sync-wait-group

A port of golang sync.WaitGroup

Example

``js
const WaitGroup = require("sync-wait-group").WaitGroup;

async function main() {
const wg = new WaitGroup();
let n = 0;

wg.add(1);
(async () => {
n++;
wg.done();
})();

wg.add(1);
(async () => {
n++;
wg.done();
})();

await wg.wait();
cassert.equal(n, 2);
}
`

Docs

$3

Creates a wait group instance. This instance contains a cached
promise that is used when wait() is called so once the waitgroup
is finished this object cannot be re-used.

It's safe to call wait() if you do not call add() ; aka the
internal counter === 0.

It's safe to call wait() multiple times.
It's safe to call wait() after done() has been called and
the waitgroup is already finished.

This pattern is considered better then creating a Deferred

`js
// Instead of using deferred use WaitGroup
const d = new Deferred();

(async () => {
d.resolve();
})();

await d.promise();

// This is preferred as it's more clear what your intent is.
// When you use deferred it's confusing why you didn't use
// new Promise((resolve, reject) => { ... }) instead.
const wg = new WaitGroup();
wg.add(1);

(async () => {
wg.done();
})();

await wg.wait();
`

$3

Increments the counter of pending work that your waiting for by
N.

If your waiting for a single event you can call wg.add(1)

If your implementing fanout or scatter gather then you can call
wg.add(number_of_tasks)

If you call add() after the waitgroup is finished, aka the
internal counter has been decremented to 0 by done() then
an exception is thrown.

$3

Call done() to notify that a piece of work your waiting for
has completed. This will decrement the internal counter by 1.

If the counter is 0 then all the promises returned from
wg.wait() will resolve successfully.

If calling done() would make the counter negative then an
exception is thrown.

$3

Returns a cached Promise that resolves once the wg has finished.
This happens when done() has been called enough to decrement
the counter increased by add(n).

If you call wait() without calling add() or done() then
it returns a resolved promise.

Installation

npm install sync-wait-group

Tests

npm test`

Contributors

- Raynos

MIT Licensed

[build-png]: https://secure.travis-ci.org/Raynos/sync-wait-group.png
[build]: https://travis-ci.org/Raynos/sync-wait-group
[cover-png]: https://coveralls.io/repos/Raynos/sync-wait-group/badge.png
[cover]: https://coveralls.io/r/Raynos/sync-wait-group
[dep-png]: https://david-dm.org/Raynos/sync-wait-group.png
[dep]: https://david-dm.org/Raynos/sync-wait-group
[npm-png]: https://nodei.co/npm/sync-wait-group.png?stars&downloads
[npm]: https://nodei.co/npm/sync-wait-group