a basic queue with concurrency
var Queue = require'basic-queue';var q = request concurrency / numWorkers;qadd;
q = Queue(callback, concurrency)
callback is the function that this queue runs. Concurrency is how
many simultaneous jobs should run of that function.
callback will receive
callback as arguments. If
callback is a call with an error as a first
argument, the queue will emit an error event.
Tell the queue to start a new job if it isn't over the concurrency limit.