Decouple update priority tracking from Scheduler package #19121

rickhanlonii · 2020-06-12T03:27:32Z

Summary

We'd like to remove a dependency on the Scheduler priority from React internals by replacing it with a currentLanePriority which will be tracked inside React. This PR starts currentLanePriority implementation by setting it everywhere that the scheduler priority is set, and then logging mismatches as they occur.

The next step is to investigate mismatches and handle them appropriately.

codesandbox-ci · 2020-06-12T03:31:24Z

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packages/react-reconciler/src/ReactFiberHooks.new.js

packages/react-reconciler/src/ReactFiberWorkLoop.new.js

sebmarkbage

We have way too many execution contexts. Scheduler, execution context, suspense config and now this. I think we need to take a step back and come up with a plan for how we get rid of the overhead. Like the existing runWithPriority with a new closure just to set one state is completely unacceptable overhead, so we shouldn't follow that lead.

I understand that this is just one step along refactoring but I worry that we're refactoring to has too much inherent complexity.

Do we have a plan for what we want to do with 1) execution context, 2) runWithPriority and 3) how we can avoid special cases like priorityLevel < UserBlockingPriority all over the code base?

(this is more of a comment to @acdlite ofc :) )

sebmarkbage · 2020-06-12T05:51:28Z

For perspective the way I look at setState is that in an optimal reactive system it's essentially this:

setState = (reducer) => {
  inst.nextState = reducer(inst.nextState);
  if (!inst.isDirty) {
    inst.isDirty = true;
    dirtyInstances.push(inst);
  }
}

The goal is to get close to this, because if we're not close then the system doesn't pay for itself, but we're very far away from this for a simple state change atm. I think we might need to do something more radical.

acdlite · 2020-06-12T16:07:15Z

Do we have a plan for what we want to do with 1) execution context, 2) runWithPriority and 3) how we can avoid special cases like priorityLevel < UserBlockingPriority all over the code base?

This PR is meant to address 2 and 3. It doesn't in the current state but that's one of the goals.

acdlite · 2020-06-12T16:40:24Z

I think we agree on the final end state. The goals for this first step are a bit confusing and contradictory so I'll list them here:

The main goal is to decouple the Scheduler priority from React update priority. It should be possible for us to control the priority of updates without going through Scheduler. This helps not only with coupling, but also means (in the future) we can avoid the overhead of runWithPriority. All of our APIs that change the priority already have a try/finally block; we can mutate the current update priority directly without a wrapper function.
We can't remove runWithPriority entirely without a semantic change. So in this first step, we'll keep all the existing runWithPriority calls. We'll start removing them behind the feature flag Rick has added (could maybe move that to a separate PR).
Similarly, we need to keep the getCurrentPriorityLevel check at the end of the requestUpdateLane algorithm so that outside runWithPriority calls still affect update priority.

Once the decoupling is complete, then we can move on to actually removing the extra wrappers. This will require some semantic changes and we'll need to audit www for existing uses.

packages/react-reconciler/src/ReactFiberHooks.new.js

packages/react-reconciler/src/ReactFiberHooks.old.js

packages/react-reconciler/src/ReactFiberLane.js

packages/react-reconciler/src/ReactFiberWorkLoop.new.js

acdlite · 2020-06-12T16:57:00Z

This is a really great first React PR!

acdlite · 2020-06-12T16:57:39Z

Sorry, I guess I mean first reconciler PR. I know it's not your first React PR ever :D

packages/shared/ReactFeatureFlags.js

sizebot · 2020-06-16T00:54:58Z

Details of bundled changes.

Comparing: c3e42a9...4294152

react-dom

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react-reconciler

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Size changes (experimental)

Generated by 🚫 dangerJS against 4294152

sizebot · 2020-06-16T00:58:21Z

Details of bundled changes.

Comparing: c3e42a9...4294152

react-dom

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react-reconciler

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Size changes (stable)

Generated by 🚫 dangerJS against 4294152

packages/react-reconciler/src/ReactFiberHooks.new.js

packages/react-reconciler/src/__tests__/ReactIncrementalUpdates-test.js

packages/react-reconciler/src/ReactFiberWorkLoop.new.js

packages/react-dom/src/events/ReactDOMEventReplaying.js

packages/react-dom/src/client/ReactDOM.js

packages/react-dom/src/events/ReactDOMEventReplaying.js

packages/shared/ReactFeatureFlags.js

rickhanlonii · 2020-06-26T05:09:29Z

Published for review, this should be good to go now 👍

facebook-github-bot added the CLA Signed label Jun 12, 2020

rickhanlonii commented Jun 12, 2020

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sebmarkbage reviewed Jun 12, 2020

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