LA0240: Current Task Is Null in a Runtime-Async Method

Cause

A parameter annotated with CurrentTaskAttribute receives the task that the caller of the async method observes, once the method has yielded. PostSharp reads it from the method builder of the state machine that the C# compiler generates.

On .NET 11, when you enable runtime async with <Features>runtime-async=on</Features>, the C# compiler generates no state machine for an async method that returns Task, Task<TResult>, ValueTask or ValueTask<TResult>: the runtime suspends and resumes the method, and it provides no task while the method runs. PostSharp still applies the aspect, but the [CurrentTask] parameter is always null in such a method. PostSharp reports LA0240 on the target method, once for each advice and method, because the same advice receives the task when the method is compiled with a state machine.

When IsRequired is true, PostSharp reports the error LA0239 instead.

This message requires runtime async, which the C# compiler supports only on .NET 11 or later, and the examples of this documentation target .NET 10, so no example can show it.

Resolution

• To get the task, compile the project without runtime async: remove runtime-async=on from the Features property of the project.

  Full screen

  <PropertyGroup>
    <!-- Remove runtime-async=on to get the task in [CurrentTask] parameters. -->
    <Features>runtime-async=on</Features>
  </PropertyGroup>
  

• Or, when the advice does not need the task, handle a null task in the advice, and disable the warning by adding LA0240 to the PostSharpDisabledMessages property of the project.

• Or use a binding that works with runtime async, such as AsyncCallIdAttribute, to correlate the advices of one execution of the method.

See Also

Reference

CurrentTaskAttribute
AsyncCallIdAttribute

Other Resources

Advice Parameters
Semantic Advising of Iterator and Async Methods