sema

Async semaphore for shared or exclusive execution of JavaScript functions.


``
npm install sema
`

`js
var sema = require('sema')
var s = sema()

// exclusive mode
s.acquire(function () {
...
doReadWrite(function (err) {
...
s.release()
})
})

// shared mode
s.acquire(sema.SHARED, function () {
...
doReadOnly(function (err) {
...
s.release()
})
})

`

API

$3

Creates a semaphore instance.

$3

Acquire semaphore. Defaults to exclusive mode. Setting mode sema.SHARED to acquire a shared mode.

Callback to asynchronous function fn when semaphore available.
Invoked immediately if semaphore is free or shared only. Otherwise pushed to the wait queue.

Returns a promise if no fn provided. However this yields a slight delay when acquiring, due to the nature of promise. If such timing is important then callback function should be used.

$3

Release semaphore.

Invokes function from the wait queue if queue is not empty.

$3

Returns mode constant, the current state of semaphore.

$3

* sema.FREE = null
* sema.SHARED = 1
* sema.EXCLUSIVE = 2
* sema.WAIT = 3`

License

MIT