async Main wouldn't compile [duplicate]

async Main wouldn't compile [duplicate] - c#

I copied below code from this link.But when I am compiling this code I am getting an entry point cannot be marked with the 'async' modifier. How can I make this code compilable?
class Program
{
static async void Main(string[] args)
{
Task<string> getWebPageTask = GetWebPageAsync("http://msdn.microsoft.com");
Debug.WriteLine("In startButton_Click before await");
string webText = await getWebPageTask;
Debug.WriteLine("Characters received: " + webText.Length.ToString());
}
private static async Task<string> GetWebPageAsync(string url)
{
// Start an async task.
Task<string> getStringTask = (new HttpClient()).GetStringAsync(url);
// Await the task. This is what happens:
// 1. Execution immediately returns to the calling method, returning a
// different task from the task created in the previous statement.
// Execution in this method is suspended.
// 2. When the task created in the previous statement completes, the
// result from the GetStringAsync method is produced by the Await
// statement, and execution continues within this method.
Debug.WriteLine("In GetWebPageAsync before await");
string webText = await getStringTask;
Debug.WriteLine("In GetWebPageAsync after await");
return webText;
}
// Output:
// In GetWebPageAsync before await
// In startButton_Click before await
// In GetWebPageAsync after await
// Characters received: 44306
}

The error message is exactly right: the Main() method cannot be async, because when Main() returns, the application usually ends.
If you want to make a console application that uses async, a simple solution is to create an async version of Main() and synchronously Wait() on that from the real Main():
static void Main()
{
MainAsync().Wait();
}
static async Task MainAsync()
{
// your async code here
}
This is one of the rare cases where mixing await and Wait() is a good idea, you shouldn't usually do that.
Update: Async Main is supported in C# 7.1.

Starting from C# 7.1 there are 4 new signatures for Main method which allow to make it async(Source, Source 2, Source 3):
public static Task Main();
public static Task<int> Main();
public static Task Main(string[] args);
public static Task<int> Main(string[] args);
You can mark your Main method with async keyword and use await inside Main:
static async Task Main(string[] args)
{
Task<string> getWebPageTask = GetWebPageAsync("http://msdn.microsoft.com");
Debug.WriteLine("In startButton_Click before await");
string webText = await getWebPageTask;
Debug.WriteLine("Characters received: " + webText.Length.ToString());
}
C# 7.1 is available in Visual Studio 2017 15.3.

I'm using C# 8 and its working fine.
static async Task Main(string[] args)
{
var response = await SomeAsyncFunc();
Console.WriteLine("Async response", response);
}
OR without "await" keyword.
static void Main(string[] args)
{
var response = SomeAsyncFunc().GetAwaiter().GetResult();
Console.WriteLine("Async response", response);
}

The difference between the code in the link's example and yours, is that you're trying to mark the Main() method with an async modifier - this is not allowed, and the error says that exactly - the Main() method is the "entry point" to the application (it's the method that is executed when your application starts), and it's not allowed to be async.

Wrap your async code in MainAsync() - which is an async function
then call MainAsync().GetAwaiter().GetResult();

Related

Not valid entry point c# http client [duplicate]

I am new to asynchronous programming with the async modifier. I am trying to figure out how to make sure that my Main method of a console application actually runs asynchronously.
class Program
{
static void Main(string[] args)
{
Bootstrapper bs = new Bootstrapper();
var list = bs.GetList();
}
}
public class Bootstrapper {
public async Task<List<TvChannel>> GetList()
{
GetPrograms pro = new GetPrograms();
return await pro.DownloadTvChannels();
}
}
I know this is not running asynchronously from "the top." Since it is not possible to specify the async modifier on the Main method, how can I run code within main asynchronously?

As you discovered, in VS11 the compiler will disallow an async Main method. This was allowed (but never recommended) in VS2010 with the Async CTP.
Update, 2017-11-30: As of Visual Studio 2017 Update 3 (15.3), the language now supports an async Main - as long as it returns Task or Task<T>. So you can now do this:
class Program
{
static async Task Main(string[] args)
{
Bootstrapper bs = new Bootstrapper();
var list = await bs.GetList();
}
}
The semantics appear to be the same as the GetAwaiter().GetResult() style of blocking the main thread. However, there's no language spec for C# 7.1 yet, so this is only an assumption.
I have recent blog posts about async/await and asynchronous console programs in particular. Here's some background info from the intro post:
If "await" sees that the awaitable has not completed, then it acts asynchronously. It tells the awaitable to run the remainder of the method when it completes, and then returns from the async method. Await will also capture the current context when it passes the remainder of the method to the awaitable.
Later on, when the awaitable completes, it will execute the remainder of the async method (within the captured context).
Here's why this is a problem in Console programs with an async Main:
Remember from our intro post that an async method will return to its caller before it is complete. This works perfectly in UI applications (the method just returns to the UI event loop) and ASP.NET applications (the method returns off the thread but keeps the request alive). It doesn't work out so well for Console programs: Main returns to the OS - so your program exits.
One solution is to provide your own context - a "main loop" for your console program that is async-compatible.
If you have a machine with the Async CTP, you can use GeneralThreadAffineContext from My Documents\Microsoft Visual Studio Async CTP\Samples(C# Testing) Unit Testing\AsyncTestUtilities. Alternatively, you can use AsyncContext from my Nito.AsyncEx NuGet package.
Here's an example using AsyncContext; GeneralThreadAffineContext has almost identical usage:
using Nito.AsyncEx;
class Program
{
static void Main(string[] args)
{
AsyncContext.Run(() => MainAsync(args));
}
static async void MainAsync(string[] args)
{
Bootstrapper bs = new Bootstrapper();
var list = await bs.GetList();
}
}
Alternatively, you can just block the main Console thread until your asynchronous work has completed:
class Program
{
static void Main(string[] args)
{
MainAsync(args).GetAwaiter().GetResult();
}
static async Task MainAsync(string[] args)
{
Bootstrapper bs = new Bootstrapper();
var list = await bs.GetList();
}
}
Note the use of GetAwaiter().GetResult(); this avoids the AggregateException wrapping that happens if you use Wait() or Result.

You can solve this with this simple construct:
class Program
{
static void Main(string[] args)
{
Task.Run(async () =>
{
// Do any async anything you need here without worry
}).GetAwaiter().GetResult();
}
}
That will put everything you do out on the ThreadPool where you'd want it (so other Tasks you start/await don't attempt to rejoin a Thread they shouldn't), and wait until everything's done before closing the Console app. No need for special loops or outside libs.
Edit: Incorporate Andrew's solution for uncaught Exceptions.

