co-semaphore

Counted semaphore primitive for generator flow-control.

Installation

Node.js

co-semaphore is available through npm:

npm install co-semaphore

Example

"use strict";
 
var co = require('co');
var Semaphore = require('co-semaphore').Semaphore;
 
function rand() {
  return Math.floor(Math.random() * 10) * 100;
}
 
function *read(i, lock) {
  yield lock.acquire();
  console.log('start:', i);
  yield wait(rand());
  lock.release();
  console.log('end:', i);
  return i * 10;
}
 
co(function *main() {
  var lock = new Semaphore(3);
  var res = [];
 
  for (let i = 1; i < 11; i++) {
    res.push(read(i, lock));
  }
 
  console.log('res', yield res);
})();

Usage

A low-level counted semaphore lock.

• @param {Number} workers

.length

Get length of waiting queue.

• @return {Number} length

.acquired

Get the current number of workers; threads which have acquired the lock but not yet released it.

• @return {Number} acquisitions

.available

Get the current number of unassigned workers; count of threads which can immediately acquire access without being put in the waiting queue.

• @return {Number} available

.count

Get count of semaphore state.

• @return {Number} count

.acquire()

Acquire permission to access shared resources.

yield sem.acquire();

.release()

Notify release of access to shared resources to a single waiting .acquire().

• @return {Boolean} release signalled acquire

var hadListener = sem.release();

.flush()

Notify release of access to shared resources to all waiting .acquire()s.

• @return {Boolean} release signalled acquire

var hadListeners = sem.flush();

.lock()

Acquire access to shared resources with closure. Access will be acquired prior to invoking the closure and unlocked as the closure unwinds.

• @param {Generator} closure

var res = yield sem.lock(function*() {
  // do async work with lock owned
  yield wait(100);
  return { hello: 'universe' };
});

License

(The MIT License)

Copyright (c) 2014 Jake Luer [e-mail]

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.