GitStatusCache: calling ClearCachedStatus() shouldn't wait for running GetStatusSet() calls in the background.

This fixes a performance issue when running "Include In Project" on a folder with many files (when using git).

src/AddIns/VersionControl/GitAddIn/Src/GitStatusCache.cs

@@ -23,6 +23,7 @@ namespace ICSharpCode.GitAddIn
 	
 	public static class GitStatusCache
 	{
+		static object getStatusLock = new object();
 		static List<KeyValuePair<string, GitStatusSet>> statusSetDict = new List<KeyValuePair<string, GitStatusSet>>();
 		
 		public static void ClearCachedStatus(string fileName)
@@ -47,17 +48,24 @@ namespace ICSharpCode.GitAddIn
 		
 		public static GitStatusSet GetStatusSet(string wcRoot)
 		{
-			lock (statusSetDict) {
+			// Prevent multiple GetStatusSet calls from running in parallel
+			lock (getStatusLock) {
 				GitStatusSet statusSet;
+				// Don't hold statusSetDict during the whole operation; we don't want
+				// to slow down other threads calling ClearCachedStatus()
+				lock (statusSetDict) {
 					foreach (var pair in statusSetDict) {
 						if (FileUtility.IsEqualFileName(pair.Key, wcRoot))
 							return pair.Value;
 					}
+				}
 				
 				statusSet = new GitStatusSet();
 				GitGetFiles(wcRoot, statusSet);
 				GitGetStatus(wcRoot, statusSet);
+				lock (statusSetDict) {
 					statusSetDict.Add(new KeyValuePair<string, GitStatusSet>(wcRoot, statusSet));
+				}
 				return statusSet;
 			}
 		}