How to dequeue when new item in queue

Question

I've an application that works with a queue with strings (which corresponds to different tasks that application needs to perform). At random moments the queue can be filled with strings (like several times a minute sometimes but it also can take a few hours.

Till now I always had a timer that checked every few seconds the queue whether there were items in the queue and removed them.

I think there must be a nicer solution than this way. Is there any way to get an event or so when an item is added to the queue?

Answer 1

Yes. Take a look at TPL Dataflow, in particular, the BufferBlock<T>, which does more or less the same as BlockingCollection without the nasty side-effect of jamming up your threads by leveraging async/await.

So you can:

void Main()
{
    var b = new BufferBlock<string>();
    AddToBlockAsync(b);
    ReadFromBlockAsync(b);
}

public async Task AddToBlockAsync(BufferBlock<string> b)
{
    while (true)
    {
        b.Post("hello");
        await Task.Delay(1000);
    }
}

public async Task ReadFromBlockAsync(BufferBlock<string> b)
{
    await Task.Delay(10000); //let some messages buffer up...
    while(true)
    {
        var msg = await b.ReceiveAsync();
        Console.WriteLine(msg);
    }
}

Answer 2

I'd take a look at BlockingCollection.GetConsumingEnumerable. The collection will be backed with a queue by default, and it is a nice way to automatically take values from the queue as they are added using a simple foreach loop.

There is also an overload that allows you to supply a CancellationToken meaning you can cleanly break out.