You can do this without needing external libraries also by doing the following:
class Program
{
static void Main(string[] args)
{
Bootstrapper bs = new Bootstrapper();
var getListTask = bs.GetList(); // returns the Task<List<TvChannel>>
Task.WaitAll(getListTask); // block while the task completes
var list = getListTask.Result;
}
}

In C# 7.1 you will be able to do a proper async Main. The appropriate signatures for Main method has been extended to:
public static Task Main();
public static Task<int> Main();
public static Task Main(string[] args);
public static Task<int> Main(string[] args);
For e.g. you could be doing:
static async Task Main(string[] args)
{
Bootstrapper bs = new Bootstrapper();
var list = await bs.GetList();
}
At compile time, the async entry point method will be translated to call GetAwaitor().GetResult().
Details: https://blogs.msdn.microsoft.com/mazhou/2017/05/30/c-7-series-part-2-async-main
EDIT:
To enable C# 7.1 language features, you need to right-click on the project and click "Properties" then go to the "Build" tab. There, click the advanced button at the bottom:
From the language version drop-down menu, select "7.1" (or any higher value):
The default is "latest major version" which would evaluate (at the time of this writing) to C# 7.0, which does not support async main in console apps.

I'll add an important feature that all of the other answers have overlooked: cancellation.
One of the big things in TPL is cancellation support, and console apps have a method of cancellation built in (CTRL+C). It's very simple to bind them together. This is how I structure all of my async console apps:
static void Main(string[] args)
{
CancellationTokenSource cts = new CancellationTokenSource();
System.Console.CancelKeyPress += (s, e) =>
{
e.Cancel = true;
cts.Cancel();
};
MainAsync(args, cts.Token).GetAwaiter.GetResult();
}
static async Task MainAsync(string[] args, CancellationToken token)
{
...
}

C# 7.1 (using vs 2017 update 3) introduces async main
You can write:
static async Task Main(string[] args)
{
await ...
}
For more details C# 7 Series, Part 2: Async Main
Update:
You may get a compilation error:
Program does not contain a static 'Main' method suitable for an entry point
This error is due to that vs2017.3 is configured by default as c#7.0 not c#7.1.
You should explicitly modify the setting of your project to set c#7.1 features.
You can set c#7.1 by two methods:
Method 1: Using the project settings window:
Open the settings of your project
Select the Build tab
Click the Advanced button
Select the version you want
As shown in the following figure:
Method2: Modify PropertyGroup of .csproj manually
Add this property:
<LangVersion>7.1</LangVersion>
example:
<PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
<PlatformTarget>AnyCPU</PlatformTarget>
<DebugSymbols>true</DebugSymbols>
<DebugType>full</DebugType>
<Optimize>false</Optimize>
<OutputPath>bin\Debug\</OutputPath>
<DefineConstants>DEBUG;TRACE</DefineConstants>
<ErrorReport>prompt</ErrorReport>
<WarningLevel>4</WarningLevel>
<Prefer32Bit>false</Prefer32Bit>
<LangVersion>7.1</LangVersion>
</PropertyGroup>

If you're using C# 7.1 or later, go with the nawfal's answer and just change the return type of your Main method to Task or Task<int>. If you are not:
Have an async Task MainAsync like Johan said.
Call its .GetAwaiter().GetResult() to catch the underlying exception like do0g said.
Support cancellation like Cory said.
A second CTRL+C should terminate the process immediately. (Thanks binki!)
Handle OperationCancelledException - return an appropriate error code.
The final code looks like:
private static int Main(string[] args)
{
var cts = new CancellationTokenSource();
Console.CancelKeyPress += (s, e) =>
{
e.Cancel = !cts.IsCancellationRequested;
cts.Cancel();
};
try
{
return MainAsync(args, cts.Token).GetAwaiter().GetResult();
}
catch (OperationCanceledException)
{
return 1223; // Cancelled.
}
}
private static async Task<int> MainAsync(string[] args, CancellationToken cancellationToken)
{
// Your code...
return await Task.FromResult(0); // Success.
}

Haven't needed this much yet, but when I've used console application for Quick tests and required async I've just solved it like this:
class Program
{
static void Main(string[] args)
{
MainAsync(args).Wait();
}
static async Task MainAsync(string[] args)
{
// Code here
}
}

For asynchronously calling task from Main, use
Task.Run() for .NET 4.5
Task.Factory.StartNew() for .NET 4.0 (May require Microsoft.Bcl.Async library for async and await keywords)
Details:
http://blogs.msdn.com/b/pfxteam/archive/2011/10/24/10229468.aspx

In Main try changing the call to GetList to:
Task.Run(() => bs.GetList());

When the C# 5 CTP was introduced, you certainly could mark Main with async... although it was generally not a good idea to do so. I believe this was changed by the release of VS 2013 to become an error.
Unless you've started any other foreground threads, your program will exit when Main completes, even if it's started some background work.
What are you really trying to do? Note that your GetList() method really doesn't need to be async at the moment - it's adding an extra layer for no real reason. It's logically equivalent to (but more complicated than):
public Task<List<TvChannel>> GetList()
{
return new GetPrograms().DownloadTvChannels();
}

Newest version of C# - C# 7.1 allows to create async console app. To enable C# 7.1 in project, you have to upgrade your VS to at least 15.3, and change C# version to C# 7.1 or C# latest minor version. To do this, go to Project properties -> Build -> Advanced -> Language version.
After this, following code will work:
internal class Program
{
public static async Task Main(string[] args)
{
(...)
}

As of C# 7.1 the following signatures are valid for the Main method.
public static void Main() { }
public static int Main() { }
public static void Main(string[] args) { }
public static int Main(string[] args) { }
public static async Task Main() { }
public static async Task<int> Main() { }
public static async Task Main(string[] args) { }
public static async Task<int> Main(string[] args) { }
So, now you can do async/await
static async Task Main(string[] args)
{
Console.WriteLine("Hello Asyn Main method!");
await Task.Delay(200);
}

On MSDN, the documentation for Task.Run Method (Action) provides this example which shows how to run a method asynchronously from main:
using System;
using System.Threading;
using System.Threading.Tasks;
public class Example
{
public static void Main()
{
ShowThreadInfo("Application");
var t = Task.Run(() => ShowThreadInfo("Task") );
t.Wait();
}
static void ShowThreadInfo(String s)
{
Console.WriteLine("{0} Thread ID: {1}",
s, Thread.CurrentThread.ManagedThreadId);
}
}
// The example displays the following output:
// Application thread ID: 1
// Task thread ID: 3
Note this statement that follows the example:
The examples show that the asynchronous task executes on a different
thread than the main application thread.
So, if instead you want the task to run on the main application thread, see the answer by #StephenCleary.
And regarding the thread on which the task runs, also note Stephen's comment on his answer:
You can use a simple Wait or Result, and there's nothing wrong
with that. But be aware that there are two important differences: 1)
all async continuations run on the thread pool rather than the main
thread, and 2) any exceptions are wrapped in an AggregateException.
(See Exception Handling (Task Parallel Library) for how to incorporate exception handling to deal with an AggregateException.)
Finally, on MSDN from the documentation for Task.Delay Method (TimeSpan), this example shows how to run an asynchronous task that returns a value:
using System;
using System.Threading.Tasks;
public class Example
{
public static void Main()
{
var t = Task.Run(async delegate
{
await Task.Delay(TimeSpan.FromSeconds(1.5));
return 42;
});
t.Wait();
Console.WriteLine("Task t Status: {0}, Result: {1}",
t.Status, t.Result);
}
}
// The example displays the following output:
// Task t Status: RanToCompletion, Result: 42
Note that instead of passing a delegate to Task.Run, you can instead pass a lambda function like this:
var t = Task.Run(async () =>
{
await Task.Delay(TimeSpan.FromSeconds(1.5));
return 42;
});

