co-condvar

Conditional variable primitive for generator flow-control.

Installation

Node.js

co-condvar is available through npm:

npm install co-condvar

Example

The best way to think of a condvar is like a blocking event emitter. The following demonstrates a solution to the producer/consumer problem using a single conditional variable and its associated lock.

In this example yield cv.wait() is invoked while a lock is acquired. Because the lock can only be owned by one "thread" at a time, this code looks like a deadlock scenario. However, when a conditional variable is waiting, it releases it's lock and yield cv.wait() will only resume once the lock has been re-acquired.

This example requires code that manages the lock manually. This can be managed automatically by using co-mutex instead.

var Condvar = require('co-condvar').Condvar;
 
var queue = [];
 
function *producer(cv) {
  var i = 0;
  while(true) {
    // acquire lock
    yield cv.lock.acquire();
    while (queue.length) yield cv.wait('shift');
 
    // async stuff
    yield wait(100);
    queue.push(i++);
 
    // signal and release
    cv.signal('push');
    cv.lock.release();
  }
}
 
function *consumer(cond) {
  while(true) {
    // acquire lock
    yield cv.lock.acquire();
    while (!queue.length) yield cv.wait('push');
 
    // async stuff
    yield wait(100);
    var item = queue.shift();
 
    // signal and release
    cv.signal('shift');
    cv.lock.release();
  }
}
 
co(function *main() {
  var cv = new Condvar();
 
  co(producer)(cv);
  co(consumer)(cv);
 
  yield wait(1000);
  process.exit();
})();

Usage

Conditional variable implementation for Mutex and RWLock. Can use stringed keys for multi-variable conditions so it can be used as a yield-able event emitter.

• @param {Semaphore} lock to drop on .wait(). optional.

.lock

Get the semaphore lock that will be dropped for each .wait().

• @return {Semaphore} lock

yield condvar.lock.acquire();

.wait(key)

Wait for signal on a given key. Key is optional. Yieldable.

• @param {String} key

while (!ready) yield condvar.wait('event');

.signal(key)

Signal that a condition has met. Will unlock only the next waiting for the given key.

• @param {String} key optional
• @return {Boolean} any receivers

var hadWaiting = condvar.signal('event');

.broadcast(key)

Broadcast that a condition has met. Will unlock all waiting for the given key.

• @param {String} key optional
• @return {Boolean} any receivers

var hadWaiting = condvar.broadcast('event');

License

(The MIT License)

Copyright (c) 2014 Jake Luer jake@alogicalparadox.com

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.