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Parallel.ForEach using Thread.Sleep equivalent

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孤独总比滥情好
孤独总比滥情好 2021-01-18 07:40

So here\'s the situation: I need to make a call to a web site that starts a search. This search continues for an unknown amount of time, and the only way I know if the searc

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  • 一个人的身影
    一个人的身影 (楼主)
    2021-01-18 08:06

    You can also write a generic function using TaskCompletionSource and Threading.Timer to return a Task that becomes complete once a specified retry function succeeds.

    public static Task RetryAsync(Func retryFunc, TimeSpan retryInterval)
{
    return RetryAsync(retryFunc, retryInterval, CancellationToken.None);
}

public static Task RetryAsync(Func retryFunc, TimeSpan retryInterval, CancellationToken cancellationToken)
{
    var tcs = new TaskCompletionSource();

    cancellationToken.Register(() => tcs.TrySetCanceled());

    var timer = new Timer((state) =>
    {
        var taskCompletionSource = (TaskCompletionSource) state;

        try
        {                   
            if (retryFunc())
            {
                taskCompletionSource.TrySetResult(null);
            }
        }
        catch (Exception ex)
        {
            taskCompletionSource.TrySetException(ex);
        }
    }, tcs, TimeSpan.FromMilliseconds(0), retryInterval);

    // Once the task is complete, dispose of the timer so it doesn't keep firing. Also captures the timer
    // in a closure so it does not get disposed.
    tcs.Task.ContinueWith(t => timer.Dispose(),
                          CancellationToken.None,
                          TaskContinuationOptions.ExecuteSynchronously,
                          TaskScheduler.Default);

    return tcs.Task;
}



    You can then use RetryAsync like this:
    


    var searchTasks = new List();

searchTasks.AddRange(items.Select(
        downloadItem => RetryAsync( () => isSearchFinished(downloadItem),  TimeSpan.FromSeconds(2))  // retry timout
        .ContinueWith(t => downloadData(downloadItem), 
                      CancellationToken.None, 
                      TaskContinuationOptions.OnlyOnRanToCompletion, 
                      TaskScheduler.Default)));

await Task.WhenAll(searchTasks.ToArray());

    


    The ContinueWith part specifies what you do once the task has completed successfully. In this case it will run your downloadData method on a thread pool thread because we specified TaskScheduler.Default and the continuation will only execute if the task ran to completion, i.e. it was not canceled and no exception was thrown.
    
    
    
             
    
                                                        
    
            
            
    
              
                
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