Blogged: Async Stacks in Rust

One neat result of Rust’s futures and async / await design is that all of the async callers are on the stack below the async callees. In most other languages, only the youngest async callee is on the stack, and none of the async callers. Because the youngest frame is most often not where a bug’s root cause lies, this extra context makes debugging async code easier in Rust.

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Wow! Getting stacks that work is amazing!

Now that C# has put a bunch of work into getting Tasks to have decent exception stack traces it looks something like this:

Microsoft.WindowsAzure.Storage.StorageException:
   at Microsoft.WindowsAzure.Storage.Core.Executor.Executor+<ExecuteAsyncInternal>d__4`1.MoveNext (Microsoft.WindowsAzure.Storage, Version=9.3.2.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at ACTUALLY_MY_CODE
Inner exception System.TimeoutException handled at Microsoft.WindowsAzure.Storage.Core.Executor.Executor+<ExecuteAsyncInternal>d__4`1.MoveNext:
System.Threading.Tasks.TaskCanceledException:
   at System.Net.Http.HttpConnection+<SendAsyncCore>d__61.MoveNext (System.Net.Http, Version=4.2.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1+ConfiguredTaskAwaiter.GetResult (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Net.Http.HttpConnectionPool+<SendWithNtConnectionAuthAsync>d__40.MoveNext (System.Net.Http, Version=4.2.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1+ConfiguredTaskAwaiter.GetResult (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Net.Http.HttpConnectionPool+<SendWithRetryAsync>d__39.MoveNext (System.Net.Http, Version=4.2.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1+ConfiguredTaskAwaiter.GetResult (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Net.Http.RedirectHandler+<SendAsync>d__4.MoveNext (System.Net.Http, Version=4.2.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1+ConfiguredTaskAwaiter.GetResult (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Net.Http.DiagnosticsHandler+<SendAsync>d__2.MoveNext (System.Net.Http, Version=4.2.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1+ConfiguredTaskAwaiter.GetResult (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Net.Http.HttpClient+<FinishSendAsyncUnbuffered>d__63.MoveNext (System.Net.Http, Version=4.2.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at Microsoft.WindowsAzure.Storage.Core.Executor.Executor+<ExecuteAsyncInternal>d__4`1.MoveNext (Microsoft.WindowsAzure.Storage, Version=9.3.2.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35)
Inner exception System.IO.IOException handled at System.Net.Http.HttpConnection+<SendAsyncCore>d__61.MoveNext:
   at System.Net.Sockets.Socket+AwaitableSocketAsyncEventArgs.ThrowException (System.Net.Sockets, Version=4.2.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a)
   at System.Net.Sockets.Socket+AwaitableSocketAsyncEventArgs.GetResult (System.Net.Sockets, Version=4.2.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a)
   at System.Net.Security.SslStreamInternal+<<FillBufferAsync>g__InternalFillBufferAsync|38_0>d`1.MoveNext (System.Net.Security, Version=4.1.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.ConfiguredValueTaskAwaitable`1+ConfiguredValueTaskAwaiter.GetResult (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Net.Security.SslStreamInternal+<ReadAsyncInternal>d__34`1.MoveNext (System.Net.Security, Version=4.1.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Runtime.CompilerServices.ConfiguredValueTaskAwaitable`1+ConfiguredValueTaskAwaiter.GetResult (System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e)
   at System.Net.Http.HttpConnection+<SendAsyncCore>d__61.MoveNext (System.Net.Http, Version=4.2.1.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a)
Inner exception System.Net.Sockets.SocketException handled at System.Net.Sockets.Socket+AwaitableSocketAsyncEventArgs.ThrowException:

Which is usable, but still drastically more ExceptionDispatchInfo.Throw and CompilerServices.TaskAwaiter than I ever want to see.

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