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Mount/unmount passive effects when Offscreen visibility changes (#24977)
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* Remove unnecessary try-catch from passive deletion

The individual unmount calls are already wrapped in a catch block, so
this outer one serves no purpose.

* Extract passive unmount effects to separate functions
    
I'm about to add a "disconnect passive effects" function that will share
much of the same code as commitPassiveUnmountOnFiber. To minimize the
duplicated code, I've extracted the shared parts into separate
functions, similar to what I did for commitLayoutEffectOnFiber and
reappearLayoutEffects.

This may not save much on code size because Closure will likely inline
some of it, anyway, but it makes it harder for the two paths to
accidentally diverge.

* Mount/unmount passive effects on hide/show

This changes the behavior of Offscreen so that passive effects are
unmounted when the tree is hidden, and re-mounted when the tree is
revealed again. This is already how layout effects worked.

In the future we will likely add an option or heuristic to only unmount
the effects of a hidden tree after a delay. That way if the tree quickly
switches back to visible, we can skip toggling the effects entirely.

This change does not apply to suspended trees, which happen to use
the Offscreen fiber type as an implementation detail. Passive effects
remain mounted while the tree is suspended, for the reason described
above — it's likely that the suspended tree will resolve and switch
back to visible within a short time span.

At a high level, what this capability enables is a feature we refer to
as "resuable state". The real value proposition here isn't so much the
behavior of effects — it's that you can switch back to a previously
rendered tree without losing the state of the UI.

* Add more coverage for nested Offscreen cases
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@acdlite
acdlite authored Jul 29, 2022
1 parent 4ea064e commit 80f3d88
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Showing 5 changed files with 616 additions and 177 deletions.
240 changes: 161 additions & 79 deletions packages/react-reconciler/src/ReactFiberCommitWork.new.js
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Original file line number Diff line number Diff line change
Expand Up @@ -3553,6 +3553,60 @@ export function commitPassiveUnmountEffects(finishedWork: Fiber): void {
resetCurrentDebugFiberInDEV();
}

function detachAlternateSiblings(parentFiber: Fiber) {
if (deletedTreeCleanUpLevel >= 1) {
// A fiber was deleted from this parent fiber, but it's still part of the
// previous (alternate) parent fiber's list of children. Because children
// are a linked list, an earlier sibling that's still alive will be
// connected to the deleted fiber via its `alternate`:
//
// live fiber --alternate--> previous live fiber --sibling--> deleted
// fiber
//
// We can't disconnect `alternate` on nodes that haven't been deleted yet,
// but we can disconnect the `sibling` and `child` pointers.

const previousFiber = parentFiber.alternate;
if (previousFiber !== null) {
let detachedChild = previousFiber.child;
if (detachedChild !== null) {
previousFiber.child = null;
do {
const detachedSibling = detachedChild.sibling;
detachedChild.sibling = null;
detachedChild = detachedSibling;
} while (detachedChild !== null);
}
}
}
}

function commitHookPassiveUnmountEffects(
finishedWork: Fiber,
nearestMountedAncestor,
hookFlags: HookFlags,
) {
if (
enableProfilerTimer &&
enableProfilerCommitHooks &&
finishedWork.mode & ProfileMode
) {
startPassiveEffectTimer();
commitHookEffectListUnmount(
hookFlags,
finishedWork,
nearestMountedAncestor,
);
recordPassiveEffectDuration(finishedWork);
} else {
commitHookEffectListUnmount(
hookFlags,
finishedWork,
nearestMountedAncestor,
);
}
}

function recursivelyTraversePassiveUnmountEffects(parentFiber: Fiber): void {
// Deletions effects can be scheduled on any fiber type. They need to happen
// before the children effects have fired.
Expand All @@ -3562,44 +3616,15 @@ function recursivelyTraversePassiveUnmountEffects(parentFiber: Fiber): void {
if (deletions !== null) {
for (let i = 0; i < deletions.length; i++) {
const childToDelete = deletions[i];
try {
// TODO: Convert this to use recursion
nextEffect = childToDelete;
commitPassiveUnmountEffectsInsideOfDeletedTree_begin(
childToDelete,
parentFiber,
);
} catch (error) {
captureCommitPhaseError(childToDelete, parentFiber, error);
}
}
}

if (deletedTreeCleanUpLevel >= 1) {
// A fiber was deleted from this parent fiber, but it's still part of
// the previous (alternate) parent fiber's list of children. Because
// children are a linked list, an earlier sibling that's still alive
// will be connected to the deleted fiber via its `alternate`:
//
// live fiber
// --alternate--> previous live fiber
// --sibling--> deleted fiber
//
// We can't disconnect `alternate` on nodes that haven't been deleted
// yet, but we can disconnect the `sibling` and `child` pointers.
const previousFiber = parentFiber.alternate;
if (previousFiber !== null) {
let detachedChild = previousFiber.child;
if (detachedChild !== null) {
previousFiber.child = null;
do {
const detachedSibling = detachedChild.sibling;
detachedChild.sibling = null;
detachedChild = detachedSibling;
} while (detachedChild !== null);
}
// TODO: Convert this to use recursion
nextEffect = childToDelete;
commitPassiveUnmountEffectsInsideOfDeletedTree_begin(
childToDelete,
parentFiber,
);
}
}
detachAlternateSiblings(parentFiber);
}

