# await-semaphore

> Awaitable semaphore/mutex

Latest version **0.1.3** (published 2017-09-27) · MIT license · 0 weekly downloads

## Install

```sh
npm install await-semaphore
pnpm add await-semaphore
yarn add await-semaphore
bun add await-semaphore
```

## Health

**Score 15/100 (F)** — status: abandoned.

Positive: no vulnerabilities.

Warnings: low downloads; no types; no esm support; pre 1.0.

Negative: abandoned; low maintenance score.

## Facts

| | |
|---|---|
| Version | 0.1.3 |
| Published | 2017-09-27 |
| First published | 2016-07-22 |
| Weekly downloads | 0 |
| License | MIT |
| TypeScript types | none |
| Module format | CommonJS |
| Dependencies | 0 |
| Known vulnerabilities | 0 |
| Install scripts | no |
| GitHub stars | 70 |
| Author | Emma Kuo |
| Maintainers | notenoughneon |
| Keywords | promise, semaphore, mutex, typescript |

## Links

- npm: https://www.npmjs.com/package/await-semaphore
- Repository: https://github.com/notenoughneon/await-semaphore
- Homepage: https://github.com/notenoughneon/await-semaphore#readme
- Issues: https://github.com/notenoughneon/await-semaphore/issues
- npm.io page: https://npm.io/package/await-semaphore

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## Recent versions

- 0.1.3 (latest) — 2017-09-27
- 0.1.2 — 2017-09-02
- 0.1.1 — 2016-07-29
- 0.1.0 — 2016-07-22

## README

# await-semaphore
Awaitable semaphore/mutex

A semaphore implementation using ES6 promises and supporting 3 styles:

* async/await style (needs typescript)
* thunk style (automatic acquire/release)
* promise style

Also includes `Mutex` as a convenience for `new Semaphore(1)`.

## API

### new Semaphore(count: number)

Create a new semaphore with the given count.

```javascript
import {Semaphore} from 'await-semaphore';

var semaphore = new Semaphore(10);
```

### semaphore.acquire(): Promise<() => void>

Acquire the semaphore and returns a promise for the release function. Be sure to handle release for exception case.

```javascript
semaphore.acquire()
.then(release => {
    //critical section...
    doSomething()
    .then(res => {
        //...
        release();
    })
    .catch(err => {
        //...
        release();
    });
});
```

### semaphore.use<T>(thunk: () => Promise<T>): Promise<T>

Alternate method for using the semaphore by providing a thunk. This automatically handles acquire/release.

```javascript
semaphore.use(() => {
    //critical section...
});
```

### new Mutex()

An alias for `new Semaphore(1)`. Mutex has the same methods as Semaphore.

```javascript
import {Mutex} from 'await-semaphore';

var mutex = new Mutex();
```

## Examples

Create a version of `fetch()` with concurrency limited to 10.

### async/await style (typescript)

```typescript
var semaphore = new Semaphore(10);

async function niceFetch(url) {
    var release = await semaphore.acquire();
    var result = await fetch(url);
    release();
    return result;
}
```

### thunk style (javascript)

```javascript
var semaphore = new Semaphore(10);

function niceFetch(url) {
    return semaphore.use(() => fetch(url));
}
```

### promise style (javascript)

```javascript
var semaphore = new Semaphore(10);

function niceFetch(url) {
    return semaphore.acquire()
    .then(release => {
        return fetch(url)
        .then(result => {
            release();
            return result;
        });
    });
}
```

---
_Source: https://npm.io/package/await-semaphore · Machine-readable twin of the npm.io package page. Health data is recomputed on every publish._