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    <p>Im interpreting your questions as a request for an implementatation of the IdleNotifier interface specified below. Also you state that ActionOccured() needs to be fast. </p> <pre><code>public delegate void IdleCallback(); public interface IdleNotifier { // Called by threadpool when more than IdleTimeSpanBeforeCallback // has passed since last call on ActionOccured. IdleCallback Callback { set; } TimeSpan IdleTimeSpanBeforeCallback { set; } void ActionOccured(); } </code></pre> <p>I provide an implementation with System.Threading.Timer below. Important points about the implementation:</p> <ul> <li>We accept that the timer can wake up at any time and make sure this is ok.</li> <li>Since we assume the timer wakes relatively seldom we can do expensive work at these times.</li> <li>Since we can do all logic in the timer callback all we need to do to "push the timer" is to remeber when last we pushed it.</li> </ul> <p>Implementation:</p> <pre><code>public class IdleNotifierTimerImplementation : IdleNotifier { private readonly object SyncRoot = new object(); private readonly Timer m_Timer; private IdleCallback m_IdleCallback = null; private TimeSpan m_IdleTimeSpanBeforeEvent = TimeSpan.Zero; // Null means there has been no action since last idle notification. private DateTime? m_LastActionTime = null; public IdleNotifierTimerImplementation() { m_Timer = new Timer(OnTimer); } private void OnTimer(object unusedState) { lock (SyncRoot) { if (m_LastActionTime == null) { m_Timer.Change(m_IdleTimeSpanBeforeEvent, TimeSpan.Zero); return; } TimeSpan timeSinceLastUpdate = DateTime.UtcNow - m_LastActionTime.Value; if (timeSinceLastUpdate &gt; TimeSpan.Zero) { // We are no idle yet. m_Timer.Change(timeSinceLastUpdate, TimeSpan.Zero); return; } m_LastActionTime = null; m_Timer.Change(m_IdleTimeSpanBeforeEvent, TimeSpan.Zero); } if (m_IdleCallback != null) { m_IdleCallback(); } } // IdleNotifier implementation below public void ActionOccured() { lock (SyncRoot) { m_LastActionTime = DateTime.UtcNow; } } public IdleCallback Callback { set { lock (SyncRoot) { m_IdleCallback = value; } } } public TimeSpan IdleTimeSpanBeforeCallback { set { lock (SyncRoot) { m_IdleTimeSpanBeforeEvent = value; // Run OnTimer immediately m_Timer.Change(TimeSpan.Zero, TimeSpan.Zero); } } } } </code></pre> <p>There are many straight-forward performance improvements on this code.</p> <p>If anyone would be intrested in my first thoughts on this just ask me.</p>
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    1. PO"Atomically" changing a System.Threading.Timer
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