jquery - xmlHttpRequest/AJAX Calls are blocking all Servlet calls after refreshing 3 times -

i trying data ui making ajax calls servlet. following code using make these calls,

function callservlet(paramstring, mapping){     var url = contextpath + "/" + mapping;     var strobj;     $.ajax({      url: url,     data: paramstring,     type: 'post',     async : false,     cache : false,     beforesend:function(){       console.log("hello");     },     success: function(data) {       if (data) {       console.log('data', data);       strobj = data;      }     },     error:function(a,b,e)     {       console.log(e);     }   });  return strobj; } 

i have 5 of these calls done when page loads populate various parts of ui. after refresh page 3 times, page gets stuck @ 1 of these 5 servlet calls. when restart tomcat server, works expected 3 times , gets stuck again.

note: able make numerous calls above used servlet postman client. gets stuck when use ajax or xmlhttprequest call servlet.

can suggest can issue? please ask if other information needed.