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POHow to ensure message reception order in MassTransit
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  1. POHow to ensure message reception order in MassTransit
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    copied!<p>I have a saga that has 3 states; Initial, ReceivingRows, Completed -</p> <pre><code> public static State Initial { get; set; } public static State ReceivingRows { get; set; } public static State Completed { get; set; } </code></pre> <p>It transitions from Initial to ReceivingRows when it gets a BofMessage (where Bof = Beginning of file). After the BofMessage, it receives a large number of RowMessages where each describes a row in a flat file. Once all RowMessages are sent, an EofMessage is sent and the state changes to Completed. Observe -</p> <pre><code> static void DefineSagaBehavior() { Initially(When(ReceivedBof) .Then((saga, message) =&gt; saga.BeginFile(message)) .TransitionTo(ReceivingRows)); During(ReceivingRows, When(ReceivedRow) .Then((saga, message) =&gt; saga.AddRow(message))); During(ReceivingRows, When(ReceivedRowError) .Then((saga, message) =&gt; saga.RowError(message))); During(ReceivingRows, When(ReceivedEof) .Then((saga, message) =&gt; saga.EndFile(message)) .TransitionTo(Completed)); } </code></pre> <p>This works, except sometimes several RowMessages are received <em>before</em> the BofMessage! This is regardless of the order that I sent them. This means that the messages will be received and ultimately counted as errors, causing them to be missing from the database or file that I finally write them out to.</p> <p>As a temporary fix, I add a little sleep timer hack in this method that does all the publishing –</p> <pre><code> public static void Publish( [NotNull] IServiceBus serviceBus, [NotNull] string publisherName, Guid correlationId, [NotNull] Tuple&lt;string, string&gt; inputFileDescriptor, [NotNull] string outputFileName) { // attempt to load offsets var offsetsResult = OffsetParser.Parse(inputFileDescriptor.Item1); if (offsetsResult.Result != ParseOffsetsResult.Success) { // publish an offsets invalid message serviceBus.Publish&lt;TErrorMessage&gt;(CombGuid.Generate(), publisherName, inputFileDescriptor.Item2); return; } // publish beginning of file var fullInputFilePath = Path.GetFullPath(inputFileDescriptor.Item2); serviceBus.Publish&lt;TBofMessage&gt;(correlationId, publisherName, fullInputFilePath); // HACK: make sure bof message happens before row messages, or else some row messages won't be received Thread.Sleep(5000); // publish rows from feed var feedResult = FeedParser.Parse(inputFileDescriptor.Item2, offsetsResult.Offsets); foreach (var row in feedResult) { // publish row message, unaligned if applicable if (row.Result != ParseRowResult.Success) serviceBus.Publish&lt;TRowErrorMessage&gt;(correlationId, publisherName, row.Fields); else serviceBus.Publish&lt;TRowMessage&gt;(correlationId, publisherName, row.Fields); } // publish end of file serviceBus.Publish&lt;TEofMessage&gt;(correlationId, publisherName, outputFileName); } </code></pre> <p>It’s a 5 second sleep-timer, and is quite an ugly hack. Can anyone inform me why I’m not getting the messages in the order I send them? Can I ensure that these message get sent in the right order if they are unordered by default?</p> <p>Thank you!</p> <p><strong>Please note this is cross-posted from <a href="http://groups.google.com/group/masstransit-discuss/browse_thread/thread/7bd9518a690db4bb" rel="nofollow">http://groups.google.com/group/masstransit-discuss/browse_thread/thread/7bd9518a690db4bb</a> for expedience.</strong></p>
 

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