fixed concurrent incrementation problems

src/main/scala/org/tbasket/EndpointSetup.scala

@@ -1,7 +1,7 @@
 package org.tbasket
 
 import org.tbasket.api.Endpoint
-import org.tbasket.compute.IncrementHandler
+import org.tbasket.handler.IncrementHandler
 
 import java.util.Properties
 

src/main/scala/org/tbasket/handler/IncrementHandler.scala

@@ -1,20 +1,22 @@
-package org.tbasket.compute
+package org.tbasket.handler
 
 import org.tbasket.api.compute.APIRequestHandler
 import zio.http.{Request, Response}
 
+import java.util.concurrent.atomic.AtomicInteger
+
 object IncrementHandler extends APIRequestHandler {
 
-    @volatile private var i = 0
+    private val i = new AtomicInteger(0)
 
-    def getCounter: Int = i
+    def getCounter: Int = i.get()
 
     override def get(request: Request): Response = {
         Response.json(s"{\"value\": $i}")
     }
 
     override def post(request: Request): Response = {
-        i += 1
+        i.incrementAndGet()
         println(s"Counter is now $i")
         Response.ok
     }

src/test/scala/org/tbasket/test/IncrementRequestHandler.scala

@@ -2,7 +2,7 @@ package org.tbasket.test
 
 import io.circe.parser._
 import org.junit.jupiter.api.{Assertions, Test}
-import org.tbasket.compute.IncrementHandler
+import org.tbasket.handler.IncrementHandler
 import zio.http.model.Status
 import zio.http.{Body, Path, Request, URL}