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Sequential processing of asynchronous tasks

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旧时难觅i
旧时难觅i 2020-12-08 02:53

Assume the following synchronous code:

try
{
    Foo();
    Bar();
    Fubar();
    Console.WriteLine(\"All done\");
}
catch(Exception e) // For illustration
5条回答
  • 隐瞒了意图╮
    隐瞒了意图╮ (楼主)
    2020-12-08 03:22

    You should be able to create a method to combine two tasks, and only start the second if the first succeeds.

    public static Task Then(this Task parent, Task next)
{
    TaskCompletionSource tcs = new TaskCompletionSource();
    parent.ContinueWith(pt =>
    {
        if (pt.IsFaulted)
        {
            tcs.SetException(pt.Exception.InnerException);
        }
        else
        {
            next.ContinueWith(nt =>
            {
                if (nt.IsFaulted)
                {
                    tcs.SetException(nt.Exception.InnerException);
                }
                else { tcs.SetResult(null); }
            });
            next.Start();
        }
    });
    return tcs.Task;
}



    you can then chain tasks together:
    


    Task outer = FooAsync()
    .Then(BarAsync())
    .Then(FubarAsync());

outer.ContinueWith(t => {
    if(t.IsFaulted) {
        //handle exception
    }
});

    


    If your tasks are started immediately you can just wrap them in a Func:
    


    public static Task Then(this Task parent, Func nextFunc)
{
    TaskCompletionSource tcs = new TaskCompletionSource();
    parent.ContinueWith(pt =>
    {
        if (pt.IsFaulted)
        {
            tcs.SetException(pt.Exception.InnerException);
        }
        else
        {
            Task next = nextFunc();
            next.ContinueWith(nt =>
            {
                if (nt.IsFaulted)
                {
                    tcs.SetException(nt.Exception.InnerException);
                }
                else { tcs.SetResult(null); }
            });
        }
    });
    return tcs.Task;
}

    
    
             
    
                                                        
    
            
            
    
              
                
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