diff --git a/src/index.ts b/src/index.ts
index 2ac3d21e..d3e732bc 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -12,6 +12,7 @@ import {
   randomUUID,
   sanitizeFunctionArguments,
 } from "./utils.js";
+import { execLocally, setupFn } from "./local.js";
 
 const withDelay = (dt: Date, delay: Duration): Date =>
   new Date(dt.getTime() + parseDuration(delay)!);
@@ -31,39 +32,6 @@ function getHTTPClient(): HTTPClient | undefined {
 
 export const deferEnabled = () => !!getEnv("DEFER_TOKEN");
 
-async function execLocally(
-  id: string,
-  fn: any,
-  args: any
-): Promise<client.FetchExecutionResponse> {
-  let state: client.ExecutionState = "succeed";
-  let originalResult: any;
-  try {
-    originalResult = await fn(...args);
-  } catch (error) {
-    const e = error as Error;
-    state = "failed";
-    originalResult = {
-      name: e.name,
-      message: e.message,
-      cause: e.cause,
-      stack: e.stack,
-    };
-  }
-
-  let result: any;
-  try {
-    result = JSON.parse(JSON.stringify(originalResult || ""));
-  } catch (error) {
-    const e = error as Error;
-    throw new DeferError(`cannot serialize function return: ${e.message}`);
-  }
-
-  const response = { id, state, result };
-  __database.set(id, response);
-
-  return response;
-}
 
 async function enqueue<F extends DeferableFunction>(
   func: DeferredFunction<F>,
@@ -105,7 +73,7 @@ async function enqueue<F extends DeferableFunction>(
 
   const id = randomUUID();
   __database.set(id, { id: id, state: "started" });
-  execLocally(id, originalFunction, functionArguments);
+  execLocally(id, func, functionArguments)
   return { id };
 }
 
@@ -139,6 +107,8 @@ export type Concurrency = Range<0, 51>;
 export type NextRouteString = `/api/${string}`;
 
 export interface Manifest {
+  id: string;
+  name: string;
   version: number;
   cron?: string;
   retry?: RetryPolicy;
@@ -249,12 +219,16 @@ export function defer<F extends DeferableFunction>(
 
   wrapped.__fn = fn;
   wrapped.__metadata = {
+    id: randomUUID(),
+    name: fn.name,
     version: INTERNAL_VERSION,
     retry: parseRetryPolicy(config),
     concurrency: config?.concurrency,
     maxDuration: config?.maxDuration,
   };
 
+  setupFn(wrapped.__metadata)
+
   return wrapped;
 }
 
@@ -271,6 +245,8 @@ defer.cron = function (
 
   wrapped.__fn = fn;
   wrapped.__metadata = {
+    id: randomUUID(),
+    name: fn.name,
     version: INTERNAL_VERSION,
     retry: parseRetryPolicy(config),
     cron: cronExpr,
@@ -361,7 +337,7 @@ export function awaitResult<F extends DeferableFunction>(
     } else {
       const id = randomUUID();
       __database.set(id, { id: id, state: "started" });
-      response = await execLocally(id, originalFunction, functionArguments);
+      response = await execLocally(id, fn, functionArguments);
     }
 
     if (response.state === "failed") {
diff --git a/src/local.ts b/src/local.ts
new file mode 100644
index 00000000..4334fb20
--- /dev/null
+++ b/src/local.ts
@@ -0,0 +1,76 @@
+import { ExecutionState, FetchExecutionResponse } from "./client.js";
+import { DeferError } from "./errors.js";
+import {
+  DeferredFunction,
+  __database,
+  DeferableFunction,
+  Manifest,
+} from "./index";
+import { Queue } from "./queue.js";
+
+type Invocation<F extends DeferableFunction> = {
+  id: string;
+  func: DeferredFunction<F>
+  args: any
+  oncomplete: ((result: FetchExecutionResponse<any>) => void) | undefined
+};
+type FunctionConfiguration<F extends DeferableFunction> = Manifest & {
+  queue: Queue<Invocation<F>>;
+};
+const fns: Record<string, FunctionConfiguration<any>> = {};
+
+export function setupFn<F extends DeferableFunction>(metadata: Manifest) {
+  fns[metadata.id] = {
+    ...metadata,
+    queue: new Queue<Invocation<F>>(invoke, metadata.concurrency),
+  };
+}
+
+export function execLocally<F extends DeferableFunction>(
+  id: string,
+  func: DeferredFunction<F>,
+  args: any
+): Promise<FetchExecutionResponse<any>> {
+  return new Promise(resolve => {
+    fns[func.__metadata.id]!.queue.push({
+      id,
+      func,
+      args,
+      oncomplete: resolve
+    });
+  })
+}
+
+async function invoke(invocation: Invocation<any>) {
+    __database.set(invocation.id, { id: invocation.id, state: "started" });
+    let state: ExecutionState = "succeed";
+    let originalResult: any;
+    try {
+      originalResult = await invocation.func.__fn(...invocation.args);
+    } catch (error) {
+      const e = error as Error;
+      state = "failed";
+      originalResult = {
+        name: e.name,
+        message: e.message,
+        cause: e.cause,
+        stack: e.stack,
+      };
+
+      console.error('Error in deferred function ' + invocation.func.__fn.name + ' (invocation ' + invocation.id + '):\n', e)
+    }
+  
+    let result: any;
+    try {
+      result = JSON.parse(JSON.stringify(originalResult || ""));
+    } catch (error) {
+      const e = error as Error;
+      throw new DeferError(`cannot serialize function return: ${e.message}`);
+    }
+  
+    const response = { id: invocation.id, state, result }
+    __database.set(invocation.id, response);
+
+    invocation.oncomplete?.(response)
+  
+}
\ No newline at end of file
diff --git a/src/queue.ts b/src/queue.ts
new file mode 100644
index 00000000..bdbba603
--- /dev/null
+++ b/src/queue.ts
@@ -0,0 +1,33 @@
+import { Concurrency } from ".";
+
+export class Queue<T> extends Array<T> {
+  private running = 0;
+
+  constructor(public invoker: (item: T) => Promise<void>, public concurrency?: Concurrency) {
+    super();
+    Object.setPrototypeOf(this, Queue.prototype)
+  }
+
+  override push(...items: T[]): number {
+    const len = super.push(...items);
+    this.next();
+    return len;
+  }
+
+  private next() {
+    if (!this.concurrency || this.running < this.concurrency) {
+      this.dequeue();
+    }
+  }
+
+  private dequeue() {
+    const item = this.shift();
+    if (item) {
+      ++this.running;
+      this.invoker(item).finally(() => {
+        --this.running;
+        this.next();
+      });
+    }
+  }
+}