Doing some fixup

Tesses.WebServer.NetStandard/ServerContext.cs

@@ -3,6 +3,7 @@ using System.IO;
 using System;
 using System.Net;
 using System.Text;
+using System.Threading;
 
 namespace Tesses.WebServer
 {
@@ -71,6 +72,17 @@ internal class SizedStream : Stream
 }
     public class ServerContext
     {
+            static Mutex mtx=new Mutex();
+        static long _unique=0;
+
+        public static long UniqueNumber()
+        {
+            mtx.WaitOne();
+            long u=_unique++;
+            mtx.ReleaseMutex();
+            return u;
+        }
+
         const string bad_chars = "<>?/\\\"*|:";
         public static string FixFileName(string filename,bool requireAscii=false)
         {