How to determine whether Task.Run is completed within a loop

问题

This may be an odd question and it is really for my educational purpose so I can apply it in future scenarios that may come up.

I am using C#.

I am stress testing so this is not quite production code.

I upload data to my server via a web service.

I start the service off using a Run.Task.

I check to see if the Task is completed before allowing the next Run.Task to begin.

This is done within a loop.

However, because I am using a modular declared Task will not the result be affected? I could declare a local Task.Run variable but I want to see how far I can get with this question 1st.

If the Task.Run can raise an event to say it is completed then this may not be an issue?

This is my code:

//module declaration:

private static Task webTask = Task.Run(() => { System.Windows.Forms.Application.DoEvents(); });

//in a function called via a timer

if (webTask.IsCompleted)
{
   //keep count of competed tasks
}


webTask = Task.Run(() =>
{
    try 
    { 
         wcf.UploadMotionDynamicRaw(bytes);  //my web service
    }
    catch (Exception ex)
    {
        //deal with error
    }
);

回答1:

IMO you do not need the timer. Using Task Continuation you subscribe to the done event:

System.Threading.Tasks.Task
.Run(() => 
{
    // simulate processing
    for (var i = 0; i < 10; i++)
    {
        Console.WriteLine("do something {0}", i + 1);
    }
})
.ContinueWith(t => Console.WriteLine("done."));

The output is:

do something 1
do something 2
.
.
do something 9
do something 10
done

Your code could look like this:

var webTask = Task.Run(() =>
{
    try 
    { 
        wcf.UploadMotionDynamicRaw(bytes);  //my web service
    }
    catch (Exception ex)
    {
        //deal with error
    }
}).ContinueWith(t => taskCounter++);

With task continuation you could even differentiate between failed and success process result, if you want to count only successfull tasks - using the TaskContinuationOptrions.

回答2:

You can wait for your task to complete by awaiting your task like this

await webTask;

that will asynchronously wait for 'webTask' to complete. Instead of the timer you can use await Task.Delay which will asynchronously wait for the delay to expire. I would also consider making the wcf call asynchronous so you don't have to call inside Task.Run. See this question for some tips.

I'd rewrite the code as follows:

public async Task UploadAsync()
{
    while(true)
    {
        await Task.Delay(1000); // this is essentially your timer

        // wait for the webTask to complete asynchrnously
        await webTask;

        //keep count of competed tasks

        webTask = Task.Run(() =>
                        {
                            try 
                            { 
                                // consider generating an asynchronous method for this if possible.
                                wcf.UploadMotionDynamicRaw(bytes);  //my web service
                            }
                            catch (Exception ex)
                            {
                                //deal with error
                            }
                        });     
    }
}

来源：https://stackoverflow.com/questions/27764502/how-to-determine-whether-task-run-is-completed-within-a-loop

标签

task