Add ThreadPool statistics to Timeout message to help debug IOCP starvation issues.

StackExchange.Redis/StackExchange/Redis/ConnectionMultiplexer.cs

@@ -1817,6 +1817,8 @@ internal T ExecuteSyncImpl<T>(Message message, ResultProcessor<T> processor, Ser
                                 .Append(", wr=").Append(wr).Append("/").Append(wq)
                                 .Append(", in=").Append(@in).Append("/").Append(ar);
 
+                            AppendThreadPoolStats(sb);
+
                             errMessage = sb.ToString();
                             if (stormLogThreshold >= 0 && queue >= stormLogThreshold && Interlocked.CompareExchange(ref haveStormLog, 1, 0) == 0)
                             {
@@ -1839,6 +1841,27 @@ internal T ExecuteSyncImpl<T>(Message message, ResultProcessor<T> processor, Ser
             }
         }
 
+        private static void AppendThreadPoolStats(StringBuilder errorMessage)
+        {
+            //BusyThreads =  TP.GetMaxThreads() –TP.GetAVailable();
+            //If BusyThreads >= TP.GetMinThreads(), then threadpool growth throttling is possible.
+
+            int maxIoThreads, maxWorkerThreads;
+            ThreadPool.GetMaxThreads(out maxWorkerThreads, out maxIoThreads);
+
+            int freeIoThreads, freeWorkerThreads;
+            ThreadPool.GetAvailableThreads(out freeWorkerThreads, out freeIoThreads);
+
+            int minIoThreads, minWorkerThreads;
+            ThreadPool.GetMinThreads(out minWorkerThreads, out minIoThreads);
+
+            int busyIoThreads = maxIoThreads - freeIoThreads;
+            int busyWorkerThreads = maxWorkerThreads - freeWorkerThreads;
+
+            errorMessage.AppendFormat(", IOCP:(Busy={0},Min={1},Max={2})", busyIoThreads, minIoThreads, maxIoThreads);
+            errorMessage.AppendFormat(", WORKER:(Busy={0},Min={1},Max={2})", busyWorkerThreads, minWorkerThreads, maxWorkerThreads);
+        }
+
         /// <summary>
         /// Should exceptions include identifiable details? (key names, additional .Data annotations)
         /// </summary>