I've just stumbled across a rather dangerous scenario while migrating an ASP.NET application to the async/await model.
The situation is that I made a method async: async Task DoWhateverAsync(), changed the declaration in the interface to Task DoWhateverAsync() and hoped that the compiler would tell me where the code now is wrong, via that Warning. Well, tough luck. Wherever that object gets injected via the interface, the warning doesn't happen. :-(
This is dangerous. Is there any way to check automatically for non-awaited methods that return tasks? I don't mind a few warnings too many, but I wouldn't want to miss one.
Here's an example:
using System.Threading.Tasks;
namespace AsyncAwaitGames
{
// In my real case, that method just returns Task.
public interface ICallee { Task<int> DoSomethingAsync(); }
public class Callee: ICallee
{
public async Task<int> DoSomethingAsync() => await Task.FromResult(0);
}
public class Caller
{
public void DoCall()
{
ICallee xxx = new Callee();
// In my real case, the method just returns Task,
// so there is no type mismatch when assigning a result
// either.
xxx.DoSomethingAsync(); // This is where I had hoped for a warning.
}
}
}
After quite some difficulties with this problem I decided to create an Analyzer with code fix to solve it.
The code is available here:
https://github.com/ykoksen/unused-task-warning
It is also as a NuGet package that can be used as an analyzer for a project (when it is build):
https://www.nuget.org/packages/Lindhart.Analyser.MissingAwaitWarning/#
Furthermore it is also available as a Visual Studio Extension (for 2017). However this only analyses currently open files, so I'd recommend using the NuGet package. The extension is available here (or search for it in Visual Studio):
https://marketplace.visualstudio.com/items?itemName=Lindhart.missingAwaitWarning#overview
The code for the analyzer:
public override void Initialize(AnalysisContext context)
{
context.RegisterSyntaxNodeAction(AnalyseSymbolNode, SyntaxKind.InvocationExpression);
}
private void AnalyseSymbolNode(SyntaxNodeAnalysisContext syntaxNodeAnalysisContext)
{
if (syntaxNodeAnalysisContext.Node is InvocationExpressionSyntax node)
{
if (syntaxNodeAnalysisContext
.SemanticModel
.GetSymbolInfo(node.Expression, syntaxNodeAnalysisContext.CancellationToken)
.Symbol is IMethodSymbol methodSymbol)
{
if (node.Parent is ExpressionStatementSyntax)
{
// Only checks for the two most common awaitable types. In principle this should instead check all types that are awaitable
if (EqualsType(methodSymbol.ReturnType, typeof(Task), typeof(ConfiguredTaskAwaitable)))
{
var diagnostic = Diagnostic.Create(Rule, node.GetLocation(), methodSymbol.ToDisplayString());
syntaxNodeAnalysisContext.ReportDiagnostic(diagnostic);
}
}
}
}
}
/// <summary>
/// Checks if the <paramref name="typeSymbol"/> is one of the types specified
/// </summary>
/// <param name="typeSymbol"></param>
/// <param name="type"></param>
/// <returns></returns>
/// <remarks>This method should probably be rewritten so it doesn't merely compare the names, but instead the actual type.</remarks>
private static bool EqualsType(ITypeSymbol typeSymbol, params Type[] type)
{
var fullSymbolNameWithoutGeneric = $"{typeSymbol.ContainingNamespace.ToDisplayString()}.{typeSymbol.Name}";
return type.Any(x => fullSymbolNameWithoutGeneric.Equals(x.FullName));
}
You have a few options:
This is the simplest "Caveman" solution use the built in VS search functionality (CTRL + SHIFT + F) search in Entire solution, also under Find Options click on the checkbox
Use Regular expression and use this regex: (?<!await|task(.*))\s([_a-zA-Z0-9\.])*Async\( It assumes you post fixed all your async method with the Async keyword and the method call is in one line. If it is not true then do not use it (or add the missing validations to the expression).
Use some 3rd party code analyzer tool, Nuget package. ReSharper is very popular and I believe it able to detect this problems or you can create your own rules.
My choice would be to use Roslyn (#Volker provided one solution). You can create your own rule set with code fix solutions (light bulb icon will show your code fix) so this is the best.
UPDATE: VS 2019 checks for this problem by default and gives warnings.
How to use Roslyn:
You have to install .NET Compiler Platform SDK: from here
Use VS 2017 Version 15.2 (or higher)
Create a new project File -> New -> Project, under the Extensibility group select: Analyzer with Code Fix (Nuget + VSIX) You have to target .NET Framework 4.6.2 to create this project.
