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copied!<p>You are right. Calling <code>WaitOne</code> inside a lock could lead to a deadlock. And the check to see if the list is empty needs to be done inside the lock otherwise there could be a race with another thread trying to remove an item. Now, your code looks suspiciously like the producer-consumer pattern which is usually implemented with a blocking queue. If you are using .NET 4.0 then you can take advantage of the <a href="http://msdn.microsoft.com/en-us/library/dd267312.aspx" rel="nofollow">BlockingCollection</a> class. </p> <p>However, let me go over a couple of ways you can do it youself. The first uses a <code>List</code> and a <code>ManualResetEvent</code> to demonstrate how this could be done using the data structures in your question. Notice the use of a <code>while</code> loop in the <code>Take</code> method.</p> <pre><code>public class BlockingJobsCollection { private List<Job> m_List = new List<Job>(); private ManualResetEvent m_Signal = new ManualResetEvent(false); public void Add(Job item) { lock (m_List) { m_List.Add(item); m_Signal.Set(); } } public Job Take() { while (true) { lock (m_List) { if (m_List.Count > 0) { Job item = m_List.First(); m_List.Remove(item); if (m_List.Count == 0) { m_Signal.Reset(); } return item; } } m_Signal.WaitOne(); } } } </code></pre> <p>But this not how I would do it. I would go with the simplier solution below with uses <code>Monitor.Wait</code> and <code>Monitor.Pulse</code>. <code>Monitor.Wait</code> is useful because it <em>can</em> be called inside a lock. In fact, it is <em>suppose</em> to be done that way.</p> <pre><code>public class BlockingJobsCollection { private Queue<Job> m_Queue = new Queue<Job>(); public void Add(Job item) { lock (m_Queue) { m_Queue.Enqueue(item); Monitor.Pulse(m_Queue); } } public Job Take() { lock (m_Queue) { while (m_Queue.Count == 0) { Monitor.Wait(m_Queue); } return m_Queue.Dequeue(); } } } </code></pre>

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