C# how to start a new "thread" in an async method?

user_788454 0
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I have two async methods, Test1 and Test2.

In Test1, I want to call Test2 "in a new thread".

In other words, I want a separate "thread" to go to execute Test2, and Test1 step over Test2 call and do not wait for it to finish.

private async Task Test2()
{
    // some time-consuming work to do...
}

public async Task Test1()
{
    // How to call Test2 and immediately move on to the next line and let a separate "thread" to
    // execute Test2?
}
async-await c#
1 Answers

Let's assume that Test2 has some CPU-intensive logic and some asynchronous calls:

private async Task Test2()
{
    for (var i = 1; i < 1_000_000; i++)
    {
    }

    await Task.Delay(TimeSpan.FromMinutes(1));

    for (var i = 1; i < 1_000_000; i++)
    {
    }
}

If Test2 is invoked without await, then current thread would execute logic before fist await in Test2 method prior to returning to Test1. Meaning execution will return to Test1 only after the first for loop finishes:

public async Task Test1()
{
    var _ = Test2();
}

If you require Test1 to continue execution immediately after the Test2 invocation, than it has to be scheduled to another thread from ThreadPool, which can be done with Task.Run, for example:

public async Task Test1()
{
    var _ = Task.Run(() => Test2());
}

In this case you don't have the control when Test2 actually gets executed by ThreadPool (it can happen that Test1 exits even before Test2 is started) and the task, returned by Task.Run will complete only when Task2 exits or throws an error. So you can await it or use the task later in your code, or simply ignore it, if your logic is not concerned about the result.

And if you are not going to await the task from Test2 method, it's worthwhile to catch and handle/log possible errors in it directly, otherwise it will fail silently, which might cause hard to investigate issues.

user_21389590
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