In my case I had a list of jobs that I wanted to run in async from my main method, have been using this in production for quite sometime and works fine.
static void Main(string[] args)
{
Task.Run(async () => { await Task.WhenAll(jobslist.Select(nl => RunMulti(nl))); }).GetAwaiter().GetResult();
}
private static async Task RunMulti(List<string> joblist)
{
await ...
}

To avoid freezing when you call a function somewhere down the call stack that tries to re-join the current thread (which is stuck in a Wait), you need to do the following:
class Program
{
static void Main(string[] args)
{
Bootstrapper bs = new Bootstrapper();
List<TvChannel> list = Task.Run((Func<Task<List<TvChannel>>>)bs.GetList).Result;
}
}
(the cast is only required to resolve ambiguity)

class Program
{
public static EventHandler AsyncHandler;
static void Main(string[] args)
{
AsyncHandler+= async (sender, eventArgs) => { await AsyncMain(); };
AsyncHandler?.Invoke(null, null);
}
private async Task AsyncMain()
{
//Your Async Code
}
}

This is hypothetical but I am thinking:
static void Main(string[] args)
{
var context = new Thread(() => /*do stuff*/);
context.Start();
context.Join();
}

Not sure if this is what you're looking for, but I wanted to await a method on load. I ended up using the Main_Shown handler and making it async:
private async void Main_Shown(object sender, EventArgs e)
{
await myAsyncMethod();
}

The following code can be used to make a main async. I've tweak it to use long running tasks (learn more here: https://learn.microsoft.com/en-us/dotnet/api/system.threading.tasks.taskcreationoptions?view=net-7.0)
It's also implementing the cancellation token from the above response.
private static int Main(string[] args)
{
var cts = new CancellationTokenSource();
Console.CancelKeyPress += (s, e) =>
{
e.Cancel = !cts.IsCancellationRequested;
cts.Cancel();
Console.WriteLine("CancellationRequested");
};
try
{
var task = new Task<int>(
() => MainAsync(args, cts.Token).GetAwaiter().GetResult(),
cts.Token,
TaskCreationOptions.LongRunning //https://learn.microsoft.com/en-us/dotnet/api/system.threading.tasks.taskcreationoptions?view=net-7.0
);
task.Start();
var exitCode = task.GetAwaiter().GetResult();
/*Or this.*/
//var exitCode = MainAsync(args, cts.Token).GetAwaiter().GetResult();
return exitCode;// MainAsync(args, cts.Token).GetAwaiter().GetResult();
}
catch (OperationCanceledException ex)
{
Console.WriteLine(ex);
return 1223; // Cancelled.
}
catch(Exception ex)
{
Console.WriteLine(ex);
return -1;
}
}
private static async Task<int> MainAsync(string[] args, CancellationToken cancellationToken)
{
await Something()
return;
}
In the following example I wrote. You can play with maxDegreeOfParallelism & numberOfIteration to understand / see how the task are handle. Good statring point for learning TPL!
private static async Task<int> MainAsync(string[] args, CancellationToken cancellationToken)
{
var infos = new ConcurrentBag<Info>();
var mySuperUselessService = new BigWorkload();
int numberOfSecond = 1;
int numberOfIteration = 25; //Experiment with this
int maxDegreeOfParallelism = 4; //Experiment with this
var simulateWorkTime = TimeSpan.FromSeconds(numberOfSecond);
var informations = Enumerable.Range(1, numberOfIteration)
.Select(x => new Info() { Index = x });
var count = informations.Count();
var chunkNeeded = Math.Round(count / Convert.ToDecimal(maxDegreeOfParallelism), MidpointRounding.ToPositiveInfinity);
var splashInfo = #$"
Press CTRL + C to cancel.
Processing {count} items, maxDegreeOfParallelism set to {maxDegreeOfParallelism}.
But it will be bound by the core on the machine {Environment.ProcessorCount}.
This operation should take ~{chunkNeeded * (numberOfSecond + 0.01m)}s
And will be starting test in 2s
";
Console.WriteLine(splashInfo);
await Task.Delay(TimeSpan.FromSeconds(2));
var parralelOptions = new ParallelOptions() { MaxDegreeOfParallelism = maxDegreeOfParallelism, CancellationToken = cancellationToken};
var stopwatch = new Stopwatch();
stopwatch.Start();
var forLoopTask = Parallel.ForEachAsync(informations, parralelOptions, async (info, token) =>
{
await mySuperUselessService.Simulate(simulateWorkTime, info);
Console.WriteLine(info);
infos.Add(info);
});
await forLoopTask;
stopwatch.Stop();
foreach (var grouped in infos.GroupBy(x => x.ManagedThreadId))
{
Console.WriteLine($"ThreadId: {grouped.Key}");
foreach (var item in grouped)
{
Console.WriteLine($"\t Index: {item.Index} {item.TaskCurrentId}");
}
}
Console.WriteLine($"NumberOfThread: {infos.GroupBy(x => x.ManagedThreadId).Count()}");
Console.WriteLine($"Elasped: {stopwatch.ElapsedMilliseconds / 1000d}s");
Console.WriteLine(splashInfo);
return 0;
}

console application and async await example is blocking

Why is the following example blocking? I was expecting "Run First" to run immediately and then 5 seconds later the "Run Last" would appear.
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
// Call SomeAsyncCode() somehow
SomeAsyncCode().GetAwaiter().GetResult();
Console.WriteLine("Run First");
}
private static async Task SomeAsyncCode()
{
// Use await here!
await Task.Delay(5000);
Console.WriteLine("Run Last");
// Other async goodness...
}
}
}

You are awaiting (term used loosely) the task.
It would make more sense if you didn't use .GetAwaiter().GetResult(); (which are internal framework methods anyway) and just wrote
SomeAsyncCode().Wait();
Console.WriteLine("Run First");
It then becomes obvious whats happening, you are waiting for the task to complete.
The following is probably more like what you expect;
// start task
var task = SomeAsyncCode();
Console.WriteLine("Run First");
task.Wait();
In all honesty though, it should be rare to need to call, Wait, Result or GetAwaiter().GetResult() on an async method, doing so in a UI app, or something with a Synchronization Context will likely cause a deadlock
Ideally you let async and await propagate, in C# 7.1 and higher you have the ability to create an async Entry Point which allows you use the Async and Await Pattern in a more succinct manner
static async Task Main(string[] args)
{
await SomeAsyncCode();
Console.WriteLine("Run First");
}
or
static async Task Main(string[] args)
{
var task = SomeAsyncCode();
Console.WriteLine("Run First");
await Task.WhenAll(task);
}

When you define async Task Method() - you are telling that this method should be awaited even though it will return nothing.
When you define async void Method() - you are telling that this is fire'n'forget method and you don't want to await it.
Also, when you void Main(string[] args) is returning - your application is closing and GC will kill all your tasks.
So, your code should be more like this:
static void Main(string[] args)
{
// Call SomeAsyncCode() somehow
SomeAsyncCode();
Console.WriteLine("Run First");
Console.ReadKey(); // you need this to prevent app from closing
}
private static async void SomeAsyncCode()
{
// Use await here!
await Task.Delay(5000);
Console.WriteLine("Run Last");
// Other async goodness...
}

Awaiting SQL client async in the Main Method [duplicate]

I am new to asynchronous programming with the async modifier. I am trying to figure out how to make sure that my Main method of a console application actually runs asynchronously.
class Program
{
static void Main(string[] args)
{
Bootstrapper bs = new Bootstrapper();
var list = bs.GetList();
}
}
public class Bootstrapper {
public async Task<List<TvChannel>> GetList()
{
GetPrograms pro = new GetPrograms();
return await pro.DownloadTvChannels();
}
}
I know this is not running asynchronously from "the top." Since it is not possible to specify the async modifier on the Main method, how can I run code within main asynchronously?