You can copy paste the previous solution. Create
[DiagnosticAnalyzer(LanguageNames.CSharp)]
public class AsyncAwaitAnalyzer : DiagnosticAnalyzer
{ ...
}
class with logic, to detect the issue. And create
[ExportCodeFixProvider(LanguageNames.CSharp, Name = nameof(AsyncAwaitCodeFixProvider)), Shared]
public class AsyncAwaitCodeFixProvider : CodeFixProvider
{ ...
}
class to provide fixing suggestions (add await) to the problem.
After a success build you will get your own .wsix package you can install it to your VS instance and after a VS restart is should start pick up the problems.
In the end, we used roslyn to find all instances where a return value of Task or Task<> was ignored:
if (methodSymbol.ReturnType.Equals(syntaxNodeAnalysisContext.SemanticModel.Compilation.GetTypeByMetadataName(typeof(Task).FullName)))
{
// For all such symbols, produce a diagnostic.
var diagnostic = Diagnostic.Create(Rule, node.GetLocation(), methodSymbol.ToDisplayString());
syntaxNodeAnalysisContext.ReportDiagnostic(diagnostic);
}
if (((INamedTypeSymbol) methodSymbol.ReturnType).IsGenericType && ((INamedTypeSymbol) methodSymbol.ReturnType).BaseType.Equals(syntaxNodeAnalysisContext.SemanticModel.Compilation.GetTypeByMetadataName(typeof(Task).FullName)))
{
// For all such symbols, produce a diagnostic.
var diagnostic = Diagnostic.Create(Rule, node.GetLocation(), methodSymbol.ToDisplayString());
syntaxNodeAnalysisContext.ReportDiagnostic(diagnostic);
}
The compiler will emit warning CS4014 but it is only emitted if the calling method is async.
No warning:
Task CallingMethod() {
DoWhateverAsync();
// More code that eventually returns a task.
}
Warning CS4014: Because this call is not awaited, execution of the current method continues before the call is completed. Consider applying the 'await' operator to the result of the call.
async Task CallingMethod() {
DoWhateverAsync();
}
This is not terrible useful in your specific case because you have to find all the places where DoWhateverAsync is called and change them to get the warning and then fix the code. But you wanted to use the compiler warning to find these calls in the first place.
I suggest that you use Visual Studio to find all usages of DoWhateverAsync. You will have to modify the surrounding code anyway either by going through compiler warnings or by working through a list of usages.
You can add a specific warning in VS Project properties as one that throws a compilation error, like described here
You can add a semi-colon separated list of warning codes e.g. CS4014, and the compiler will fail to compile if you're not awaiting an async method.
Here's a screenshot with VS2017:
VS2017 configuration to throw compiler errors for warning CS4014
I found a great Visual Studio extension/NuGet package for this. Saves you having to create your own like other answers suggest.
https://github.com/ykoksen/unused-task-warning
Once I installed the Visual Studio extension I went to Analyze/Run Code Analysis/On Solution and it found several places where I had this issue.
(Sorry if a few parts aren't correct...
I'm a bit of a novice to C# syntax)
I am currently working on a command line project. The project involves creating an algorithm that solves Problem 4 on Project Euler:
https://projecteuler.net/problem=4
From the beginning, ever since I have started the challenges, I've mainly been using Visual Studio to solve them. I've been using a "C# Command Line' type project for the interpretation of information.
Ever since I started using this type of windows form, I've found that as soon as:
static void Main(string[] args)
{
//Insert Code Here...
}
Function finished its events and arguments, it suddenly crashed (well, closed)
I believe that this is because it has and end, it ends itself...
I may be wrong...
In the meantime, I simply used a Thread.Sleep() function as a temporary fix.
How can I solve this problem, and why do you think this is happening?
Thank you!
Try this:
public static void Main(string[] args)
{
try
{
// Your code here
}
catch (Exception ex)
{
// This code will only run if your code fails
Console.WriteLine(ex.ToString()); // Show the exception on the console.
}
Console.ReadKey(); // Make a pause so that the screen does not dissapears when I hit Debug -> Run
}
Try running the project using ctrl + F5 instead of just F5. This is a lot cleaner than adding an unnecessary line to detect keypress at the end of the program IMO
My problem is that my return value seems to disappear after it has exited it's method.
public async Task<string> mMethod(){
// My methods code (creates a string to be used as html is quite large)
return htmlString;
}
when following through on the debugger this method will execute fine and the returned string is exactly what I expect it to be. My problem arises with it's invoking method
public async void setHtml(){
String html = await mMethod(); // Break point here is triggered
// code below this is never used, the application is almost in a state of limbo
}
I'm using Visual Studio 2013 for windows, I'm developing for windows 8.1. This is only happening when I am using debugger, if I start without debugging this problem doesn't happen. Does anyone know whats going wrong or how to fix it?
