Don't trust server status unless the same value is observed across 3 consecutive polling intervals

Author: sharwell

src/corelib/Providers/Rackspace/CloudServersProvider.cs

@@ -329,9 +329,19 @@ public Server WaitForServerState(string serverId, ServerState[] expectedStates,
 
             var serverDetails = GetDetails(serverId, region, identity);
 
+            /*
+             * The polling implementation uses triple-checked polling to work around a known bug in Cloud
+             * Servers status reporting. Occasionally, for a brief period of time during an asynchronous
+             * server operation, the service will return incorrect values in all of the status fields.
+             * Polling multiple times allows this SDK to provide reliable wait operations even when the
+             * server returns unreliable values.
+             */
+
+            Func<bool> exitCondition = () => serverDetails.TaskState == null && (expectedStates.Contains(serverDetails.Status) || errorStates.Contains(serverDetails.Status));
             int count = 0;
             int currentProgress = -1;
-            while ((serverDetails.TaskState != null || (!expectedStates.Contains(serverDetails.Status) && !errorStates.Contains(serverDetails.Status))) && count < refreshCount)
+            int exitCount = exitCondition() ? 1 : 0;
+            while (exitCount < 3 && count < refreshCount)
             {
                 if (progressUpdatedCallback != null)
                 {
@@ -345,6 +355,10 @@ public Server WaitForServerState(string serverId, ServerState[] expectedStates,
                 Thread.Sleep(refreshDelay ?? TimeSpan.FromMilliseconds(2400));
                 serverDetails = GetDetails(serverId, region, identity);
                 count++;
+                if (exitCondition())
+                    exitCount++;
+                else
+                    exitCount = 0;
             }
 
             if (errorStates.Contains(serverDetails.Status))