As you discovered, in VS11 the compiler will disallow an async Main method. This was allowed (but never recommended) in VS2010 with the Async CTP.
Update, 2017-11-30: As of Visual Studio 2017 Update 3 (15.3), the language now supports an async Main - as long as it returns Task or Task<T>. So you can now do this:
class Program
{
static async Task Main(string[] args)
{
Bootstrapper bs = new Bootstrapper();
var list = await bs.GetList();
}
}
The semantics appear to be the same as the GetAwaiter().GetResult() style of blocking the main thread. However, there's no language spec for C# 7.1 yet, so this is only an assumption.
I have recent blog posts about async/await and asynchronous console programs in particular. Here's some background info from the intro post:
If "await" sees that the awaitable has not completed, then it acts asynchronously. It tells the awaitable to run the remainder of the method when it completes, and then returns from the async method. Await will also capture the current context when it passes the remainder of the method to the awaitable.
Later on, when the awaitable completes, it will execute the remainder of the async method (within the captured context).
Here's why this is a problem in Console programs with an async Main:
Remember from our intro post that an async method will return to its caller before it is complete. This works perfectly in UI applications (the method just returns to the UI event loop) and ASP.NET applications (the method returns off the thread but keeps the request alive). It doesn't work out so well for Console programs: Main returns to the OS - so your program exits.
One solution is to provide your own context - a "main loop" for your console program that is async-compatible.
If you have a machine with the Async CTP, you can use GeneralThreadAffineContext from My Documents\Microsoft Visual Studio Async CTP\Samples(C# Testing) Unit Testing\AsyncTestUtilities. Alternatively, you can use AsyncContext from my Nito.AsyncEx NuGet package.
Here's an example using AsyncContext; GeneralThreadAffineContext has almost identical usage:
using Nito.AsyncEx;
class Program
{
static void Main(string[] args)
{
AsyncContext.Run(() => MainAsync(args));
}
static async void MainAsync(string[] args)
{
Bootstrapper bs = new Bootstrapper();
var list = await bs.GetList();
}
}
Alternatively, you can just block the main Console thread until your asynchronous work has completed:
class Program
{
static void Main(string[] args)
{
MainAsync(args).GetAwaiter().GetResult();
}
static async Task MainAsync(string[] args)
{
Bootstrapper bs = new Bootstrapper();
var list = await bs.GetList();
}
}
Note the use of GetAwaiter().GetResult(); this avoids the AggregateException wrapping that happens if you use Wait() or Result.

You can solve this with this simple construct:
class Program
{
static void Main(string[] args)
{
Task.Run(async () =>
{
// Do any async anything you need here without worry
}).GetAwaiter().GetResult();
}
}
That will put everything you do out on the ThreadPool where you'd want it (so other Tasks you start/await don't attempt to rejoin a Thread they shouldn't), and wait until everything's done before closing the Console app. No need for special loops or outside libs.
Edit: Incorporate Andrew's solution for uncaught Exceptions.

You can do this without needing external libraries also by doing the following:
class Program
{
static void Main(string[] args)
{
Bootstrapper bs = new Bootstrapper();
var getListTask = bs.GetList(); // returns the Task<List<TvChannel>>
Task.WaitAll(getListTask); // block while the task completes
var list = getListTask.Result;
}
}

In C# 7.1 you will be able to do a proper async Main. The appropriate signatures for Main method has been extended to:
public static Task Main();
public static Task<int> Main();
public static Task Main(string[] args);
public static Task<int> Main(string[] args);
For e.g. you could be doing:
static async Task Main(string[] args)
{
Bootstrapper bs = new Bootstrapper();
var list = await bs.GetList();
}
At compile time, the async entry point method will be translated to call GetAwaitor().GetResult().
Details: https://blogs.msdn.microsoft.com/mazhou/2017/05/30/c-7-series-part-2-async-main
EDIT:
To enable C# 7.1 language features, you need to right-click on the project and click "Properties" then go to the "Build" tab. There, click the advanced button at the bottom:
From the language version drop-down menu, select "7.1" (or any higher value):
The default is "latest major version" which would evaluate (at the time of this writing) to C# 7.0, which does not support async main in console apps.

I'll add an important feature that all of the other answers have overlooked: cancellation.
One of the big things in TPL is cancellation support, and console apps have a method of cancellation built in (CTRL+C). It's very simple to bind them together. This is how I structure all of my async console apps:
static void Main(string[] args)
{
CancellationTokenSource cts = new CancellationTokenSource();
System.Console.CancelKeyPress += (s, e) =>
{
e.Cancel = true;
cts.Cancel();
};
MainAsync(args, cts.Token).GetAwaiter.GetResult();
}
static async Task MainAsync(string[] args, CancellationToken token)
{
...
}

C# 7.1 (using vs 2017 update 3) introduces async main
You can write:
static async Task Main(string[] args)
{
await ...
}
For more details C# 7 Series, Part 2: Async Main
Update:
You may get a compilation error:
Program does not contain a static 'Main' method suitable for an entry point
This error is due to that vs2017.3 is configured by default as c#7.0 not c#7.1.
You should explicitly modify the setting of your project to set c#7.1 features.
You can set c#7.1 by two methods:
Method 1: Using the project settings window:
Open the settings of your project
Select the Build tab
Click the Advanced button
Select the version you want
As shown in the following figure:
Method2: Modify PropertyGroup of .csproj manually
Add this property:
<LangVersion>7.1</LangVersion>
example:
<PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
<PlatformTarget>AnyCPU</PlatformTarget>
<DebugSymbols>true</DebugSymbols>
<DebugType>full</DebugType>
<Optimize>false</Optimize>
<OutputPath>bin\Debug\</OutputPath>
<DefineConstants>DEBUG;TRACE</DefineConstants>
<ErrorReport>prompt</ErrorReport>
<WarningLevel>4</WarningLevel>
<Prefer32Bit>false</Prefer32Bit>
<LangVersion>7.1</LangVersion>
</PropertyGroup>

