chocof / promise-queue

A queue implementation which allows two or more asynchronous resources to communicate

PromiseQueue

PromiseQueue allows you to write data into a queue and then read them from any other asynchronous callback. Write and read functions are blocking.

Usage

To generate a PromiseQueue instance simply provide its size const pp = new PromiseQueue(size) if size is not supplied then the queues' write operation will never block.

In order to use the module you just have to be accustomed to its two main functions:

• pp.write(data: any): Write data on one end of the queue. This operation will block if the queue is full (the number of itams is equal to the size of the queue).
• pp.read(): Read data from the other end of the the queue. If the queue is empty the function will block. Returns objects from the queue in the form { data: any }. If the queue is closed it returns null.

To close the queue call pp.close(). An example usage is provided bellow:

const PromiseQueue = require('../src');

const pp = new PromiseQueue(2);

setTimeout(async () => {
  await pp.write(1)
}, 100);
setTimeout(async () => {
  await pp.write(2)
}, 200);
setTimeout(async () => {
  await pp.write(3)
}, 300);
setTimeout(async () => {
  await pp.write(4)
}, 400);
setTimeout(() => {
  pp.close()
}, 500);

let result;
(async () => {
  while (result  = await pp.read()) {
    console.log("RECEIVED", result.data);
  }
  console.log("FINI");
  // will print 1, 2, 3, 4, FINI
}) ()

If you provide a size then .write() functions will be blocked until there is some free space.

const PromiseQueue = require('../src');

const pp = new PromiseQueue(1);
setTimeout(async () => {
  console.log(await pp.read())
}, 100);
setTimeout(async () => {
  console.log(await pp.read())
}, 200);
setTimeout(async () => {
  console.log(await pp.read())
}, 1000);
setTimeout(async () => {
  console.log(await pp.read())
}, 2000);
setTimeout(() => {
  pp.close()
}, 3000);

let result;
(async () => {
  console.log("WRITTING",1)
  await pp.write(1)
  console.log("WRITTING",2)
  console.log("Will have to wait until 1 is consumed to continue")
  await pp.write(2)
  console.log("WRITTING",3)
  console.log("Will have to wait until 2 is consumed to continue")
  await pp.write(3)
  console.log("WRITTING",4)
  console.log("Will have to wait until 3 is consumed to continue")
  await pp.write(4)

  console.log("FINI");
}) ()