I seem to have found a soloution although I am not sure why this works if anyone does I would appreciate if they could explain it for me.
When calling mMethod() inserting Task.WaitAny(); above stopped this bug from happening.
public async void setHtml(){
Task.WaitAny();
String html = await mMethod();
//Break point on this line will now activate
}
I am new to programming in c# and I have started to develop a project of around 500 lines. I have many functions and variables declared and iam using comments near the code to make it easy to identify code blocks like:
//code for login button
private void button1_Click(object sender, EventArgs e)
{
}
But this is little difficult for me. Is there any other way in visual studio 2008 that can make my code easy to identify and read? Please help... Thanks.
You should use #region for this.
#region lets you specify a block of code that you can expand or collapse. Its a good option when you want to wrap up your code and give it some name.
#region My wrapped code
public class Sample
{
static void Main()
{
}
}
#endregion
Also you can use outlining feature..
Select the code you want to hide, right click on it and choose "Outlining" - "Hide selection" (Ctrl + M, Ctrl + H). The same result as with regions, but without them.
just type /// ;-)
you can use /* bla bla bla */ too, this is a classic multi-line-comment
When doing a console application in Java with Eclipse, I see the output being put in a text box in the IDE itself, instead of having a console popping up like in Visual Studio. This comes in handy, as even after the program has exited, I can still make good use of the text that was written in it, as it doesn't get erased until I run it again. Is it possible to achieve anything like that with Visual Studio? I know that instead of doing
System.Console.WriteLine(str);
I can do
System.Diagnostics.Debug.WriteLine(str);
but it is not quite the same thing, as you get a lot of "junk" in the Output window, as all the loaded symbols and such.
Even better, is it possible to have everything done in the IDE itself, when you run your application, instead of having the console running?
In the Tools -> Visual Studio Options Dialog -> Debugging -> Check the "Redirect All Output Window Text to the Immediate Window".
In the Visual Studio Options Dialog -> Debugging -> Check the "Redirect All Output Window Text to the Immediate Window". Then go to your project settings and change the type from "Console Application" to "Windows Application". At that point Visual Studio does not open up a console window anymore, and the output is redirected to the Output window in Visual Studio. However, you cannot do anything "creative", like requesting key or text input, or clearing the console - you'll get runtime exceptions.
Use System.Diagnostics.Trace
Depending on what listeners you attach, trace output can go to the debug window, the console, a file, database, or all at once. The possibilities are literally endless, as implementing your own TraceListener is extremely simple.
You can try VSConsole which allow you to integrate its console window inside VisualStudio as dock panel at bottom. To use this you have to
Add VSCodeExtension to VisualStudio
Add VSCode NugetPackage reference in your project.
Add using Console = VSConsole.Console; as namespace reference in *.cs file
change the Output type from Console Application to Windows Application to hide the main console window that pops up when you run your console application.
Then your application will use VSConsole.Console class insted of System.Console class.
It's time to check the latest release/s for Visual Studio, folks. The most suggested solution that did not work for some of you before might work now.
In Visual Studio 2017 (Release Version 15.4.2 and above), going to Tools > Options > Debugging > General > (Check Box) Redirect all Output Window text to Immediate Window has worked for me.
Few Notes:
To see the Immediate Window, make sure that you are in Debugging mode.
There should now be 3 other debugging tools available at your disposal, namely, Call Stack, Breakpoints, and Command Window, as shown below:
Best wishes!
You could create a wrapper application that you run instead of directly running your real app. The wrapper application can listen to stdout and redirect everything to Trace. Then change the run settings to launch your wrapper and pass in the path to the real app to run.
You could also have the wrapper auto-attach the debugger to the new process if a debugger is attached to the wrapper.
A simple solution that works for me, to work with console ability(ReadKey, String with Format and arg etc) and to see and save the output:
I write TextWriter that write to Console and to Trace and replace the Console.Out with it.
if you use Dialog -> Debugging -> Check the "Redirect All Output Window Text to the Immediate Window" you get it in the Immediate Window and pretty clean.
my code:
in start of my code:
Console.SetOut(new TextHelper());
and the class:
public class TextHelper : TextWriter
{
TextWriter console;
public TextHelper() {
console = Console.Out;
}
public override Encoding Encoding => this.console.Encoding;
public override void WriteLine(string format, params object[] arg)
{
string s = string.Format(format, arg);
WriteLine(s);
}
public override void Write(object value)
{
console.Write(value);
System.Diagnostics.Trace.Write(value);
}
public override void WriteLine(object value)
{
Write(value);
Write("\n");
}
public override void WriteLine(string value)
{
console.WriteLine(value);
System.Diagnostics.Trace.WriteLine(value);
}
}
Note: I override just what I needed so if you write other types you should override more
I know this is just another answer, but I thought I'd write something down for the new Web Developers, who might get confused about the "Change to a Windows Application" part, because I think by default an MVC application in Visual Studio 2013 defaults to an Output Type of Class Library.
