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RequestPool Manager

The RequestPool Manager has been extensively reworked to provide two new features: 1) asynchronous image retrieval and decoding 2) requests re-ordering.

ImageLoad and ImageRetrieval Queues

Previously, there was just one loading queue for fetching and decoding an image. Once the image decoding was completed, a new request was initiated. This had a constraint for when decoding required time; thus, no new retrieval (fetch) requests would be sent, even if additional requests were permitted based on the configured maximum number of requests.

To overcome this limitation, two distinct queues have been created for this purpose: imageRetrievalPoolManager and imageLoadPoolManager, each with their own configurable maximum concurrent jobs. They are separated and executed asynchronously from one another, allowing each retrieval request to be initiated instantly upon the availability of a request firing slot.

Splitting the image retrieval request and decoding is enabled by default Cornerstone-wado-image-loader version v4.0.0-rc or above.

// Loading = Retrieval + Decoding
imageLoadPoolManager.maxNumRequests = {
interaction: 1000,
thumbnail: 1000,
prefetch: 1000,

// Retrieval (usually) === XHR requests
imageRetrievalPoolManager.maxNumRequests = {
interaction: 20,
thumbnail: 20,
prefetch: 20,


In your custom imageLoader or volumeLoader, to properly use the poolManagers inside cornerstone, you need to define a sendRequest function to make an load image request.

import {
} from '@cornerstonejs/core';

function sendRequest(imageId, imageIdIndex, options) {
return loadAndCacheImage(imageId, options).then(
(image) => {
// render, image, imageIdIndex, imageId);
(error) => {, error, imageIdIndex, imageId);

const imageId = 'schema://image';
const imageIdIndex = 10;

const requestType = RequestType.Interaction;
const priority = -5;
const additionalDetails = { imageId };
const options = {
targetBuffer: {
type: 'Float32Array',

sendRequest.bind(this, imageId, imageIdIndex, options),

Requests re-ordering

You could have a certain sequence in mind for retrieving the images. For example, suppose you want to load a volume from the middle slice to the top and bottom. We have implemented such option in the cornerstoneStreamingImageVolumeLoader. You can read more about it in the re-ordering requests section.