async

Asynchronous primitive modules for Deno.

Usage

Barrier

Barrier is a synchronization primitive that allows multiple tasks to wait until all of them have reached a certain point of execution before continuing.

import { Barrier } from "https://deno.land/x/async@v2.1.0/barrier.ts";

const barrier = new Barrier(3);

async function worker(id: number) {
  console.log(`worker ${id} is waiting`);
  await barrier.wait();
  console.log(`worker ${id} is done`);
}

worker(1);
worker(2);
worker(3);

WaitGroup

WaitGroup is a synchronization primitive that enables promises to coordinate and synchronize their execution. It is particularly useful in scenarios where a specific number of tasks must complete before the program can proceed.

import { delay } from "https://deno.land/std@0.211.0/async/delay.ts";
import { WaitGroup } from "https://deno.land/x/async@v2.1.0/wait_group.ts";

const wg = new WaitGroup();

async function worker(id: number) {
  wg.add(1);
  console.log(`worker ${id} is waiting`);
  await delay(100);
  console.log(`worker ${id} is done`);
  wg.done();
}

worker(1);
worker(2);
worker(3);
await wg.wait();

Lock/RwLock

Lock is a mutual exclusion lock that provides safe concurrent access to a shared value.

import { AsyncValue } from "https://deno.land/x/async@v2.1.0/testutil.ts";
import { Lock } from "https://deno.land/x/async@v2.1.0/lock.ts";

// Critical section
const count = new Lock(new AsyncValue(0));
await count.lock(async (count) => {
  const v = await count.get();
  count.set(v + 1);
});

RwLock is a reader-writer lock implementation that allows multiple concurrent reads but only one write at a time. Readers can acquire the lock simultaneously as long as there are no writers holding the lock. Writers block all other readers and writers until the write operation completes.

import { AsyncValue } from "https://deno.land/x/async@v2.1.0/testutil.ts";
import { RwLock } from "https://deno.land/x/async@v2.1.0/rw_lock.ts";

const count = new RwLock(new AsyncValue(0));

// rlock should allow multiple readers at a time
await Promise.all([...Array(10)].map(() => {
  return count.rlock(async (count) => {
    console.log(await count.get());
  });
}));

// lock should allow only one writer at a time
await Promise.all([...Array(10)].map(() => {
  return count.lock(async (count) => {
    const v = await count.get();
    console.log(v);
    count.set(v + 1);
  });
}));

Mutex

Mutex is a mutex (mutual exclusion) is a synchronization primitive that grants exclusive access to a shared resource.

This is a low-level primitive. Use Lock instead of Mutex if you need to access a shared value concurrently.

import { AsyncValue } from "https://deno.land/x/async@v2.1.0/testutil.ts";
import { Mutex } from "https://deno.land/x/async@v2.1.0/mutex.ts";

const count = new AsyncValue(0);

async function doSomething() {
  const v = await count.get();
  await count.set(v + 1);
}

// Critical section
const mu = new Mutex();
await mu.acquire();
try {
  await doSomething();
} finally {
  mu.release();
}

Notify

Notify is an async notifier that allows one or more “waiters” to wait for a notification.

import { assertEquals } from "https://deno.land/std@0.211.0/assert/mod.ts";
import { promiseState } from "https://deno.land/x/async@v2.1.0/state.ts";
import { Notify } from "https://deno.land/x/async@v2.1.0/notify.ts";

const notify = new Notify();
const waiter1 = notify.notified();
const waiter2 = notify.notified();
notify.notify();
assertEquals(await promiseState(waiter1), "fulfilled");
assertEquals(await promiseState(waiter2), "pending");
notify.notify();
assertEquals(await promiseState(waiter1), "fulfilled");
assertEquals(await promiseState(waiter2), "fulfilled");

Queue/Stack

Queue is a queue implementation that allows for adding and removing elements, with optional waiting when popping elements from an empty queue.

import { assertEquals } from "https://deno.land/std@0.211.0/assert/mod.ts";
import { Queue } from "https://deno.land/x/async@v2.1.0/queue.ts";

const queue = new Queue<number>();
queue.push(1);
queue.push(2);
queue.push(3);
assertEquals(await queue.pop(), 1);
assertEquals(await queue.pop(), 2);
assertEquals(await queue.pop(), 3);

Stack is a stack implementation that allows for adding and removing elements, with optional waiting when popping elements from an empty stack.

import { assertEquals } from "https://deno.land/std@0.211.0/assert/mod.ts";
import { Stack } from "https://deno.land/x/async@v2.1.0/stack.ts";

const stack = new Stack<number>();
stack.push(1);
stack.push(2);
stack.push(3);
assertEquals(await stack.pop(), 3);
assertEquals(await stack.pop(), 2);
assertEquals(await stack.pop(), 1);

Semaphore

A semaphore that allows a limited number of concurrent executions of an operation.

import { Semaphore } from "https://deno.land/x/async@v2.1.0/semaphore.ts";

const sem = new Semaphore(5);
const worker = () => {
  return sem.lock(async () => {
    // do something
  });
};
await Promise.all([...Array(10)].map(() => worker()));

promiseState

promiseState is used to determine the state of the promise. Mainly for testing purpose.

import { promiseState } from "https://deno.land/x/async@v2.1.0/mod.ts";

const p1 = Promise.resolve("Resolved promise");
console.log(await promiseState(p1)); // fulfilled

const p2 = Promise.reject("Rejected promise").catch(() => undefined);
console.log(await promiseState(p2)); // rejected

const p3 = new Promise(() => undefined);
console.log(await promiseState(p3)); // pending

AsyncValue

AsyncValue is a class that wraps a value and allows it to be set asynchronously.

import { assertEquals } from "https://deno.land/std@0.211.0/assert/mod.ts";
import { AsyncValue } from "https://deno.land/x/async@v2.1.0/testutil.ts";

const v = new AsyncValue(0);
assertEquals(await v.get(), 0);
await v.set(1);
assertEquals(await v.get(), 1);

License

The code follows MIT license written in LICENSE. Contributors need to agree that any modifications sent in this repository follow the license.