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Example of Async Thread Issue

non-Awaited task threads stop executing when api controller returns.

Clone the repo. Open AsyncThreadExample.sln Look at Controllers/ValuesController.cs

note line 73: System.Diagnostics.Debug.WriteLine("DoSomeNonAwaitedAsyncThing end " + DateTime.Now.ToString("HH:mm:ss.fff tt"));

Start the api.

run

Invoke-WebRequest -Uri "http://localhost:63894/api/test/MyAsyncIssueExample" -Body "{ Message: 'Hello World' }" -Method Post

The output will look something like

DoSomeNonAwaitedAsyncThing begin 09:07:18.606 AM
DoSomeNormalAsyncThing begin 09:07:18.688 AM
LogTheMessage: LogTheMessage for DoSomeNonAwaitedAsyncThing 09:07:18.702 AM
LogTheMessage: Hello World 09:07:18.702 AM
DoSomeNormalAsyncThing end 09:07:18.741 AM

Notice DoSomeNormalAsyncThing end 09:07:20.741 AM is missing from the output

Try reducing the await Task.Delay(2000); to await Task.Delay(1); 

DoSomeNonAwaitedAsyncThing begin 09:41:41.243 AM
DoSomeNormalAsyncThing begin 09:41:41.244 AM
LogTheMessage: LogTheMessage for DoSomeNonAwaitedAsyncThing 09:41:41.246 AM
LogTheMessage:  09:41:41.246 AM
DoSomeNormalAsyncThing end 09:41:41.248 AM

Notice output includes DoSomeNormalAsyncThing end this time.

Notice web.config app settings added

  <appSettings>
    <add key="aspnet:UseTaskFriendlySynchronizationContext" value="true"/>
    <add key="aspnet:AllowAsyncDuringSyncStages" value="true"/>

Workarounds

If you make the DoSomeNonAwaitedAsyncThing an Async Void the thread runs to completion. If you wrap the call to DoSomeNonAwaitedAsyncThing in Task.Run the thread runs to completion