If you're using C# 7.1 or later, go with the nawfal's answer and just change the return type of your Main method to Task or Task<int>. If you are not:
Have an async Task MainAsync like Johan said.
Call its .GetAwaiter().GetResult() to catch the underlying exception like do0g said.
Support cancellation like Cory said.
A second CTRL+C should terminate the process immediately. (Thanks binki!)
Handle OperationCancelledException - return an appropriate error code.
The final code looks like:
private static int Main(string[] args)
{
var cts = new CancellationTokenSource();
Console.CancelKeyPress += (s, e) =>
{
e.Cancel = !cts.IsCancellationRequested;
cts.Cancel();
};
try
{
return MainAsync(args, cts.Token).GetAwaiter().GetResult();
}
catch (OperationCanceledException)
{
return 1223; // Cancelled.
}
}
private static async Task<int> MainAsync(string[] args, CancellationToken cancellationToken)
{
// Your code...
return await Task.FromResult(0); // Success.
}

Haven't needed this much yet, but when I've used console application for Quick tests and required async I've just solved it like this:
class Program
{
static void Main(string[] args)
{
MainAsync(args).Wait();
}
static async Task MainAsync(string[] args)
{
// Code here
}
}

For asynchronously calling task from Main, use
Task.Run() for .NET 4.5
Task.Factory.StartNew() for .NET 4.0 (May require Microsoft.Bcl.Async library for async and await keywords)
Details:
http://blogs.msdn.com/b/pfxteam/archive/2011/10/24/10229468.aspx

In Main try changing the call to GetList to:
Task.Run(() => bs.GetList());

When the C# 5 CTP was introduced, you certainly could mark Main with async... although it was generally not a good idea to do so. I believe this was changed by the release of VS 2013 to become an error.
Unless you've started any other foreground threads, your program will exit when Main completes, even if it's started some background work.
What are you really trying to do? Note that your GetList() method really doesn't need to be async at the moment - it's adding an extra layer for no real reason. It's logically equivalent to (but more complicated than):
public Task<List<TvChannel>> GetList()
{
return new GetPrograms().DownloadTvChannels();
}

Newest version of C# - C# 7.1 allows to create async console app. To enable C# 7.1 in project, you have to upgrade your VS to at least 15.3, and change C# version to C# 7.1 or C# latest minor version. To do this, go to Project properties -> Build -> Advanced -> Language version.
After this, following code will work:
internal class Program
{
public static async Task Main(string[] args)
{
(...)
}

As of C# 7.1 the following signatures are valid for the Main method.
public static void Main() { }
public static int Main() { }
public static void Main(string[] args) { }
public static int Main(string[] args) { }
public static async Task Main() { }
public static async Task<int> Main() { }
public static async Task Main(string[] args) { }
public static async Task<int> Main(string[] args) { }
So, now you can do async/await
static async Task Main(string[] args)
{
Console.WriteLine("Hello Asyn Main method!");
await Task.Delay(200);
}

On MSDN, the documentation for Task.Run Method (Action) provides this example which shows how to run a method asynchronously from main:
using System;
using System.Threading;
using System.Threading.Tasks;
public class Example
{
public static void Main()
{
ShowThreadInfo("Application");
var t = Task.Run(() => ShowThreadInfo("Task") );
t.Wait();
}
static void ShowThreadInfo(String s)
{
Console.WriteLine("{0} Thread ID: {1}",
s, Thread.CurrentThread.ManagedThreadId);
}
}
// The example displays the following output:
// Application thread ID: 1
// Task thread ID: 3
Note this statement that follows the example:
The examples show that the asynchronous task executes on a different
thread than the main application thread.
So, if instead you want the task to run on the main application thread, see the answer by #StephenCleary.
And regarding the thread on which the task runs, also note Stephen's comment on his answer:
You can use a simple Wait or Result, and there's nothing wrong
with that. But be aware that there are two important differences: 1)
all async continuations run on the thread pool rather than the main
thread, and 2) any exceptions are wrapped in an AggregateException.
(See Exception Handling (Task Parallel Library) for how to incorporate exception handling to deal with an AggregateException.)
Finally, on MSDN from the documentation for Task.Delay Method (TimeSpan), this example shows how to run an asynchronous task that returns a value:
using System;
using System.Threading.Tasks;
public class Example
{
public static void Main()
{
var t = Task.Run(async delegate
{
await Task.Delay(TimeSpan.FromSeconds(1.5));
return 42;
});
t.Wait();
Console.WriteLine("Task t Status: {0}, Result: {1}",
t.Status, t.Result);
}
}
// The example displays the following output:
// Task t Status: RanToCompletion, Result: 42
Note that instead of passing a delegate to Task.Run, you can instead pass a lambda function like this:
var t = Task.Run(async () =>
{
await Task.Delay(TimeSpan.FromSeconds(1.5));
return 42;
});

In my case I had a list of jobs that I wanted to run in async from my main method, have been using this in production for quite sometime and works fine.
static void Main(string[] args)
{
Task.Run(async () => { await Task.WhenAll(jobslist.Select(nl => RunMulti(nl))); }).GetAwaiter().GetResult();
}
private static async Task RunMulti(List<string> joblist)
{
await ...
}

To avoid freezing when you call a function somewhere down the call stack that tries to re-join the current thread (which is stuck in a Wait), you need to do the following:
class Program
{
static void Main(string[] args)
{
Bootstrapper bs = new Bootstrapper();
List<TvChannel> list = Task.Run((Func<Task<List<TvChannel>>>)bs.GetList).Result;
}
}
(the cast is only required to resolve ambiguity)

class Program
{
public static EventHandler AsyncHandler;
static void Main(string[] args)
{
AsyncHandler+= async (sender, eventArgs) => { await AsyncMain(); };
AsyncHandler?.Invoke(null, null);
}
private async Task AsyncMain()
{
//Your Async Code
}
}

This is hypothetical but I am thinking:
static void Main(string[] args)
{
var context = new Thread(() => /*do stuff*/);
context.Start();
context.Join();
}

Not sure if this is what you're looking for, but I wanted to await a method on load. I ended up using the Main_Shown handler and making it async:
private async void Main_Shown(object sender, EventArgs e)
{
await myAsyncMethod();
}

