Add synchronization to PiscalQueueManager

Web/Services/PiscalQueueManager.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Linq;
+using System.Threading;
 using LeafWeb.Core.DAL;
 using LeafWeb.Core.Entities;
 using LeafWeb.Core.Remote;
@@ -20,10 +21,52 @@ namespace LeafWeb.Web.Services
 
 		public PiscalQueueManager() : this(new DataService(), new PiscalService()) {}
 
+		private static readonly object Lock = new object();
+
 		public void ProcessQueue()
 		{
 			var logger = LogManager.GetCurrentClassLogger();
 
+			if (Monitor.TryEnter(Lock))
+			{
+				logger.Trace("Process entered");
+
+				ProcessRunning(logger);
+
+				ProcessQueue(logger);
+
+				logger.Trace("Process completed");
+
+				Monitor.Exit(Lock);
+			}
+			else
+			{
+				logger.Trace("Process locked, queue already processing");
+			}
+		}
+
+		private void ProcessQueue(ILogger logger)
+		{
+			var runningLeafInputFiles = _dataService.GetLeafInputFiles(LeafInputStatusType.Running).ToList();
+			if (runningLeafInputFiles.Any())
+				return;
+
+			var queuedFile =
+				_dataService
+					.GetLeafInputFiles(LeafInputStatusType.Queued)
+					.OrderBy(l => l.Id)
+					.FirstOrDefault();
+
+			if (queuedFile == null)
+				return;
+
+			logger.Info("LeafInputFile: {0}, Start", queuedFile.Id);
+			_piscalService.RunLeafInputFile(queuedFile);
+			_dataService.SetLeafInputFileStatus(queuedFile, LeafInputStatusType.Running);
+		}
+
+		private void ProcessRunning(ILogger logger)
+		{
 			var runningLeafInputFiles = _dataService.GetLeafInputFiles(LeafInputStatusType.Running).ToList();
 			foreach (var file in runningLeafInputFiles)
 			{
@@ -42,7 +85,8 @@ namespace LeafWeb.Web.Services
 						{
 							_dataService.AddLeafOutputFile(outputFile);
 						}
-						logger.Info("LeafInputFile: {0}, output files: {1}", file.Id, string.Join(", ", leafOutputFiles.Select(o => o.Filename)));
+						logger.Info("LeafInputFile: {0}, output files: {1}", file.Id,
+							string.Join(", ", leafOutputFiles.Select(o => o.Filename)));
 						_dataService.SetLeafInputFileStatus(file, LeafInputStatusType.Complete);
 						break;
 					case PiscalStatus.Error:
@@ -51,23 +95,6 @@ namespace LeafWeb.Web.Services
 						break;
 				}
 			}
-
-			runningLeafInputFiles = _dataService.GetLeafInputFiles(LeafInputStatusType.Running).ToList();
-			if (!runningLeafInputFiles.Any())
-			{
-				var queuedFile =
-					_dataService
-						.GetLeafInputFiles(LeafInputStatusType.Queued)
-						.OrderBy(l => l.Id)
-						.FirstOrDefault();
-
-				if (queuedFile != null)
-				{
-					logger.Info("LeafInputFile: {0}, Start", queuedFile.Id);
-					_piscalService.RunLeafInputFile(queuedFile);
-					_dataService.SetLeafInputFileStatus(queuedFile, LeafInputStatusType.Running);
-				}
-			}
 		}
 
 		public void Dispose()