This scheduler allows you to run multiple co "threads" that can yield and do async actions without being interrupted until explicitly declared.

co-scheduler.js

var co = require('co')

var scheduler = 
{
	queue : []
}

// Requests control from scheduler
scheduler.promote = function()
{
	if ( scheduler.asleep )
	{
		scheduler.asleep = false
		scheduler.resume() // wake up the scheduler
	}
	return new Promise( resolve => scheduler.queue.push( resolve ) )
}

// Releases control of scheduler
scheduler.surrender = function()
{
	scheduler.resume()
}

// Helper function to ensure the co "thread" requests control at the start, 
// and releases when its done
scheduler.co = function( gen )
{
	co( function*()
	{
		yield scheduler.promote()
		yield gen()
		scheduler.surrender()
	} )
}

// Sleeps a co "thread", without giving up control
scheduler.sleep(t) = function{
    return new Promise( resolve => setTimeout( resolve, t * 1000 ) )
}

// Sleeps a co "thread", allowing others to take control while it sleeps
scheduler.deepsleep = function*(t)
{
	scheduler.surrender() // Release control in preperation
	yield scheduler.sleep(t) // Go to sleep
	yield scheduler.promote() // Awake again, request control!
}

// Auto-start the scheduler thread
co ( function*()
{  
	while ( true )
	{
		var next = scheduler.queue.shift()
		if ( typeof next != 'undefined' )
			next()
		else
			scheduler.asleep = true

		yield new Promise( resolve => scheduler.resume = resolve )
	}
} )

module.exports = scheduler