.NET BlockingCollection<T> CPU usage

Question

Running this program will chew up 25% CPU power in a four cores system. So basically something is running at full thrust. I narrowed it down to the consumer however the load doesn't stop on pressing "x" which should terminate my consumers.

my code

internal class TestBlockingCollectionConsumerProducer2
{
    private int _itemCount;

    internal void Run()
    {
        BlockingCollection<string> blockingCollection = new BlockingCollection<string>();

        // The token source for issuing the cancelation request.
        CancellationTokenSource cts = new CancellationTokenSource();

        // Simple thread waiting for a Console 'x'
        Task.Factory.StartNew(() =>
        {
            if (Console.ReadKey().KeyChar == 'x')
            {
                cts.Cancel();
            }
        });

        // start producer
        Task.Factory.StartNew(() => Produce(blockingCollection, cts.Token));

        // start multiple consumers
        const int THREAD_COUNT = 5;
        for (int i = 0; i < THREAD_COUNT; i++)
        {
            Task.Factory.StartNew(() => Consume(blockingCollection, cts.Token));
        }

        while (true);
    }

    private void Produce(BlockingCollection<string> blockingCollection, CancellationToken cancellationToken)
    {
        while (true)
        {
            for (int i = 0; i < 10; i++)
            {
                blockingCollection.Add(string.Format("Item {0}", _itemCount++), cancellationToken);
            }

            Console.WriteLine("Added 10 items. Current queue length:" + blockingCollection.Count);
            Thread.Sleep(10000);
        }
    }

    private void Consume(BlockingCollection<string> blockingCollection, CancellationToken cancellationToken)
    {
        try
        {
            foreach (string item in blockingCollection.GetConsumingEnumerable(cancellationToken))
            {
                Console.WriteLine(string.Format("[{0}] Consumer: Consuming: {1}", Thread.CurrentThread.ManagedThreadId, item));
                Thread.Sleep(2500);
            }
        }
        catch (OperationCanceledException)
        {
            Console.WriteLine("[{0}] Consumer: Operation has been canceled.", Thread.CurrentThread.ManagedThreadId);
        }
    }
}

My question is:
1. Why is the CPU load so high? Shouldn't GetConsumingEnumerable() block and therefore use no CPU time at all?
2. Why doesn't it stop on cts.Cancel()?

Answer 1

Problem isn't with the BlockingCollection .

It is the infinite loop with while (true); . What this is doing in Run method? That's what burning your cpu.

I see Produce method doesn't respect the CancellationToken . Instead of infinite loop, you should be using while (!cancellationToken.IsCancellationRequested) .

Also, for cts.Cancel it indeed cancels the operation. If that doesn't works for some reason, please provide small but complete program which reproduces the problem.