parallel-queue

Queue for parallel tasks that can cancel and is destoryable

Usage

var parallelQueue = require('parallel-queue')

var pq = parallelQueue(4, function (args, done) {
  setTimeout(done, args.wait)
})

pq.push({wait: 30000})

// Cancel all pending tasks, and invoke callback on all running tasks with error
pq.destroy()

API

var queue = parallelQueue(parallel, worker)

Create a queue that is limited to parallel concurrent workers. worker will be invoked with (task, next), where task is whatever is pushed onto the queue and next is a normal callback function, passed an optional error as the first argument and up to three return values from succeeding arguments. These arguments will be passed on to the done callback in push.

var cancel = queue.push(task, done)

Queue task and call cb when done. queue.push will return a function that you can invoke to cancel the task, which in turn will invoke cb with a Error with err.cancel === true. If the task has already started, there is no way to cancel it, and it will not release a slot in the queue until done. If the queue has been destroyed, tasks will not be queued and done will be invoked immediately with an error.

Note: The task will not be executed before the nextTick as to avoid the worker function from plugging the event loop. This means you can .push and cancel as many tasks as you want synchronously, also from within the callback.

Note 2: You can cancel a running task, but that does not mean the actual work done by the worker is stopped, just that the cb supplied to .push is removed from the queue and called with an Error. The slot in the queue will be released as soon as the running worker calls the supplied next callback.

queue.destroy([err])

Cancel all pending tasks, and call the callback of all running tasks with an error. If err is not given, the default error will be used (see above).

queue.parallel

Number of tasks that can run in parallel. This is read-only

queue.pending

Number of tasks pending in the queue. This is excluding the current task if accessed from within the worker function

queue.running

Number of tasks running in the queue. This is including the current task if accessed from within the worker function.

queue.destroyed

Boolean set after destroy has finished

Install

npm install parallel-queue

License

ISC