Class: DelayQueue

DelayQueue

Queue of 'Delayed' items, item can only be taken when its delay has expired The head of the queue is that Delayed item whose delay expired furthest in the past. If no delay has expired there is no head and poll() will return null. Expiration occurs when the supplied delayFn(item) returns a value less than or equal to zero. Even though unexpired items cannot be removed using take() or poll(), they are otherwise treated as normal item. For example, the size method returns the count of both expired and unexpired items. This queue does not permit null items. This queue requires a delay function while construction Reference: DelayQueue in Oracle JDK

new DelayQueue(delayFn)

Example

var DelayQueue = require("dsjslib").DelayQueue
var dq=new DelayQueue(function(task){
    return task.schedule - Date.now();
})
Parameters:
Name Type Description
delayFn DelayQueue~userDelayFn

A user provided delay function
Source:

Extends

Methods

clear()

Cleanup and remove all elements from the queue

Inherited From:
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entries() → {Array}

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Returns:

Returns array of elements in the queue. Ordering of those elements in undefined

Type
Array

offer(obj) → {PriorityQueue}

Parameters:
Name Type Description
obj

Insert the object in queue. Re-heapifies the queue.
Inherited From:
Source:
Returns:

this

Type
PriorityQueue

peek() → {*}

Returns, without removing, the element at the head of the queue

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Returns:

Returns the element at the head of the queue . The head of this queue is the maximum element with respect to the specified ordering. If multiple elements are tied for max value, the head is one of those elements -- ties are broken arbitrarily.

Type
*

poll() → {*}

Returns and removes the element at the head of the queue . Re-heapifies the queue.. The head of this queue is the element whose delay expires furthest in the past if there is no such element with negative or zero expired delay, this method returns null

Source:
Returns:

Element whose delay expires furthest in the past

Type
*

size() → {Number}

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Returns:

number of elements in the queue

Type
Number

take(callback)

Retrieve and remove the head of queue when it expires. Unlike poll() which returns immediately with either null or the head element (if it has expired), this method registers the user callback which will be invoked when the an item is available i.e. delay has expired.

Parameters:
Name Type Description
callback DelayQueue~onAvailableCb
Source:

Type Definitions

onAvailableCb(err, item)

The callback is asynchronous and takes two arguments err and item err contains any error encountered and item is the head object once its available.

Parameters:
Name Type Description
err Error

if any, null otherwise
item *

head element once available
Source:

userDelayFn(queueElement)

A user provided delay function for ordering of elements in queue

Parameters:
Name Type Description
queueElement *
Source:
Returns:

The function should return a negative integer, zero, or a positive integer depending on how much time remains before the item is expired. The argument to the function is the item for which delay is being queried