Clarification needed about WCF Concurrency in REST Services -

i have created wcf rest services. when hitting same request continuously client(i.e android mobile) using diifrerent threads , thread.sleep not working.

my code below this..

[servicebehavior(instancecontextmode = instancecontextmode.percall, concurrencymode = concurrencymode.single)]     public class service1 : iservice1     {       [webinvoke(method = "post", requestformat = webmessageformat.json, responseformat = webmessageformat.json, bodystyle = webmessagebodystyle.bare, uritemplate = "verifylogin")]         public bool verifylogin(login logincred)         {             bool res = false;             string strthreadprint= "";             try             {                strthreadprint= thread.currentthread.managedthreadid.tostring() + "  time @ : "+datetime.now;                thread.sleep(5000);                 dbcon = new dbconnection(); //for testing here throwing exception going catch block , responce sent client exception details shown in catch block.                dbcon.verifylogin(logincred.username.trim(), logincred.password.trim());              }             catch (exception sqlex)             {                 objerrorclass = new errorclass("login class", sqlex.message + " --- " + strthreadprint, "cnmk");                 throw new webfaultexception<errorclass>(objerrorclass, system.net.httpstatuscode.badrequest);              }         }     } 

when sending request using fiddler following requestbody {"username":"13","password":"dgdf"}

at time getting responce in json format

response service:  {"errordesc":"login failed --- 33 time @ :09/04/2013 12:31:30"} {"errordesc":"login failed --- 35 time @ :09/04/2013 12:31:30"} {"errordesc":"login failed --- 41 time @ :09/04/2013 12:31:30"} {"errordesc":"login failed --- 45 time @ :09/04/2013 12:31:30"} 

so instance mode , concurrency mode not working wcf restful services???? or doing wrong in code?? please me

if understand correctly want have wcf host single instance of service operation , have service wait 5 seconds before responding?

if should use instancecontextmode.single, mean service requests routed same instance of service processing.

edit

i don't understand behavior want see. have 4 concurrent requests, have per call service instance, have 4 requests processed @ same time 4 different service instances. cannot see problem output.

edit2

concurrencymode determine how each instance of service deals concurrent requests dispatched instance.

however, specifying instance per call. have 4 calls, therefore have 4 instances of service net result each call processed concurrently.

so behavior observing correct way have configured service.

if want single service instance process calls need specify instancecontextmode.single.