C# ConcurrentQueue is a thread-safe first in-first out (FIFO) collection. The following example shows how to use a ConcurrentQueue to enqueue and dequeue items.

using System;
using System.Collections.Concurrent;
using System.Threading;
using System.Threading.Tasks;

class EnqueueDequeuePeek
{
    // Demonstrates:
    // ConcurrentQueue<T>.Enqueue()
    // ConcurrentQueue<T>.TryPeek()
    // ConcurrentQueue<T>.TryDequeue()
    static void Main()
    {
        //
        // Construct a ConcurrentQueue
        ConcurrentQueue<int> cq = new ConcurrentQueue<int>();

        //
        // Populate the queue.
        for (int i = 0; i < 10000; i++)
        {
            cq.Enqueue(i);
        }

        //
        // Peek at the first element
        int result;
        if (!cq.TryPeek(out result))
        {
            System.Console.WriteLine(
                "CQ: TryPeek failed when it should have succeeded");
        }
        else if (result != 0)
        {
            System.Console.WriteLine(
                "CQ: Expected TryPeek result of 0, got {0}", result);
        }

        //
        // An action to consume the ConcurrentQueue
        int outerSum = 0;
        Action action = () =>
        {
            int localSum = 0;
            int localValue;
            while (cq.TryDequeue(out localValue))
            {
                localSum += localValue;
            }
            Interlocked.Add(ref outerSum, localSum);
        };

        //
        // Start 4 concurrent consuming actions
        Parallel.Invoke(action, action, action, action);

        System.Console.WriteLine(
            "outerSum = {0}, should be 49995000", outerSum);
    }
}