My Web Application by default is set as an output type of "Class Library." You don't have to change that. All I had to do was follow the suggestions of going to Tools > Options > Debugging > Redirect all Output Window text to the Immediate Window. I then used the System.Diagnostics.Trace suggestion by Joel Coehoorn above.
Instead, you can collect the output in a test result.
You can't supply input, but you can easily provide several tests with different command line arguments, each test collecting the output.
If your goal is debugging, this is a low effort way of offering a repeatable debugging scenario.
namespace Commandline.Test
{
using Microsoft.VisualStudio.TestTools.UnitTesting;
[TestClass]
public class CommandlineTests
{
[TestMethod]
public void RunNoArguments()
{
Commandline.Program.Main(new string[0]);
}
}
}
regarding System.Diagnostics.Debug producing a lot of "junk" in the Output window:
You can turn that off by right clicking in the output window. E.g. there's an item "Module Load Messages" which you want to disable and an item "Program Output" which you want to keep.
You have three possibilities to do this, but it's not trivial.
The main idea of all IDEs is that all of them are the parents of the child (debug) processes. In this case, it is possible to manipulate with standard input, output and error handler. So IDEs start child applications and redirect out into the internal output window. I know about one more possibility, but it will come in future
You could implement your own debug engine for Visual Studio. Debug Engine control starting and debugging for application. Examples for this you could find how to do this on learn.microsoft.com (Visual Studio Debug engine)
Redirect form application using duplication of std handler for c++ or use Console.SetOut(TextWriter) for c#.
If you need to print into the output window you need to use Visual Studio extension SDK.
Example of the second variant you could find on Github.
Start application that uses System.Diagnostics.Debug.WriteLine (for printing into output) and than it will start child application. On starting a child, you need to redirect stdout into parent with pipes. You could find an example on MSDN. But I think this is not the best way.
If you need output from Console.WriteLine, and the Redirect All Output Window Text to the Immediate Window does not function and you need to know the output of Tests from the Integrated Test Explorer, using NUnit.Framework our problem is already solved at VS 2017:
Example taken from C# In Depth by Jon Skeet:
This produce this output at Text Explorer:
When we click on Blue Output, under Elapsed Time, at right, and it produces this:
Standard Output is our desired Output, produced by Console.WriteLine.
It functions for Console and for Windows Form Applications at VS 2017, but only for Output generated for Test Explorer at Debug or Run; anyway, this is my main need of Console.WriteLine output.
If you are using same methods on Console that are available in Debug class like Console.WriteLine(string) then in .net core you can add below line as your 1'st line in program.cs file.
global using Console = System.Diagnostics.Debug;
using System.Diagnostics;
Now all your call for Console.WriteLine(string) are executed as Debug.WriteLine(string) in all *.cs files in project. At places where you want to explicitly use console methods like Console.Readline() then you have to replace it with fully qualified class name System.Console.ReadLine().
Now output from all your Console.WriteLine(string) is now visible in Visualstudio output window. You can further filter out noise in output window by selecting what type of messages you want to see in that window as shown below
Similar to #Sarel Foyerlicht's answer, the only way it work on my side is routing to debug output using this (complete) wrapper.
public class DebugTextWriter : StreamWriter
{
public DebugTextWriter() : base(new DebugOutStream(), System.Text.Encoding.Unicode, 1024) { this.AutoFlush = true; }
sealed class DebugOutStream : Stream
{
public override void Write(byte[] buffer, int offset, int count) { Debug.Write(System.Text.Encoding.Unicode.GetString(buffer, offset, count)); }
public override bool CanRead => false;
public override bool CanSeek => false;
public override bool CanWrite => true;
public override void Flush() => Debug.Flush();
public override long Length => throw new NotImplementedException();
public override int Read(byte[] buffer, int offset, int count) => throw new NotImplementedException();
public override long Seek(long offset, SeekOrigin origin) => throw new NotImplementedException();
public override void SetLength(long value) => throw new NotImplementedException();
public override long Position { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
};
}
which is utilized by rerouting via
System.Console.SetOut(new DebugTextWriter())