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POProducer-Consumer with a variation - How to synchronize with thread signal/wait?
 

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    <p>While working on a large project I realized I was making a lot of calls to be scheduled in the future. Since these were fairly light-weight, I thought it might be better to use a separate scheduler.</p> <pre><code>ThreadPool.QueueUserWorkItem (() =&gt; { Thread.Sleep (5000); Foo (); // Call is to be executed after sometime }); </code></pre> <p>So I created a separate scheduler class that runs on its own thread and executes these events. I have 2 functions that access a shared queue from separate threads. I'd use a lock, but since one of the threads needs to sleep-wait, I wasn't sure how to release the lock.</p> <pre><code>class Scheduler { SortedDictionary &lt;DateTime, Action&gt; _queue; EventWaitHandle _sync; // Runs on its own thread void Run () { while (true) { // Calculate time till first event // If queue empty, use pre-defined value TimeSpan timeDiff = _queue.First().Key - DateTime.Now; // Execute action if in the next 100ms if (timeDiff &lt; 100ms) ... // Wait on event handle for time else _sync.WaitOne (timeDiff); } } // Can be called by any thread void ScheduleEvent (Action action, DataTime time) { _queue.Add (time, action); // Signal thread to wake up and check again _sync.Set (); } } </code></pre> <p><li> The trouble is, I'm not sure how to synchronize access to the queue between the 2 functions. I can't use a monitor or mutex, because Run() will sleep-wait, thus causing a deadlock. What is the right synchronization mechanism to use here? (If there a mechanism to atomically start the sleep-wait process and immediately release the lock, that might solve my problem) <li> How can I verify there is no race-condition? <li> Is this a variation of the producer consumer problem, or is there a more relevant synchronization problem-description? <br/><br/> While this is somewhat geared towards C#, I'd be happy to hear a general solution to this. Thanks!</p>
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    1. COYou have two different things: a timer and a queue. The access to the queue should be protected. The consumer should wake up by its timer OR by a message issued by the producer. So one entity is missing in your design ... queue access atomicity and isolation
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    2. CO@belisarius, yes you are right. I wasn't sure how to protect the queue.
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