sema

Async semaphore for shared or exclusive execution of JavaScript functions.

npm install sema

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

var s = sema()

Creates a semaphore instance.

s.acquire([mode], [fn])

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.

s.release()

Release semaphore.

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

s.mode()

Returns mode constant, the current state of semaphore.

Mode Constants

• sema.FREE = null
• sema.SHARED = 1
• sema.EXCLUSIVE = 2
• sema.WAIT = 3

License

MIT