cancel_08.cs

public async Task SendAsync(CancellationToken cancellationToken = default)
{
    var timeoutTokenSource = timeoutTokenSourcePool.Get();

    CancellationTokenRegistration externalCancellation = default;
    if (cancellationToken.CanBeCanceled)
    {
        // When raised argument CancellationToken, raise Timeout's CancellationToken
        externalCancellation = cancellationToken.UnsafeRegister(static state =>
        {
            ((CancellationTokenSource)state!).Cancel();
        }, timeoutTokenSource);
    }

    timeoutTokenSource.CancelAfter(Timeout);

    try
    {
        await SendCoreAsync(timeoutTokenSource.Token);
    }
    finally
    {
        // Unregister(must before `TryReset`),
        // CancellationTokenRegistration.Dispose block and wait reliably until the release is completed (or the execution is finished if a callback is being executed)
        externalCancellation.Dispose();
        if (timeoutTokenSource.TryReset())
        {
            timeoutTokenSourcePool.Return(timeoutTokenSource);
        }
    }
}