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copied!<blockquote> <p>im just not sure how multiple timers running under a service would interact and how the threading will work when they all need to write to the same xml file.</p> <p>any thoughts on this?</p> </blockquote> <p>It won't work well.</p> <p>Timers are queued to the thread pool. The thread pool will only create a certain number of active threads at a time:</p> <p><a href="http://msdn.microsoft.com/en-us/library/0ka9477y.aspx" rel="nofollow">http://msdn.microsoft.com/en-us/library/0ka9477y.aspx</a></p> <blockquote> <p>The number of operations that can be queued to the thread pool is limited only by available memory; however, the thread pool limits the number of threads that can be active in the process simultaneously</p> </blockquote> <p>In addition, writing to the same file from multiple threads is going to give you bad results.</p> <p>Not to mention it will be much harder to figure out what your application is doing if you have all those threads running.</p> <p><strong>A simpler approach</strong></p> <p>Take an existing timer and build your own timing system upon it that doesn't use threads.</p> <ul> <li>Create a structure defining a countdown entry.</li> </ul> <p>Code:</p> <pre><code>public class Countdown { public DateTime Time { get; set; } public event Action Elapsed { get; set; } public void RaiseElasped() { if(Elapsed != null) Elapsed(); } } </code></pre> <ul> <li><p>Read your file, and create: <code>Dictionary<string, Countdown></code> (name -> countdown). Put the same code in each action that you were going to put in the timers.</p></li> <li><p>Create a <code>FileSystemWatcher</code> to look for changes to your input file. When the file is triggered, modify the dictionary as necessary.</p></li> <li><p>Create a single timer with a resolution of one minute.</p></li> <li><p>Every time that timer is triggered, check each item in the dictionary. If the target time has passed, call <code>RaiseElapsed</code>. (possibly remove it from the dictionary, too?)</p></li> </ul> <p>From this point, it is hard to determine exactly what you'd want to do, because you didn't describe what gets written to a file, when it happens, how often, or what happens once your countdown has elapsed. You should be able to figure out the rest yourself, though.</p> <p>The advantage of this approach is that single-threaded programs are much easier to debug, and you won't get any of the issues your question asked about (concurrent file access, or having too many threads running).</p> <p>The disadvantage is that it might bog down when you have a lot of entries. But if you have a lot of entries, you should really be using a database instead of of files.</p>

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