The following code can be used to make a main async. I've tweak it to use long running tasks (learn more here: https://learn.microsoft.com/en-us/dotnet/api/system.threading.tasks.taskcreationoptions?view=net-7.0)
It's also implementing the cancellation token from the above response.
private static int Main(string[] args)
{
var cts = new CancellationTokenSource();
Console.CancelKeyPress += (s, e) =>
{
e.Cancel = !cts.IsCancellationRequested;
cts.Cancel();
Console.WriteLine("CancellationRequested");
};
try
{
var task = new Task<int>(
() => MainAsync(args, cts.Token).GetAwaiter().GetResult(),
cts.Token,
TaskCreationOptions.LongRunning //https://learn.microsoft.com/en-us/dotnet/api/system.threading.tasks.taskcreationoptions?view=net-7.0
);
task.Start();
var exitCode = task.GetAwaiter().GetResult();
/*Or this.*/
//var exitCode = MainAsync(args, cts.Token).GetAwaiter().GetResult();
return exitCode;// MainAsync(args, cts.Token).GetAwaiter().GetResult();
}
catch (OperationCanceledException ex)
{
Console.WriteLine(ex);
return 1223; // Cancelled.
}
catch(Exception ex)
{
Console.WriteLine(ex);
return -1;
}
}
private static async Task<int> MainAsync(string[] args, CancellationToken cancellationToken)
{
await Something()
return;
}
In the following example I wrote. You can play with maxDegreeOfParallelism & numberOfIteration to understand / see how the task are handle. Good statring point for learning TPL!
private static async Task<int> MainAsync(string[] args, CancellationToken cancellationToken)
{
var infos = new ConcurrentBag<Info>();
var mySuperUselessService = new BigWorkload();
int numberOfSecond = 1;
int numberOfIteration = 25; //Experiment with this
int maxDegreeOfParallelism = 4; //Experiment with this
var simulateWorkTime = TimeSpan.FromSeconds(numberOfSecond);
var informations = Enumerable.Range(1, numberOfIteration)
.Select(x => new Info() { Index = x });
var count = informations.Count();
var chunkNeeded = Math.Round(count / Convert.ToDecimal(maxDegreeOfParallelism), MidpointRounding.ToPositiveInfinity);
var splashInfo = #$"
Press CTRL + C to cancel.
Processing {count} items, maxDegreeOfParallelism set to {maxDegreeOfParallelism}.
But it will be bound by the core on the machine {Environment.ProcessorCount}.
This operation should take ~{chunkNeeded * (numberOfSecond + 0.01m)}s
And will be starting test in 2s
";
Console.WriteLine(splashInfo);
await Task.Delay(TimeSpan.FromSeconds(2));
var parralelOptions = new ParallelOptions() { MaxDegreeOfParallelism = maxDegreeOfParallelism, CancellationToken = cancellationToken};
var stopwatch = new Stopwatch();
stopwatch.Start();
var forLoopTask = Parallel.ForEachAsync(informations, parralelOptions, async (info, token) =>
{
await mySuperUselessService.Simulate(simulateWorkTime, info);
Console.WriteLine(info);
infos.Add(info);
});
await forLoopTask;
stopwatch.Stop();
foreach (var grouped in infos.GroupBy(x => x.ManagedThreadId))
{
Console.WriteLine($"ThreadId: {grouped.Key}");
foreach (var item in grouped)
{
Console.WriteLine($"\t Index: {item.Index} {item.TaskCurrentId}");
}
}
Console.WriteLine($"NumberOfThread: {infos.GroupBy(x => x.ManagedThreadId).Count()}");
Console.WriteLine($"Elasped: {stopwatch.ElapsedMilliseconds / 1000d}s");
Console.WriteLine(splashInfo);
return 0;
}

async and await are not working

I am trying to learn the async and await features of .NET 4.5 .First of all here's my code
static async void Method()
{
await Task.Run(new Action(DoSomeProcess));
Console.WriteLine("All Methods have been executed");
}
static void DoSomeProcess()
{
System.Threading.Thread.Sleep(3000);
}
static void Main(string[] args)
{
Method();
//Console.WriteLine("Method Started");
Console.ReadKey();
}
This code doesn't give me any results on the console. I cant understand why. I mean aren't tasks suppose be just threads that aren't blocking. However if i uncomment the Console.WriteLine() in the main method everything seems to be working fine.
Can anybody tell me what's going on here ?

With the async/await pattern some things are different as previously with threads.
you shouldn't use System.Threading.Thread.Sleep
because this is still blocking and does not work with async.
Instead use Task.Delay
Consider making all your code async. Only the Main method in your console cannot be async of cause
Avoid async void methods. Basically async void is just meant for event handlers which cannot return something. All other async methods should return Task or Task<T>
Modified your example:
static async Task Method()
{
await DoSomeProcess();
Console.WriteLine("All Methods have been executed");
}
static async Task DoSomeProcess()
{
await Task.Delay(3000);
}
Now change your Main method because this should be the place where you start your task
Task.Run(() => Method()).Wait();
//Console.WriteLine("Method Started");
Console.ReadKey();

There is a small learning curve to learn how to use the async and await keywords correctly..
The problem is that nobody waits whom is waiting, there are some other details such as the SyncronizationContext and Task:
you should check some articles:
http://msdn.microsoft.com/en-us/library/vstudio/hh191443.aspx
To use async and await keywords in Console, you need an extra code:
Can't specify the 'async' modifier on the 'Main' method of a console app or
Await a Async Void method call for unit testing or Unit Test Explorer does not show up Async Unit Tests for metro apps
I usually do this approach:
static void Main(string[] args)
{
Console.WriteLine("HELLO WORLD");
var t1 = Task.Factory.StartNew(new Func<Task>(async () => await Method()))
.Unwrap();
Console.WriteLine("STARTED");
t1.Wait();
Console.WriteLine("COMPLETED");
Console.ReadKey();
}
static async Task Method()
{
// this method is perfectly safe to use async / await keywords
Console.WriteLine("BEFORE DELAY");
await Task.Delay(1000);
Console.WriteLine("AFTER DELAY");
}

Can't specify the 'async' modifier on the 'Main' method of a console app

I am new to asynchronous programming with the async modifier. I am trying to figure out how to make sure that my Main method of a console application actually runs asynchronously.
class Program
{
static void Main(string[] args)
{
Bootstrapper bs = new Bootstrapper();
var list = bs.GetList();
}
}
public class Bootstrapper {
public async Task<List<TvChannel>> GetList()
{
GetPrograms pro = new GetPrograms();
return await pro.DownloadTvChannels();
}
}
I know this is not running asynchronously from "the top." Since it is not possible to specify the async modifier on the Main method, how can I run code within main asynchronously?

As you discovered, in VS11 the compiler will disallow an async Main method. This was allowed (but never recommended) in VS2010 with the Async CTP.
Update, 2017-11-30: As of Visual Studio 2017 Update 3 (15.3), the language now supports an async Main - as long as it returns Task or Task<T>. So you can now do this:
class Program
{
static async Task Main(string[] args)
{
Bootstrapper bs = new Bootstrapper();
var list = await bs.GetList();
}
}
The semantics appear to be the same as the GetAwaiter().GetResult() style of blocking the main thread. However, there's no language spec for C# 7.1 yet, so this is only an assumption.
I have recent blog posts about async/await and asynchronous console programs in particular. Here's some background info from the intro post:
If "await" sees that the awaitable has not completed, then it acts asynchronously. It tells the awaitable to run the remainder of the method when it completes, and then returns from the async method. Await will also capture the current context when it passes the remainder of the method to the awaitable.
Later on, when the awaitable completes, it will execute the remainder of the async method (within the captured context).
Here's why this is a problem in Console programs with an async Main:
Remember from our intro post that an async method will return to its caller before it is complete. This works perfectly in UI applications (the method just returns to the UI event loop) and ASP.NET applications (the method returns off the thread but keeps the request alive). It doesn't work out so well for Console programs: Main returns to the OS - so your program exits.
One solution is to provide your own context - a "main loop" for your console program that is async-compatible.
If you have a machine with the Async CTP, you can use GeneralThreadAffineContext from My Documents\Microsoft Visual Studio Async CTP\Samples(C# Testing) Unit Testing\AsyncTestUtilities. Alternatively, you can use AsyncContext from my Nito.AsyncEx NuGet package.
Here's an example using AsyncContext; GeneralThreadAffineContext has almost identical usage:
using Nito.AsyncEx;
class Program
{
static void Main(string[] args)
{
AsyncContext.Run(() => MainAsync(args));
}
static async void MainAsync(string[] args)
{
Bootstrapper bs = new Bootstrapper();
var list = await bs.GetList();
}
}
Alternatively, you can just block the main Console thread until your asynchronous work has completed:
class Program
{
static void Main(string[] args)
{
MainAsync(args).GetAwaiter().GetResult();
}
static async Task MainAsync(string[] args)
{
Bootstrapper bs = new Bootstrapper();
var list = await bs.GetList();
}
}
Note the use of GetAwaiter().GetResult(); this avoids the AggregateException wrapping that happens if you use Wait() or Result.

