I've been trying for a while to get something I thought would be simple working with .NET 4.5
I want to fire off two long running tasks at same time and collect the
results in in the best C# 4.5 (RTM) way
The following works but I don't like it because:
Sleep
to be an async method so it can await
other methodsTask.Run()
Working code:
public static void Go()
{
Console.WriteLine("Starting");
var task1 = Task.Run(() => Sleep(5000));
var task2 = Task.Run(() => Sleep(3000));
int totalSlept = task1.Result + task2.Result;
Console.WriteLine("Slept for a total of " + totalSlept + " ms");
}
private static int Sleep(int ms)
{
Console.WriteLine("Sleeping for " + ms);
Thread.Sleep(ms);
Console.WriteLine("Sleeping for " + ms + " FINISHED");
return ms;
}
Non working code:
Update: This actually works and is the correct way to do it, the only problem is the Thread.Sleep
This code doesn't work because the call to Sleep(5000)
immediately starts the task running so Sleep(1000)
doesn't run until it has completed. This is true even though Sleep
is async
and I'm not using await
or calling .Result
too soon.
I thought maybe there is a way to get a non-running Task<T>
by calling an async
method so I could then call Start()
on the two tasks, but I can't figure out how to get a Task<T>
from calling an async method.
public static void Go()
{
Console.WriteLine("Starting");
var task1 = Sleep(5000); // blocks
var task2 = Sleep(1000);
int totalSlept = task1.Result + task2.Result;
Console.WriteLine("Slept for " + totalSlept + " ms");
}
private static async Task<int> Sleep(int ms)
{
Console.WriteLine("Sleeping for " + ms);
Thread.Sleep(ms);
return ms;
}
This question is related to
c#
asynchronous
task-parallel-library
.net-4.5
This article helped explain a lot of things. It's in FAQ style.
This part explains why Thread.Sleep
runs on the same original thread - leading to my initial confusion.
Does the “async” keyword cause the invocation of a method to queue to the ThreadPool? To create a new thread? To launch a rocket ship to Mars?
No. No. And no. See the previous questions. The “async” keyword indicates to the compiler that “await” may be used inside of the method, such that the method may suspend at an await point and have its execution resumed asynchronously when the awaited instance completes. This is why the compiler issues a warning if there are no “awaits” inside of a method marked as “async”.
async Task<int> LongTask1() {
...
return 0;
}
async Task<int> LongTask2() {
...
return 1;
}
...
{
Task<int> t1 = LongTask1();
Task<int> t2 = LongTask2();
await Task.WhenAll(t1,t2);
//now we have t1.Result and t2.Result
}
To answer this point:
I want Sleep to be an async method so it can await other methods
you can maybe rewrite the Sleep
function like this:
private static async Task<int> Sleep(int ms)
{
Console.WriteLine("Sleeping for " + ms);
var task = Task.Run(() => Thread.Sleep(ms));
await task;
Console.WriteLine("Sleeping for " + ms + "END");
return ms;
}
static void Main(string[] args)
{
Console.WriteLine("Starting");
var task1 = Sleep(2000);
var task2 = Sleep(1000);
int totalSlept = task1.Result +task2.Result;
Console.WriteLine("Slept for " + totalSlept + " ms");
Console.ReadKey();
}
running this code will output :
Starting
Sleeping for 2000
Sleeping for 1000
*(one second later)*
Sleeping for 1000END
*(one second later)*
Sleeping for 2000END
Slept for 3000 ms
It's weekend now!
public async void Go()
{
Console.WriteLine("Start fosterage...");
var t1 = Sleep(5000, "Kevin");
var t2 = Sleep(3000, "Jerry");
var result = await Task.WhenAll(t1, t2);
Console.WriteLine($"My precious spare time last for only {result.Max()}ms");
Console.WriteLine("Press any key and take same beer...");
Console.ReadKey();
}
private static async Task<int> Sleep(int ms, string name)
{
Console.WriteLine($"{name} going to sleep for {ms}ms :)");
await Task.Delay(ms);
Console.WriteLine("${name} waked up after {ms}ms :(";
return ms;
}
While your Sleep
method is async, Thread.Sleep
is not. The whole idea of async is to reuse a single thread, not to start multiple threads. Because you've blocked using a synchronous call to Thread.Sleep, it's not going to work.
I'm assuming that Thread.Sleep
is a simplification of what you actually want to do. Can your actual implementation be coded as async methods?
If you do need to run multiple synchronous blocking calls, look elsewhere I think!
Source: Stackoverflow.com