the NServiceBus package in a project.
Requirements
The analyzer requires Visual Studio 2015 Update 2 or newer.
The analyzer also works when building a .NET Core application using dotnet build commands, allowing the analyzer to highlight missing await operators in other development environments.
Disabling the analyzer
The analyzer can be disabled in several ways. However, disabling the analyzer is not recommended as it highlights missing await operators, which can cause duplicate messages, message loss, transaction issues, and more.
Disable analyzer warning for a single call site
#pragma warning disable NSB0001
context.Send(message);
#pragma warning restore NSB0001
Disable analyzer warning project-wide
Add a
Additional recommendations
Treat warnings as errors
The C# compiler already contains a set of inspections which can warn about incorrect usage of async and Task-based APIs. It is recommended to treat these warnings as errors to ensure they are not missed accidentally. This feature can be enabled by the project settings or by adding csproj file directly.