const prevDebugFiber = getCurrentDebugFiberInDEV();
Expand All @@ -3622,40 +3647,111 @@ function commitPassiveUnmountOnFiber(finishedWork: Fiber): void {
case SimpleMemoComponent: {
recursivelyTraversePassiveUnmountEffects(finishedWork);
if (finishedWork.flags & Passive) {
if (
enableProfilerTimer &&
enableProfilerCommitHooks &&
finishedWork.mode & ProfileMode
) {
startPassiveEffectTimer();
commitHookEffectListUnmount(
HookPassive | HookHasEffect,
finishedWork,
finishedWork.return,
);
recordPassiveEffectDuration(finishedWork);
} else {
commitHookEffectListUnmount(
HookPassive | HookHasEffect,
finishedWork,
finishedWork.return,
);
}
commitHookPassiveUnmountEffects(
finishedWork,
finishedWork.return,
HookPassive | HookHasEffect,
);
}
break;
}
// TODO: Disconnect passive effects when a tree is hidden, perhaps after
// a delay.
// case OffscreenComponent: {
// ...
// }
case OffscreenComponent: {
const instance: OffscreenInstance = finishedWork.stateNode;
const nextState: OffscreenState | null = finishedWork.memoizedState;

const isHidden = nextState !== null;

if (
isHidden &&
instance.visibility & OffscreenPassiveEffectsConnected &&
// For backwards compatibility, don't unmount when a tree suspends. In
// the future we may change this to unmount after a delay.
(finishedWork.return === null ||
finishedWork.return.tag !== SuspenseComponent)
) {
// The effects are currently connected. Disconnect them.
// TODO: Add option or heuristic to delay before disconnecting the
// effects. Then if the tree reappears before the delay has elapsed, we
// can skip toggling the effects entirely.
instance.visibility &= ~OffscreenPassiveEffectsConnected;
recursivelyTraverseDisconnectPassiveEffects(finishedWork);
} else {
recursivelyTraversePassiveUnmountEffects(finishedWork);
}

break;
}
default: {
recursivelyTraversePassiveUnmountEffects(finishedWork);
break;
}
}
}

function recursivelyTraverseDisconnectPassiveEffects(parentFiber: Fiber): void {
// Deletions effects can be scheduled on any fiber type. They need to happen
// before the children effects have fired.
const deletions = parentFiber.deletions;

if ((parentFiber.flags & ChildDeletion) !== NoFlags) {
if (deletions !== null) {
for (let i = 0; i < deletions.length; i++) {
const childToDelete = deletions[i];
// TODO: Convert this to use recursion
nextEffect = childToDelete;
commitPassiveUnmountEffectsInsideOfDeletedTree_begin(
childToDelete,
parentFiber,
);
}
}
detachAlternateSiblings(parentFiber);
}

const prevDebugFiber = getCurrentDebugFiberInDEV();
// TODO: Check PassiveStatic flag
let child = parentFiber.child;
while (child !== null) {
setCurrentDebugFiberInDEV(child);
disconnectPassiveEffect(child);
child = child.sibling;
}
setCurrentDebugFiberInDEV(prevDebugFiber);
}

function disconnectPassiveEffect(finishedWork: Fiber): void {
switch (finishedWork.tag) {
case FunctionComponent:
case ForwardRef:
case SimpleMemoComponent: {
// TODO: Check PassiveStatic flag
commitHookPassiveUnmountEffects(
finishedWork,
finishedWork.return,
HookPassive,
);
// When disconnecting passive effects, we fire the effects in the same
// order as during a deletiong: parent before child
recursivelyTraverseDisconnectPassiveEffects(finishedWork);
break;
}
case OffscreenComponent: {
const instance: OffscreenInstance = finishedWork.stateNode;
if (instance.visibility & OffscreenPassiveEffectsConnected) {
instance.visibility &= ~OffscreenPassiveEffectsConnected;
recursivelyTraverseDisconnectPassiveEffects(finishedWork);
} else {
// The effects are already disconnected.
}
break;
}
default: {
recursivelyTraverseDisconnectPassiveEffects(finishedWork);
break;
}
}
}

function commitPassiveUnmountEffectsInsideOfDeletedTree_begin(
deletedSubtreeRoot: Fiber,
nearestMountedAncestor: Fiber | null,
Expand Down Expand Up @@ -3728,25 +3824,11 @@ function commitPassiveUnmountInsideDeletedTreeOnFiber(
case FunctionComponent:
case ForwardRef:
case SimpleMemoComponent: {
if (
enableProfilerTimer &&
enableProfilerCommitHooks &&
current.mode & ProfileMode
) {
startPassiveEffectTimer();
commitHookEffectListUnmount(
HookPassive,
current,
nearestMountedAncestor,
);
recordPassiveEffectDuration(current);
} else {
commitHookEffectListUnmount(
HookPassive,
current,
nearestMountedAncestor,
);
}
commitHookPassiveUnmountEffects(
current,
nearestMountedAncestor,
HookPassive,
);
break;
}
// TODO: run passive unmount effects when unmounting a root.
Expand Down
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