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Mark trees that need propagation in readContext
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Instead of storing matched context consumers in a Set, we can mark
when a consumer receives an update inside `readContext`.

I hesistated to put anything in this function because it's such a hot
path, but so are bail outs. Fortunately, we only need to set this flag
once, the first time a context is read. So I think it's a reasonable
trade off.

In exchange, propagation is faster because we no longer need to
accumulate a Set of matched consumers, and fiber bailouts are faster
because we don't need to consult that Set. And the code is simpler.
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@acdlite
acdlite committed Mar 2, 2021
1 parent 8ff5593 commit d1bfb29
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Showing 5 changed files with 100 additions and 185 deletions.
47 changes: 24 additions & 23 deletions packages/react-reconciler/src/ReactFiberFlags.js
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Original file line number Diff line number Diff line change
Expand Up @@ -12,50 +12,51 @@ import {enableCreateEventHandleAPI} from 'shared/ReactFeatureFlags';
export type Flags = number;

// Don't change these two values. They're used by React Dev Tools.
export const NoFlags = /* */ 0b000000000000000000000;
export const PerformedWork = /* */ 0b000000000000000000001;
export const NoFlags = /* */ 0b0000000000000000000000;
export const PerformedWork = /* */ 0b0000000000000000000001;

// You can change the rest (and add more).
export const Placement = /* */ 0b000000000000000000010;
export const Update = /* */ 0b000000000000000000100;
export const Placement = /* */ 0b0000000000000000000010;
export const Update = /* */ 0b0000000000000000000100;
export const PlacementAndUpdate = /* */ Placement | Update;
export const Deletion = /* */ 0b000000000000000001000;
export const ChildDeletion = /* */ 0b000000000000000010000;
export const ContentReset = /* */ 0b000000000000000100000;
export const Callback = /* */ 0b000000000000001000000;
export const DidCapture = /* */ 0b000000000000010000000;
export const Ref = /* */ 0b000000000000100000000;
export const Snapshot = /* */ 0b000000000001000000000;
export const Passive = /* */ 0b000000000010000000000;
export const Hydrating = /* */ 0b000000000100000000000;
export const Deletion = /* */ 0b0000000000000000001000;
export const ChildDeletion = /* */ 0b0000000000000000010000;
export const ContentReset = /* */ 0b0000000000000000100000;
export const Callback = /* */ 0b0000000000000001000000;
export const DidCapture = /* */ 0b0000000000000010000000;
export const Ref = /* */ 0b0000000000000100000000;
export const Snapshot = /* */ 0b0000000000001000000000;
export const Passive = /* */ 0b0000000000010000000000;
export const Hydrating = /* */ 0b0000000000100000000000;
export const HydratingAndUpdate = /* */ Hydrating | Update;
export const Visibility = /* */ 0b000000001000000000000;
export const Visibility = /* */ 0b0000000001000000000000;

export const LifecycleEffectMask = Passive | Update | Callback | Ref | Snapshot;

// Union of all commit flags (flags with the lifetime of a particular commit)
export const HostEffectMask = /* */ 0b000000001111111111111;
export const HostEffectMask = /* */ 0b0000000001111111111111;

// These are not really side effects, but we still reuse this field.
export const Incomplete = /* */ 0b000000010000000000000;
export const ShouldCapture = /* */ 0b000000100000000000000;
export const Incomplete = /* */ 0b0000000010000000000000;
export const ShouldCapture = /* */ 0b0000000100000000000000;
// TODO (effects) Remove this bit once the new reconciler is synced to the old.
export const PassiveUnmountPendingDev = /* */ 0b000001000000000000000;
export const ForceUpdateForLegacySuspense = /* */ 0b000010000000000000000;
export const DidPropagateContext = /* */ 0b000100000000000000000;
export const PassiveUnmountPendingDev = /* */ 0b0000001000000000000000;
export const ForceUpdateForLegacySuspense = /* */ 0b0000010000000000000000;
export const DidPropagateContext = /* */ 0b0000100000000000000000;
export const NeedsPropagation = /* */ 0b0001000000000000000000;

// Static tags describe aspects of a fiber that are not specific to a render,
// e.g. a fiber uses a passive effect (even if there are no updates on this particular render).
// This enables us to defer more work in the unmount case,
// since we can defer traversing the tree during layout to look for Passive effects,
// and instead rely on the static flag as a signal that there may be cleanup work.
export const PassiveStatic = /* */ 0b001000000000000000000;
export const PassiveStatic = /* */ 0b0010000000000000000000;

// These flags allow us to traverse to fibers that have effects on mount
// without traversing the entire tree after every commit for
// double invoking
export const MountLayoutDev = /* */ 0b010000000000000000000;
export const MountPassiveDev = /* */ 0b100000000000000000000;
export const MountLayoutDev = /* */ 0b0100000000000000000000;
export const MountPassiveDev = /* */ 0b1000000000000000000000;

