diff --git a/Sources/AWSLambdaRuntime/Lambda+LocalServer.swift b/Sources/AWSLambdaRuntime/Lambda+LocalServer.swift
index 731ca597..02607680 100644
--- a/Sources/AWSLambdaRuntime/Lambda+LocalServer.swift
+++ b/Sources/AWSLambdaRuntime/Lambda+LocalServer.swift
@@ -59,7 +59,7 @@ private enum LocalLambda {
             var logger = Logger(label: "LocalLambdaServer")
             logger.logLevel = configuration.general.logLevel
             self.logger = logger
-            self.group = MultiThreadedEventLoopGroup(numberOfThreads: System.coreCount)
+            self.group = MultiThreadedEventLoopGroup(numberOfThreads: 1)
             self.host = configuration.runtimeEngine.ip
             self.port = configuration.runtimeEngine.port
             self.invocationEndpoint = invocationEndpoint ?? "/invoke"
@@ -88,13 +88,20 @@ private enum LocalLambda {
     }
 
     final class HTTPHandler: ChannelInboundHandler {
+        
+        enum InvocationState {
+            case waitingForNextRequest
+            case idle(EventLoopPromise<Pending>)
+            case processing(Pending)
+        }
+        
         public typealias InboundIn = HTTPServerRequestPart
         public typealias OutboundOut = HTTPServerResponsePart
 
-        private static let queueLock = Lock()
-        private static var queue = [String: Pending]()
-
         private var processing = CircularBuffer<(head: HTTPRequestHead, body: ByteBuffer?)>()
+        
+        private static var queue = [Pending]()
+        private static var invocationState: InvocationState = .waitingForNextRequest
 
         private let logger: Logger
         private let invocationEndpoint: String
@@ -137,43 +144,63 @@ private enum LocalLambda {
                             self.writeResponse(context: context, response: .init(status: .internalServerError))
                         }
                     }
-                    Self.queueLock.withLock {
-                        Self.queue[requestId] = Pending(requestId: requestId, request: work, responsePromise: promise)
+                    let pending = Pending(requestId: requestId, request: work, responsePromise: promise)
+                    switch Self.invocationState {
+                    case .idle(let promise):
+                        promise.succeed(pending)
+                    case .processing(_), .waitingForNextRequest:
+                        Self.queue.append(pending)
                     }
                 }
             } else if request.head.uri.hasSuffix("/next") {
-                switch (Self.queueLock.withLock { Self.queue.popFirst() }) {
+                // check if our server is in the correct state
+                guard case .waitingForNextRequest = Self.invocationState else {
+                    #warning("better error code?!")
+                    self.writeResponse(context: context, response: .init(status: .conflict))
+                    return
+                }
+                
+                // pop the first task from the queue
+                switch !Self.queue.isEmpty ? Self.queue.removeFirst() : nil {
                 case .none:
-                    self.writeResponse(context: context, response: .init(status: .noContent))
-                case .some(let pending):
-                    var response = Response()
-                    response.body = pending.value.request
-                    // required headers
-                    response.headers = [
-                        (AmazonHeaders.requestID, pending.key),
-                        (AmazonHeaders.invokedFunctionARN, "arn:aws:lambda:us-east-1:\(Int16.random(in: Int16.min ... Int16.max)):function:custom-runtime"),
-                        (AmazonHeaders.traceID, "Root=\(Int16.random(in: Int16.min ... Int16.max));Parent=\(Int16.random(in: Int16.min ... Int16.max));Sampled=1"),
-                        (AmazonHeaders.deadline, "\(DispatchWallTime.distantFuture.millisSinceEpoch)"),
-                    ]
-                    Self.queueLock.withLock {
-                        Self.queue[pending.key] = pending.value
+                    // if there is nothing in the queue, create a promise that we can succeed,
+                    // when we get a new task
+                    let promise = context.eventLoop.makePromise(of: Pending.self)
+                    promise.futureResult.whenComplete { (result) in
+                        switch result {
+                        case .failure(let error):
+                            self.writeResponse(context: context, response: .init(status: .internalServerError))
+                        case .success(let pending):
+                            Self.invocationState = .processing(pending)
+                            self.writeResponse(context: context, response: pending.toResponse())
+                        }
                     }
-                    self.writeResponse(context: context, response: response)
+                    Self.invocationState = .idle(promise)
+                case .some(let pending):
+                    // if there is a task pending, we can immediatly respond with it.
+                    Self.invocationState = .processing(pending)
+                    self.writeResponse(context: context, response: pending.toResponse())
                 }
 
             } else if request.head.uri.hasSuffix("/response") {
                 let parts = request.head.uri.split(separator: "/")
                 guard let requestId = parts.count > 2 ? String(parts[parts.count - 2]) : nil else {
+                    // the request is malformed, since we were expecting a requestId in the path
                     return self.writeResponse(context: context, response: .init(status: .badRequest))
                 }
-                switch (Self.queueLock.withLock { Self.queue[requestId] }) {
-                case .none:
-                    self.writeResponse(context: context, response: .init(status: .badRequest))
-                case .some(let pending):
-                    pending.responsePromise.succeed(.init(status: .ok, body: request.body))
-                    self.writeResponse(context: context, response: .init(status: .accepted))
-                    Self.queueLock.withLock { Self.queue[requestId] = nil }
+                guard case .processing(let pending) = Self.invocationState else {
+                    // a response was send, but we did not expect to receive one
+                    #warning("better error code?!")
+                    return self.writeResponse(context: context, response: .init(status: .conflict))
                 }
+                guard requestId == pending.requestId else {
+                    // the request's requestId is not matching the one we are expecting
+                    return self.writeResponse(context: context, response: .init(status: .badRequest))
+                }
+                
+                pending.responsePromise.succeed(.init(status: .ok, body: request.body))
+                self.writeResponse(context: context, response: .init(status: .accepted))
+                Self.invocationState = .waitingForNextRequest
             } else {
                 self.writeResponse(context: context, response: .init(status: .notFound))
             }
@@ -211,6 +238,19 @@ private enum LocalLambda {
             let requestId: String
             let request: ByteBuffer
             let responsePromise: EventLoopPromise<Response>
+            
+            func toResponse() -> Response {
+                var response = Response()
+                response.body = self.request
+                // required headers
+                response.headers = [
+                    (AmazonHeaders.requestID, self.requestId),
+                    (AmazonHeaders.invokedFunctionARN, "arn:aws:lambda:us-east-1:\(Int16.random(in: Int16.min ... Int16.max)):function:custom-runtime"),
+                    (AmazonHeaders.traceID, "Root=\(Int16.random(in: Int16.min ... Int16.max));Parent=\(Int16.random(in: Int16.min ... Int16.max));Sampled=1"),
+                    (AmazonHeaders.deadline, "\(DispatchWallTime.distantFuture.millisSinceEpoch)"),
+                ]
+                return response
+            }
         }
     }