在ActionBlock中收集结果时阻止收集

Question

I think in the test method the "results" collection variable has to be of type BlockingCollection<int> instead of List<int> . Prove it to me if I am wrong. I have taken this example from https://blog.stephencleary.com/2012/11/async-producerconsumer-queue-using.html

private static async Task Produce(BufferBlock<int> queue, IEnumerable<int> values)
{
    foreach (var value in values)
    {
        await queue.SendAsync(value);
    }
}

public async Task ProduceAll(BufferBlock<int> queue)
{
    var producer1 = Produce(queue, Enumerable.Range(0, 10));
    var producer2 = Produce(queue, Enumerable.Range(10, 10));
    var producer3 = Produce(queue, Enumerable.Range(20, 10));
    await Task.WhenAll(producer1, producer2, producer3);
    queue.Complete();
}

[TestMethod]
public async Task ConsumerReceivesCorrectValues()
{
    var results = new List<int>();

    // Define the mesh.
    var queue = new BufferBlock<int>(new DataflowBlockOptions { BoundedCapacity = 5, });

    //var consumerOptions = new ExecutionDataflowBlockOptions { BoundedCapacity = 1, };

    var consumer = new ActionBlock<int>(x => results.Add(x), consumerOptions);
    queue.LinkTo(consumer, new DataflowLinkOptions { PropagateCompletion = true, });

    // Start the producers.
    var producers = ProduceAll(queue);

    // Wait for everything to complete.
    await Task.WhenAll(producers, consumer.Completion);

    // Ensure the consumer got what the producer sent.
    Assert.IsTrue(results.OrderBy(x => x).SequenceEqual(Enumerable.Range(0, 30)));
}

Answer 1

Since ActionBlock<T> restricts its delegate to one-execution-at-a-time by default ( MaxDegreeOfParallelism of 1 ), it is not necessary to use BlockingCollection<T> instead of List<T> .

The test in your code passes just fine for me, as expected.

If ActionBlock<T> were passed an option with a higher MaxDegreeOfParallelism , then you would need to protect the List<T> or replace it with a BlockingCollection<T> .