cancel_10.cs

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

    CancellationTokenRegistration externalCancellation = default;
    if (cancellationToken.CanBeCanceled)
    {
        externalCancellation = cancellationToken.UnsafeRegister(static state =>
        {
            ((CancellationTokenSource)state!).Cancel();
        }, timeoutTokenSource);
    }

    var clientLifetimeCancellation = clientLifetimeTokenSource.Token.UnsafeRegister(static state =>
    {
        ((CancellationTokenSource)state!).Cancel();
    }, timeoutTokenSource);

    timeoutTokenSource.CancelAfter(Timeout);

    try
    {
        await SendCoreAsync(timeoutTokenSource.Token);
    }
    catch (OperationCanceledException ex) when (ex.CancellationToken == timeoutTokenSource.Token)
    {
        // exception handling

        if (cancellationToken.IsCancellationRequested)
        {
            throw new OperationCanceledException(ex.Message, ex, cancellationToken);
        }
        else if (clientLifetimeTokenSource.IsCancellationRequested)
        {
            throw new OperationCanceledException("Client is disposed.", ex, clientLifetimeTokenSource.Token);
        }
        else
        {
            throw new TimeoutException($"The request was canceled due to the configured Timeout of {Timeout.TotalSeconds} seconds elapsing.", ex);
        }
    }
    finally
    {
        externalCancellation.Dispose();
        clientLifetimeCancellation.Dispose();
        if (timeoutTokenSource.TryReset())
        {
            timeoutTokenSourcePool.Return(timeoutTokenSource);
        }
    }
}