diff --git a/utils/async-lock.mjs b/utils/async-lock.mjs
new file mode 100644
index 0000000..9e55e2b
--- /dev/null
+++ b/utils/async-lock.mjs
@@ -0,0 +1,35 @@
+import { Queue } from './queue.mjs';
+
+export class AsyncLock {
+	constructor() {
+		this.pending_queue = new Queue();
+		this.state = false;
+		this.lock_id = 0;
+	}
+
+	query() {
+		return this.state;
+	}
+
+	acquire() {
+		if (!this.state) {
+			this.state = true;
+			this.lock_id += 1;
+			return Promise.resolve(this.lock_id);
+		}
+		return new Promise((resolve, _reject) => this.pending_queue.push(resolve));
+	}
+
+	release(lock_id) {
+		if (lock_id != this.lock_id) { return; }
+		if (this.pending_queue.empty()) {
+			this.state = false;
+			return;
+		}
+
+		let resolve = this.pending_queue.front();
+		this.pending_queue.popFront();
+		this.lock_id += 1;
+		resolve(lock_id);
+	}
+};
diff --git a/utils/index.mjs b/utils/index.mjs
index db4c85e..eeaa85c 100644
--- a/utils/index.mjs
+++ b/utils/index.mjs
@@ -1,5 +1,6 @@
 import fs from 'node:fs/promises';
 
+// Reads JSON data from file, returns null if file not found or has other errors.
 export async function readJsonFile(path) {
 	try {
 		const data = await fs.readFile(path, 'utf8');
@@ -9,21 +10,54 @@ export async function readJsonFile(path) {
 	}
 }
 
+// Write JSON data into a file.
 export function writeJsonFile(path, data) {
 	const json_string = JSON.stringify(data);
 	return fs.writeFile(path, json_string, 'utf8');
 }
 
+// Parse format "profile@host:port", port can be undefined.
 export function parseLogin(url) {
 	const [profile_host, port] = url.split(':');
 	const [profile, host] = profile_host.split('@');
 	return [profile, host, port ? parseInt(port) : undefined];
 }
 
+// Returns a promise, wait unitl the EventEmitter emits certian event next time.
 export function waitEvent(em, event) {
 	return new Promise((resolve, _reject) => {
 		em.once(event, resolve);
 	});
 }
 
-export default { readJsonFile, writeJsonFile, parseLogin, waitEvent };
+export function asyncSleep(t) {
+	return new Promise((resolve, _reject) => {
+		setTimeout(resolve, t);
+	});
+}
+
+export function asyncTimeout(t) {
+	return new Promise((_resolve, reject) => {
+		setTimeout(reject, t);
+	});
+}
+
+export function promiseTimeout(p, t) {
+	return Promise.race([p, asyncTimeout(t)]);
+}
+
+export function yieldTask() {
+	return new Promise((resolve, _reject) => {
+		queueMicrotask(resolve);
+	});
+}
+
+// Checks wheather an object is iterable.
+export function isIterable(obj) {
+	if (obj == null) { return false; }
+	return typeof obj[Symbol.iterator] == 'function';
+}
+
+export { Queue, QueueEmptyError } from './queue.mjs';
+export { AsyncLock } from './async-lock.mjs';
+export { Task, TaskInteruptedError } from './task.mjs';
diff --git a/utils/package.json b/utils/package.json
new file mode 100644
index 0000000..6b9a837
--- /dev/null
+++ b/utils/package.json
@@ -0,0 +1,6 @@
+{
+	"name": "@fang_erj/compass-utils",
+	"description": "Utility functions use in compass-bot",
+	"type": "module",
+	"main": "index.mjs"
+}
diff --git a/utils/queue.mjs b/utils/queue.mjs
new file mode 100644
index 0000000..14f1c32
--- /dev/null
+++ b/utils/queue.mjs
@@ -0,0 +1,62 @@
+export class QueueEmptyError extends Error {
+	constructor() { super('Queue is empty'); }
+}
+
+export class Queue {
+	constructor() {
+		this.data = [];
+		this.head = 0;
+	}
+
+	front() {
+		return this.data[this.head];
+	}
+
+	back() {
+		return this.data[this.data.length - 1];
+	}
+
+	popBack() {
+		if (this.data.length == this.head) {
+			throw new QueueEmptyError();
+		}
+		this.data.length -= 1;
+	}
+
+	empty() {
+		return this.data.length == this.head;
+	}
+
+	size() {
+		return this.data.length - this.head;
+	}
+
+	get length() {
+		return this.size();
+	}
+
+	push() {
+		this.data.push.apply(this.data, arguments);
+	}
+
+	popFront() {
+		if (this.empty()) { throw new QueueEmptyError();}
+
+		this.head += 1;
+		if (this.head == this.data.length) {
+			this.data = [];
+			this.head = 0;
+			return;
+		}
+		if (this.head >= this.data.length >> 1 && this.head >= 16) {
+			this.data = this.data.slice(this.head);
+			this.head = 0;
+		}
+	}
+
+	*[Symbol.iterator]() {
+		for (let i = this.head; i < this.data.length; i += 1) {
+			yield this.data[i];
+		}
+	}
+}
diff --git a/utils/task.mjs b/utils/task.mjs
new file mode 100644
index 0000000..34f0b12
--- /dev/null
+++ b/utils/task.mjs
@@ -0,0 +1,81 @@
+export class TaskInteruptedError {
+	constructor() { super('Task has been interupted.'); }
+};
+
+export class Task {
+	constructor() {
+		this.status = Task.STATUS.pending;
+		this.error = null;
+		this.result = null;
+		this.result_listeners = [];
+	}
+
+	_ready(result) {
+		this.result = result;
+		this.status = Task.STATUS.ready;
+		this.#notifySuccess();
+	}
+
+	_fail(error) {
+		if (this.status == Task.STATUS.interupted) { return; }
+		this.error = error;
+		this.status = Task.STATUS.failed;
+		this.#notifyFailure();
+	}
+
+	_start() {
+		if (this.status != Task.STATUS.pending) {
+			throw new Error('Task has already left pending stage');
+		}
+		this.status = Task.STATUS.running;
+	}
+
+	interupt() {
+		if (this.status == Task.STATUS.pending) { this._confirmInterupt(); }
+		else { this.status = Task.STATUS.interupting; }
+	}
+
+	_shouldInterupt() {
+		return this.status == Task.STATUS.interupting;
+	}
+
+	_confirmInterupt() {
+		this.status = Task.STATUS.interupted;
+		this.error = new TaskInteruptedError();
+		this.#notifyFailure();
+	}
+
+	get() {
+		if (this.status == Task.STATUS.ready) { return Promise.resolve(this.result); }
+		if (this.status == Task.STATUS.failed || this.status == Task.STATUS.interupted) {
+			return Promise.reject(this.error);
+		}
+
+		return new Promise((resolve, reject) => {
+			this.result_listeners.push([resolve, reject]);
+		});
+	}
+
+	#notifyFailure() {
+		for (let [_resolve, reject] of this.result_listeners) {
+			reject(this.error);
+		}
+		this.result_listeners = [];
+	}
+
+	#notifySuccess() {
+		for (let [resolve, _reject] of this.result_listeners) {
+			resolve(this.result);
+		}
+		this.result_listeners = [];
+	}
+};
+
+Task.STATUS = {
+	pending: 0,
+	running: 1,
+	interupting: 2,
+	ready: 3,
+	interupted: 4,
+	failed: 5,
+};