You can solve this with this simple construct:
class Program
{
static void Main(string[] args)
{
Task.Run(async () =>
{
// Do any async anything you need here without worry
}).GetAwaiter().GetResult();
}
}
That will put everything you do out on the ThreadPool where you'd want it (so other Tasks you start/await don't attempt to rejoin a Thread they shouldn't), and wait until everything's done before closing the Console app. No need for special loops or outside libs.
Edit: Incorporate Andrew's solution for uncaught Exceptions.

You can do this without needing external libraries also by doing the following:
class Program
{
static void Main(string[] args)
{
Bootstrapper bs = new Bootstrapper();
var getListTask = bs.GetList(); // returns the Task<List<TvChannel>>
Task.WaitAll(getListTask); // block while the task completes
var list = getListTask.Result;
}
}

In C# 7.1 you will be able to do a proper async Main. The appropriate signatures for Main method has been extended to:
public static Task Main();
public static Task<int> Main();
public static Task Main(string[] args);
public static Task<int> Main(string[] args);
For e.g. you could be doing:
static async Task Main(string[] args)
{
Bootstrapper bs = new Bootstrapper();
var list = await bs.GetList();
}
At compile time, the async entry point method will be translated to call GetAwaitor().GetResult().
Details: https://blogs.msdn.microsoft.com/mazhou/2017/05/30/c-7-series-part-2-async-main
EDIT:
To enable C# 7.1 language features, you need to right-click on the project and click "Properties" then go to the "Build" tab. There, click the advanced button at the bottom:
From the language version drop-down menu, select "7.1" (or any higher value):
The default is "latest major version" which would evaluate (at the time of this writing) to C# 7.0, which does not support async main in console apps.

I'll add an important feature that all of the other answers have overlooked: cancellation.
One of the big things in TPL is cancellation support, and console apps have a method of cancellation built in (CTRL+C). It's very simple to bind them together. This is how I structure all of my async console apps:
static void Main(string[] args)
{
CancellationTokenSource cts = new CancellationTokenSource();
System.Console.CancelKeyPress += (s, e) =>
{
e.Cancel = true;
cts.Cancel();
};
MainAsync(args, cts.Token).GetAwaiter.GetResult();
}
static async Task MainAsync(string[] args, CancellationToken token)
{
...
}

C# 7.1 (using vs 2017 update 3) introduces async main
You can write:
static async Task Main(string[] args)
{
await ...
}
For more details C# 7 Series, Part 2: Async Main
Update:
You may get a compilation error:
Program does not contain a static 'Main' method suitable for an entry point
This error is due to that vs2017.3 is configured by default as c#7.0 not c#7.1.
You should explicitly modify the setting of your project to set c#7.1 features.
You can set c#7.1 by two methods:
Method 1: Using the project settings window:
Open the settings of your project
Select the Build tab
Click the Advanced button
Select the version you want
As shown in the following figure:
Method2: Modify PropertyGroup of .csproj manually
Add this property:
<LangVersion>7.1</LangVersion>
example:
<PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
<PlatformTarget>AnyCPU</PlatformTarget>
<DebugSymbols>true</DebugSymbols>
<DebugType>full</DebugType>
<Optimize>false</Optimize>
<OutputPath>bin\Debug\</OutputPath>
<DefineConstants>DEBUG;TRACE</DefineConstants>
<ErrorReport>prompt</ErrorReport>
<WarningLevel>4</WarningLevel>
<Prefer32Bit>false</Prefer32Bit>
<LangVersion>7.1</LangVersion>
</PropertyGroup>

If you're using C# 7.1 or later, go with the nawfal's answer and just change the return type of your Main method to Task or Task<int>. If you are not:
Have an async Task MainAsync like Johan said.
Call its .GetAwaiter().GetResult() to catch the underlying exception like do0g said.
Support cancellation like Cory said.
A second CTRL+C should terminate the process immediately. (Thanks binki!)
Handle OperationCancelledException - return an appropriate error code.
The final code looks like:
private static int Main(string[] args)
{
var cts = new CancellationTokenSource();
Console.CancelKeyPress += (s, e) =>
{
e.Cancel = !cts.IsCancellationRequested;
cts.Cancel();
};
try
{
return MainAsync(args, cts.Token).GetAwaiter().GetResult();
}
catch (OperationCanceledException)
{
return 1223; // Cancelled.
}
}
private static async Task<int> MainAsync(string[] args, CancellationToken cancellationToken)
{
// Your code...
return await Task.FromResult(0); // Success.
}

Haven't needed this much yet, but when I've used console application for Quick tests and required async I've just solved it like this:
class Program
{
static void Main(string[] args)
{
MainAsync(args).Wait();
}
static async Task MainAsync(string[] args)
{
// Code here
}
}

For asynchronously calling task from Main, use
Task.Run() for .NET 4.5
Task.Factory.StartNew() for .NET 4.0 (May require Microsoft.Bcl.Async library for async and await keywords)
Details:
http://blogs.msdn.com/b/pfxteam/archive/2011/10/24/10229468.aspx

In Main try changing the call to GetList to:
Task.Run(() => bs.GetList());

When the C# 5 CTP was introduced, you certainly could mark Main with async... although it was generally not a good idea to do so. I believe this was changed by the release of VS 2013 to become an error.
Unless you've started any other foreground threads, your program will exit when Main completes, even if it's started some background work.
What are you really trying to do? Note that your GetList() method really doesn't need to be async at the moment - it's adding an extra layer for no real reason. It's logically equivalent to (but more complicated than):
public Task<List<TvChannel>> GetList()
{
return new GetPrograms().DownloadTvChannels();
}

Newest version of C# - C# 7.1 allows to create async console app. To enable C# 7.1 in project, you have to upgrade your VS to at least 15.3, and change C# version to C# 7.1 or C# latest minor version. To do this, go to Project properties -> Build -> Advanced -> Language version.
After this, following code will work:
internal class Program
{
public static async Task Main(string[] args)
{
(...)
}

As of C# 7.1 the following signatures are valid for the Main method.
public static void Main() { }
public static int Main() { }
public static void Main(string[] args) { }
public static int Main(string[] args) { }
public static async Task Main() { }
public static async Task<int> Main() { }
public static async Task Main(string[] args) { }
public static async Task<int> Main(string[] args) { }
So, now you can do async/await
static async Task Main(string[] args)
{
Console.WriteLine("Hello Asyn Main method!");
await Task.Delay(200);
}

