HttpClient Tasks: Why Am I Getting 'A task was cancelled' Errors?

HttpClient: Understanding "A task was cancelled" Errors

When executing multiple HttpClient tasks, it's essential to address unexpected "A task was cancelled" errors. This article dives into potential causes and provides solutions to mitigate this issue.

Causes of "A task was cancelled" Errors

Typically, a TaskCanceledException is thrown due to one of two reasons:

• Explicit Cancellation: The CancellationTokenSource associated with the task's cancellation token was canceled using Cancel() before the task completed.
• Timeout: The task didn't complete within the specified HttpClient.Timeout duration.

Addressing Timeouts

If explicit cancellation is unlikely, then a timeout is the probable cause. To confirm this:

try
{
    var response = task.Result;
}
catch (TaskCanceledException ex)
{
    if (!ex.CancellationToken.IsCancellationRequested)
    {
        // Likely a timeout
    }
}

Sample Code Snippet

The provided code snippet shows how tasks are added to a list and then executed in parallel using Task.WaitAll(). The HttpClientSendAsync method creates an HttpRequestMessage and sends it via an HttpClient with a specified timeout.

Resolution

To resolve timeouts, consider increasing the HttpClient.Timeout duration or implementing a retry mechanism to handle transient exceptions.

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