// Groups of flags that are used in the commit phase to skip over trees that
// don't contain effects, by checking subtreeFlags.
Expand Down
112 changes: 37 additions & 75 deletions packages/react-reconciler/src/ReactFiberNewContext.new.js
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Original file line number Diff line number Diff line change
Expand Up @@ -33,7 +33,11 @@ import {
mergeLanes,
pickArbitraryLane,
} from './ReactFiberLane.new';
import {NoFlags, DidPropagateContext} from './ReactFiberFlags';
import {
NoFlags,
DidPropagateContext,
NeedsPropagation,
} from './ReactFiberFlags';

import invariant from 'shared/invariant';
import is from 'shared/objectIs';
Expand Down Expand Up @@ -409,14 +413,6 @@ function propagateContextChanges<T>(
// visit them during render. We should continue propagating the
// siblings, though
nextFiber = null;

// Keep track of subtrees whose propagation we deferred
if (deferredPropagation === null) {
deferredPropagation = new Set([consumer]);
} else {
deferredPropagation.add(consumer);
}
nextFiber = null;
}

// Since we already found a match, we can stop traversing the
Expand Down Expand Up @@ -513,29 +509,14 @@ export function propagateParentContextChangesToDeferredTree(
);
}

// Used by lazy context propagation algorithm. When we find a context dependency
// match, we don't propagate the changes any further into that fiber's subtree.
// We add the matched fibers to this set. Later, if something inside that
// subtree bails out of rendering, the presence of a parent fiber in this Set
// tells us that we need to continue propagating.
//
// This is a set of _current_ fibers, not work-in-progress fibers. That's why
// it's a set instead of a flag on the fiber.
let deferredPropagation: Set<Fiber> | null = null;

export function resetDeferredContextPropagation() {
// This is called by prepareFreshStack
deferredPropagation = null;
}

function propagateParentContextChanges(
current: Fiber,
workInProgress: Fiber,
renderLanes: Lanes,
forcePropagateEntireTree: boolean,
) {
if (!enableLazyContextPropagation) {
return false;
return;
}

// Collect all the parent providers that changed. Since this is usually small
Expand All @@ -544,58 +525,36 @@ function propagateParentContextChanges(
let parent = workInProgress;
let isInsidePropagationBailout = false;
while (parent !== null) {
const currentParent = parent.alternate;
invariant(
currentParent !== null,
'Should have a current fiber. This is a bug in React.',
);

if (!isInsidePropagationBailout) {
if (deferredPropagation === null) {
if ((parent.flags & DidPropagateContext) !== NoFlags) {
break;
}
} else {
if (currentParent !== null && deferredPropagation.has(currentParent)) {
// We're inside a subtree that previously bailed out of propagation.
// We must disregard the the DidPropagateContext flag as we continue
// searching for parent providers.
isInsidePropagationBailout = true;
// We know that none of the providers in between the propagation
// bailout and the nearest render bailout above that could have
// changed. So we can skip those.
do {
parent = parent.return;
invariant(
parent !== null,
'Expected to find a bailed out fiber. This is a bug in React.',
);
} while ((parent.flags & DidPropagateContext) === NoFlags);
} else if ((parent.flags & DidPropagateContext) !== NoFlags) {
break;
}
if ((parent.flags & NeedsPropagation) !== NoFlags) {
isInsidePropagationBailout = true;
} else if ((parent.flags & DidPropagateContext) !== NoFlags) {
break;
}
}

if (parent.tag === ContextProvider) {
if (currentParent !== null) {
const oldProps = currentParent.memoizedProps;
if (oldProps !== null) {
const providerType: ReactProviderType<any> = parent.type;
const context: ReactContext<any> = providerType._context;

const newProps = parent.pendingProps;
const newValue = newProps.value;

const oldValue = oldProps.value;

const changedBits = calculateChangedBits(context, newValue, oldValue);
if (changedBits !== 0) {
if (contexts !== null) {
contexts.push(context, changedBits);
} else {
contexts = [context, changedBits];
}
const currentParent = parent.alternate;
invariant(
currentParent !== null,
'Should have a current fiber. This is a bug in React.',
);
const oldProps = currentParent.memoizedProps;
if (oldProps !== null) {
const providerType: ReactProviderType<any> = parent.type;
const context: ReactContext<any> = providerType._context;

const newProps = parent.pendingProps;
const newValue = newProps.value;

const oldValue = oldProps.value;

const changedBits = calculateChangedBits(context, newValue, oldValue);
if (changedBits !== 0) {
if (contexts !== null) {
contexts.push(context, changedBits);
} else {
contexts = [context, changedBits];
}
}
}
Expand Down Expand Up @@ -628,10 +587,10 @@ function propagateParentContextChanges(
//
// Unfortunately, though, we need to ignore this flag when we're inside a
// tree whose context propagation was deferred — that's what the
// `deferredPropagation` set is for.
// `NeedsPropagation` flag is for.
//
// If we could instead bail out before entering the siblings' beging phase,
// then we could remove both `DidPropagateContext` and `deferredPropagation`.
// If we could instead bail out before entering the siblings' begin phase,
// then we could remove both `DidPropagateContext` and `NeedsPropagation`.
// Consider this as part of the next refactor to the fiber tree structure.
workInProgress.flags |= DidPropagateContext;
}
Expand Down Expand Up @@ -750,6 +709,9 @@ export function readContext<T>(
// TODO: This is an old field. Delete it.
responders: null,
};
if (enableLazyContextPropagation) {
currentlyRenderingFiber.flags |= NeedsPropagation;
}
} else {
// Append a new context item.
lastContextDependency = lastContextDependency.next = contextItem;
Expand Down
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