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Analyzer proposal: remove redundant state machine #518
Description
Call out where an async state machine is redundant:
async Task<string> DoSomethingAsync()
{
return await SomethingElseAsync(); // .ConfigureAwait(bool) might be a suffix
}So long as SomethingElseAsync() returns the same type as the caller, you can abbreviate to:
Task<string> DoSomethingAsync()
{
return SomethingElseAsync();
}Above is almost equivalent, but it doesn't guarantee exceptions are caught and returned as exceptions, so strictly speaking this is more equivalent:
Task<string> DoSomethingAsync()
{
try
{
return SomethingElseAsync();
}
catch (Exception ex)
{
return Task.FromException(ex);
}
}Cases that cannot be simplified include;
- more than one await
- The await is not immediately returned (or not the last statement).
- The await appears inside a try block.
- A
using varappears in the method, such that it will be disposed of prior to the returned Task being completed. - The type returned by the called async method is not exactly the same as the type returned from the calling async method. (e.g.
Task<object> FooAsync() => BarAsync();whereBarAsync()returnsTask<string>orValueTask<object>.
Reacted by Dean Faizal, Marius Ungureanu, NN and FXZFun
Activity
mavasani commentedon Sep 17, 2019
Probably should offer 2 code fixes, with an additional comment around the try-catch for the more complex code fix?
drewnoakes commentedon Sep 17, 2019
I generally make this change manually and would appreciate the analyzer, but we should be aware that it changes the debugging experience by removing
DoSomethingAsyncfrom the call stack when the program is executing a continuation inSomethingElseAsync.sharwell commentedon Nov 23, 2019
Removing
asyncalso disables the compiler warning saying a task should be awaited, so you'll definitely want to make sure that analyzer is working well before suggesting thatasyncget removed.paulomorgado commentedon Dec 2, 2019
This is a performance optimization but it causes a change in the stack trace if an exception is thrown.
Check this post from Stephen Cleary (@StephenCleary):
Eliding Async and Await
NN--- commentedon Sep 30, 2020
ReSharper extensiosn ReCommended Extension and AsyncConverter suggesting to remove async/await.
This is indeed changes the stack trace but it is still a useful analysis.