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

$3

Create a new semaphore with the given count.

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

var semaphore = new Semaphore(10);
`

$3

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();
});
});
`

$3

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

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

$3

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.

$3

`typescript
var semaphore = new Semaphore(10);

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

$3

`javascript
var semaphore = new Semaphore(10);

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

$3

`javascript
var semaphore = new Semaphore(10);

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