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acdlite Memoize promise listeners to prevent exponential growth (#14429)
* Memoize promise listeners to prevent exponential growth

Previously, React would attach a new listener every time a promise is
thrown, regardless of whether the same listener was already attached
during a previous render. Because React attempts to render every time
a promise resolves, the number of listeners grows quickly.

This was especially bad in synchronous mode because the renders that
happen when the promise pings are not batched together. So if a single
promise has multiple listeners for the same root, there will be multiple
renders, which in turn results in more listeners being added to the
remaining unresolved promises. This results in exponential growth in
the number of listeners with respect to the number of IO-bound
components in a single render.

Fixes #14220

* Memoize on the root and Suspense fiber instead of on the promise

* Add TODO to fix persistent mode tests
Latest commit 4a10721 Dec 14, 2018


This is an experimental package for creating custom React renderers.

Its API is not as stable as that of React, React Native, or React DOM, and does not follow the common versioning scheme.

Use it at your own risk.


const Reconciler = require('react-reconciler');

const HostConfig = {
  // You'll need to implement some methods here.
  // See below for more information and examples.

const MyRenderer = Reconciler(HostConfig);

const RendererPublicAPI = {
  render(element, container, callback) {
    // Call MyRenderer.updateContainer() to schedule changes on the roots.
    // See ReactDOM, React Native, or React ART for practical examples.

module.exports = RendererPublicAPI;

Practical Examples

A "host config" is an object that you need to provide, and that describes how to make something happen in the "host" environment (e.g. DOM, canvas, console, or whatever your rendering target is). It looks like this:

const HostConfig = {
  createInstance(type, props) {
    // e.g. DOM renderer returns a DOM node
  // ...
  supportsMutation: true, // it works by mutating nodes
  appendChild(parent, child) {
    // e.g. DOM renderer would call .appendChild() here
  // ...

For an introduction to writing a very simple custom renderer, check out this article series:

The full list of supported methods can be found here. For their signatures, we recommend looking at specific examples below.

The React repository includes several renderers. Each of them has its own host config.

The examples in the React repository are declared a bit differently than a third-party renderer would be. In particular, the HostConfig object mentioned above is never explicitly declared, and instead is a module in our code. However, its exports correspond directly to properties on a HostConfig object you'd need to declare in your code:

If these links break please file an issue and we’ll fix them. They intentionally link to the latest versions since the API is still evolving. If you have more questions please file an issue and we’ll try to help!