Is there a TPL dataflow block that doesn't take input but returns output?

Question

The title of my question says it all.

I am looking for a TPL dataflow block that doesn't need an input.

Right now I am using a transform block but it's input is unused.

Answer 1

I would build a block like this from a BufferBlock<T>: the method accepts a delegate that presents the ITargetBlock<T> side of the block and returns the ISourceBlock<T> side of it. This way, the delegate can send input to the block, but from the outside, it looks like a block that only produces output.

The code:

public static ISourceBlock<T> CreateProducerBlock<T>(
    Func<ITargetBlock<T>, Task> producer,
    int boundedCapacity = DataflowBlockOptions.Unbounded)
{
    var block = new BufferBlock<T>(
        new ExecutionDataflowBlockOptions { BoundedCapacity = boundedCapacity });

    Task.Run(async () =>
    {
        try
        {
            await producer(block);

            block.Complete();
        }
        catch (Exception ex)
        {
            ((IDataflowBlock)block).Fault(ex);
        }
    });

    return block;
}

Example usage:

var producer = CreateProducerBlock<int>(async target =>
{
    await target.SendAsync(10);
    await target.SendAsync(20);
});

ITargetBlock<int> consumer = …;

producer.LinkTo(consumer);