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    <p>Consider this example:</p> <pre><code>public class EnterExitExample { private object myLock; private bool running; private void ThreadProc1() { while (running) { lock (myLock) { // Do stuff here... } Thread.Yield(); } } private void ThreadProc2() { while (running) { lock (myLock) { // Do other stuff here... } Thread.Yield(); } } } </code></pre> <p>Now you have two threads, each waiting for lock, then doing their stuff, then releasing the lock. The <code>lock (myLock)</code> syntax is just sugar for <code>Monitor.Enter(myLock)</code> and <code>Monitor.Exit(myLock)</code>.</p> <p>Let us now look at a more complicated example, where <code>Wait</code> and <code>Pulse</code> come into play.</p> <pre><code>public class PulseWaitExample { private Queue&lt;object&gt; queue; private bool running; private void ProducerThreadProc() { while (running) { object produced = ...; // Do production stuff here. lock (queue) { queue.Enqueue(produced); Monitor.Pulse(queue); } } } private void ConsumerThreadProc() { while (running) { object toBeConsumed; lock (queue) { Monitor.Wait(queue); toBeConsumed = queue.Dequeue(); } // Do consuming stuff with toBeConsumed here. } } } </code></pre> <p>What do we have here? </p> <p>The producer produces an object whenever he feels like it. As soon as he has, he obtains lock on the queue, enqueues the object, then does a <code>Pulse</code> call.</p> <p>At the same time, the consumer does NOT have lock, he left it by calling <code>Wait</code>. As soon as he gets a <code>Pulse</code> on that object, he will re-lock, and do his consuming stuff.</p> <p>So what you have here is a direct thread-to-thread notification that there is something to do for the consumer. If you wouldn't have that, all you could do is have the consumer keep polling on the collection if there is something to do yet. Using <code>Wait</code>, you can make sure that there is.</p>
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    1. POMonitor.Enter vs Monitor.Wait
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    1. USJan Doerrenhaus
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    1. COFrom the other prospective answer "You can only call Monitor.Wait(Object), when you already own the lock". Can the consumer call Monitor.Wait(queue) when Producer has the lock?
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      1. USAdam A
    2. COThe producer has the lock for a short time, the time it takes for a `Queue.Enqueue` and a `Monitor.Pulse` call, the latter dropping the lock. The consumer is either completely outside the lock block, which means he would just acquire the lock, call `Wait`, immediately stop waiting due to the lingering `Pulse`, or he is inside the `Wait` call, making him reacquire lock and do his consuming stuff.
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      1. USJan Doerrenhaus
    3. COAccording to the documentation on [Monitor.Pulse()](http://msdn.microsoft.com/en-us/library/system.threading.monitor.pulse.aspx) that looks like a deadlock waiting to happen: "The Monitor class does not maintain state indicating that the Pulse method has been called. Thus, if you call Pulse when no threads are waiting, the next thread that calls Wait blocks as if Pulse had never been called. If two threads are using Pulse and Wait to interact, this could result in a deadlock. Contrast this with the behavior of the AutoResetEvent class[...]"
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      1. USCristi Diaconescu
 

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