On MSDN, the documentation for Task.Run Method (Action) provides this example which shows how to run a method asynchronously from main:
using System;
using System.Threading;
using System.Threading.Tasks;
public class Example
{
public static void Main()
{
ShowThreadInfo("Application");
var t = Task.Run(() => ShowThreadInfo("Task") );
t.Wait();
}
static void ShowThreadInfo(String s)
{
Console.WriteLine("{0} Thread ID: {1}",
s, Thread.CurrentThread.ManagedThreadId);
}
}
// The example displays the following output:
// Application thread ID: 1
// Task thread ID: 3
Note this statement that follows the example:
The examples show that the asynchronous task executes on a different
thread than the main application thread.
So, if instead you want the task to run on the main application thread, see the answer by #StephenCleary.
And regarding the thread on which the task runs, also note Stephen's comment on his answer:
You can use a simple Wait or Result, and there's nothing wrong
with that. But be aware that there are two important differences: 1)
all async continuations run on the thread pool rather than the main
thread, and 2) any exceptions are wrapped in an AggregateException.
(See Exception Handling (Task Parallel Library) for how to incorporate exception handling to deal with an AggregateException.)
Finally, on MSDN from the documentation for Task.Delay Method (TimeSpan), this example shows how to run an asynchronous task that returns a value:
using System;
using System.Threading.Tasks;
public class Example
{
public static void Main()
{
var t = Task.Run(async delegate
{
await Task.Delay(TimeSpan.FromSeconds(1.5));
return 42;
});
t.Wait();
Console.WriteLine("Task t Status: {0}, Result: {1}",
t.Status, t.Result);
}
}
// The example displays the following output:
// Task t Status: RanToCompletion, Result: 42
Note that instead of passing a delegate to Task.Run, you can instead pass a lambda function like this:
var t = Task.Run(async () =>
{
await Task.Delay(TimeSpan.FromSeconds(1.5));
return 42;
});

In my case I had a list of jobs that I wanted to run in async from my main method, have been using this in production for quite sometime and works fine.
static void Main(string[] args)
{
Task.Run(async () => { await Task.WhenAll(jobslist.Select(nl => RunMulti(nl))); }).GetAwaiter().GetResult();
}
private static async Task RunMulti(List<string> joblist)
{
await ...
}

To avoid freezing when you call a function somewhere down the call stack that tries to re-join the current thread (which is stuck in a Wait), you need to do the following:
class Program
{
static void Main(string[] args)
{
Bootstrapper bs = new Bootstrapper();
List<TvChannel> list = Task.Run((Func<Task<List<TvChannel>>>)bs.GetList).Result;
}
}
(the cast is only required to resolve ambiguity)

class Program
{
public static EventHandler AsyncHandler;
static void Main(string[] args)
{
AsyncHandler+= async (sender, eventArgs) => { await AsyncMain(); };
AsyncHandler?.Invoke(null, null);
}
private async Task AsyncMain()
{
//Your Async Code
}
}

This is hypothetical but I am thinking:
static void Main(string[] args)
{
var context = new Thread(() => /*do stuff*/);
context.Start();
context.Join();
}

Not sure if this is what you're looking for, but I wanted to await a method on load. I ended up using the Main_Shown handler and making it async:
private async void Main_Shown(object sender, EventArgs e)
{
await myAsyncMethod();
}

The following code can be used to make a main async. I've tweak it to use long running tasks (learn more here: https://learn.microsoft.com/en-us/dotnet/api/system.threading.tasks.taskcreationoptions?view=net-7.0)
It's also implementing the cancellation token from the above response.
private static int Main(string[] args)
{
var cts = new CancellationTokenSource();
Console.CancelKeyPress += (s, e) =>
{
e.Cancel = !cts.IsCancellationRequested;
cts.Cancel();
Console.WriteLine("CancellationRequested");
};
try
{
var task = new Task<int>(
() => MainAsync(args, cts.Token).GetAwaiter().GetResult(),
cts.Token,
TaskCreationOptions.LongRunning //https://learn.microsoft.com/en-us/dotnet/api/system.threading.tasks.taskcreationoptions?view=net-7.0
);
task.Start();
var exitCode = task.GetAwaiter().GetResult();
/*Or this.*/
//var exitCode = MainAsync(args, cts.Token).GetAwaiter().GetResult();
return exitCode;// MainAsync(args, cts.Token).GetAwaiter().GetResult();
}
catch (OperationCanceledException ex)
{
Console.WriteLine(ex);
return 1223; // Cancelled.
}
catch(Exception ex)
{
Console.WriteLine(ex);
return -1;
}
}
private static async Task<int> MainAsync(string[] args, CancellationToken cancellationToken)
{
await Something()
return;
}
In the following example I wrote. You can play with maxDegreeOfParallelism & numberOfIteration to understand / see how the task are handle. Good statring point for learning TPL!
private static async Task<int> MainAsync(string[] args, CancellationToken cancellationToken)
{
var infos = new ConcurrentBag<Info>();
var mySuperUselessService = new BigWorkload();
int numberOfSecond = 1;
int numberOfIteration = 25; //Experiment with this
int maxDegreeOfParallelism = 4; //Experiment with this
var simulateWorkTime = TimeSpan.FromSeconds(numberOfSecond);
var informations = Enumerable.Range(1, numberOfIteration)
.Select(x => new Info() { Index = x });
var count = informations.Count();
var chunkNeeded = Math.Round(count / Convert.ToDecimal(maxDegreeOfParallelism), MidpointRounding.ToPositiveInfinity);
var splashInfo = #$"
Press CTRL + C to cancel.
Processing {count} items, maxDegreeOfParallelism set to {maxDegreeOfParallelism}.
But it will be bound by the core on the machine {Environment.ProcessorCount}.
This operation should take ~{chunkNeeded * (numberOfSecond + 0.01m)}s
And will be starting test in 2s
";
Console.WriteLine(splashInfo);
await Task.Delay(TimeSpan.FromSeconds(2));
var parralelOptions = new ParallelOptions() { MaxDegreeOfParallelism = maxDegreeOfParallelism, CancellationToken = cancellationToken};
var stopwatch = new Stopwatch();
stopwatch.Start();
var forLoopTask = Parallel.ForEachAsync(informations, parralelOptions, async (info, token) =>
{
await mySuperUselessService.Simulate(simulateWorkTime, info);
Console.WriteLine(info);
infos.Add(info);
});
await forLoopTask;
stopwatch.Stop();
foreach (var grouped in infos.GroupBy(x => x.ManagedThreadId))
{
Console.WriteLine($"ThreadId: {grouped.Key}");
foreach (var item in grouped)
{
Console.WriteLine($"\t Index: {item.Index} {item.TaskCurrentId}");
}
}
Console.WriteLine($"NumberOfThread: {infos.GroupBy(x => x.ManagedThreadId).Count()}");
Console.WriteLine($"Elasped: {stopwatch.ElapsedMilliseconds / 1000d}s");
Console.WriteLine(splashInfo);
return 0;
}

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C# (C-Sharp) is a programming language developed by Microsoft that runs on the .NET Framework.

async Main wouldn't compile [duplicate] - c#

Wrap your async code in MainAsync() - which is an async function then call MainAsync().GetAwaiter().GetResult();

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