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POSync two BackgroundWorkers
 

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  1. POSync two BackgroundWorkers
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    <p>I'm writing a C# wrapper, to a hardware controller using its <a href="http://en.wikipedia.org/wiki/Modbus" rel="nofollow">Modbus</a> protocol.<br> The controller has 12 inputs and 12 outputs.</p> <p>The wrapper has two tasks:<br> 1. Polling the controller's inputs at a constant interval (i.e. 50ms).<br> 2. Running preconfigured sequences, which changes the controller's outputs.</p> <p>The sequence is XML based: </p> <pre><code>&lt;opcode&gt; &lt;register&gt;0&lt;/register&gt; &lt;bit&gt;1&lt;/bit&gt; &lt;duration&gt;500&lt;/duration&gt; &lt;/opcode&gt; &lt;opcode&gt; &lt;register&gt;0&lt;/register&gt; &lt;bit&gt;0&lt;/bit&gt; &lt;duration&gt;0&lt;/duration&gt; &lt;/opcode&gt; .... </code></pre> <p>In the above sample, the controller should turn output #0 On and after 500ms turns it Off.<br> The pauses between operations was achieved using <code>Thread.Sleep()</code>.<br> In the past I've used just one BackgroundWorker. When not running the sequence it did the polling.</p> <p><strong>The challenge:</strong><br> The new demand for the wrapper is that it could detect changes in the controller's inputs while running a sequence.<br> I've modified the wrapper to have 2 backgroundworkers, one for polling and the other for setting the output registers.<br> Each of the BackgroundWorkers calls a seperate function on the controller, they do not try to access each other data nor they share any data.</p> <p><strong>Current code:</strong></p> <pre><code>private void workerSequence_DoWork(object sender, DoWorkEventArgs e) { if (!terminating) if (e.Argument != null) DoSequence(e); } private void workerPoll_DoWork(object sender, DoWorkEventArgs e) { if (!terminating) { DoPoll(); Thread.Sleep(pollInterval); } } private void DoSequence(DoWorkEventArgs e) { string sequenceName = e.Argument.ToString(); foreach (configurationSequencesSequenceOpcode opcode in sequencesList[sequenceName]) { if (workerSequence.CancellationPending) break; byte register = opcode.register; bool bit = opcode.bit; int duration = opcode.duration; SetRegister(register, bit, false); Thread.Sleep(duration); } e.Result = e.Argument; } </code></pre> <p><strong>The problem:</strong><br> It's seems like the two BackgroundWorkers interfere with each other. I've tried using <code>Semaphore</code>, <code>Monitor.Wait()</code> and <code>ManualResetEvent.WaitOne()</code> but the BackgroundWorker, which deals with the sequences, doesn't handles them well. The main issue - its sleep duration is not consistent as before.</p> <p>Any advice will be welcome.</p>
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    1. COI would try to solve this in one thread with a state machine. E.g. create a big loop, which runs forever and inside do, what you need to do currently based on the state. Send a sequence, check output etc.
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      1. USVladimir Perevalov
    2. COHow do they "interfere with each other", and why do you need synchronization?
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      1. USNicholas Butler
    3. COWhen using just one thread, I'm unable to poll the inputs register, as the `Thread.Sleep()` function locks it. I've added some code above.
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