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Core: Add "state reconciliation" to commit phase, pre-layout
Summary: This implements proposal #2 in our State architecture doc: https://fb.quip.com/bm2EAVwL7jQ5 Problem description: see the text in the comment of TreeStateReconciliation.h Solution: see also comments in TreeStateReconciliation.h. Changelog: [internal] Reviewed By: mdvacca Differential Revision: D19617329 fbshipit-source-id: 845fb5fe27f2591be433b6d77799707b3516fb1a
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,97 @@ | ||
| /* | ||
| * Copyright (c) Facebook, Inc. and its affiliates. | ||
| * | ||
| * This source code is licensed under the MIT license found in the | ||
| * LICENSE file in the root directory of this source tree. | ||
| */ | ||
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| #include "TreeStateReconciliation.h" | ||
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| namespace facebook { | ||
| namespace react { | ||
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| using ChangedShadowNodePairs = | ||
| std::vector<std::pair<SharedShadowNode, UnsharedShadowNode>>; | ||
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| /** | ||
| * Clones any children in the subtree that need to be cloned, and adds those to | ||
| * the `changedPairs` vector argument. | ||
| * | ||
| * @param parent | ||
| * @param newChildren | ||
| * @param oldChildren | ||
| * @param changedPairs | ||
| */ | ||
| static void reconcileStateWithChildren( | ||
| ShadowNode const *parent, | ||
| const SharedShadowNodeList &newChildren, | ||
| const SharedShadowNodeList &oldChildren, | ||
| ChangedShadowNodePairs &changedPairs) { | ||
| // Find children that are the same family in both trees. | ||
| // We only want to find nodes that existing in the new tree - if they | ||
| // don't exist in the new tree, they're being deleted; if they don't exist | ||
| // in the old tree, they're new. We don't need to deal with either of those | ||
| // cases here. | ||
| // Currently we use a naive double loop - this could be improved, but we need | ||
| // to be able to handle cases where nodes are entirely reordered, for | ||
| // instance. | ||
| for (int i = 0; i < newChildren.size(); i++) { | ||
| bool found = false; | ||
| for (int j = 0; j < oldChildren.size() && !found; j++) { | ||
| if (ShadowNode::sameFamily(*newChildren[i], *oldChildren[j])) { | ||
| UnsharedShadowNode newChild = | ||
| reconcileStateWithTree(newChildren[i].get(), oldChildren[j]); | ||
| if (newChild != nullptr) { | ||
| changedPairs.push_back(std::make_pair(newChildren[i], newChild)); | ||
| } | ||
| found = true; | ||
| } | ||
| } | ||
| } | ||
| } | ||
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| UnsharedShadowNode reconcileStateWithTree( | ||
| ShadowNode const *newNode, | ||
| SharedShadowNode committedNode) { | ||
| // If the revisions on the node are the same, we can finish here. | ||
| // Subtrees are guaranteed to be identical at this point, too. | ||
| if (committedNode->getStateRevision() <= newNode->getStateRevision()) { | ||
| return nullptr; | ||
| } | ||
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| // If we got this fair, we're guaranteed that the state of 1) this node, | ||
| // and/or 2) some descendant node is out-of-date and must be reconciled. | ||
| // This requires traversing all children, and we must at *least* clone | ||
| // this node, whether or not we clone and update any children. | ||
| const auto &newChildren = newNode->getChildren(); | ||
| const auto &oldChildren = committedNode->getChildren(); | ||
| ChangedShadowNodePairs changedPairs; | ||
| reconcileStateWithChildren(newNode, newChildren, oldChildren, changedPairs); | ||
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| ShadowNode::SharedListOfShared clonedChildren = | ||
| ShadowNodeFragment::childrenPlaceholder(); | ||
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| // If any children were cloned, we need to recreate the child list. | ||
| // This won't cause any children to be cloned that weren't already cloned - | ||
| // it just collects all children, cloned or uncloned, into a new list. | ||
| if (changedPairs.size() > 0) { | ||
| ShadowNode::UnsharedListOfShared newList = | ||
| std::make_shared<ShadowNode::ListOfShared>(); | ||
| for (int i = 0, j = 0; i < newChildren.size(); i++) { | ||
| if (j < changedPairs.size() && changedPairs[j].first == newChildren[i]) { | ||
| newList->push_back(changedPairs[j].second); | ||
| j++; | ||
| } else { | ||
| newList->push_back(newChildren[i]); | ||
| } | ||
| } | ||
| clonedChildren = newList; | ||
| } | ||
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| return newNode->clone({/* .props = */ ShadowNodeFragment::propsPlaceholder(), | ||
| /* .children = */ clonedChildren, | ||
| /* .state = */ newNode->getMostRecentState()}); | ||
| } | ||
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| } // namespace react | ||
| } // namespace facebook |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,33 @@ | ||
| /* | ||
| * Copyright (c) Facebook, Inc. and its affiliates. | ||
| * | ||
| * This source code is licensed under the MIT license found in the | ||
| * LICENSE file in the root directory of this source tree. | ||
| */ | ||
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| #include <react/core/ShadowNode.h> | ||
| #include <react/core/ShadowNodeFragment.h> | ||
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| namespace facebook { | ||
| namespace react { | ||
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| /** | ||
| * Problem Description: because of C++ State, the React Native C++ ShadowTree | ||
| * can diverge from the ReactJS ShadowTree; ReactJS communicates all tree | ||
| * changes to C++, but C++ state commits are not propagated to ReactJS (ReactJS | ||
| * may or may not clone nodes with state changes, but it has no way of knowing | ||
| * if it /should/ clone those nodes; so those clones may never happen). This | ||
| * causes a number of problems. This function resolves the problem by taking a | ||
| * candidate tree being committed, and sees if any State changes need to be | ||
| * applied to it. If any changes need to be made, a new ShadowNode is returned; | ||
| * otherwise, nullptr is returned if the node is already consistent with the | ||
| * latest tree, including all state changes. | ||
| * | ||
| * This should be called during the commit phase, pre-layout and pre-diff. | ||
| */ | ||
| UnsharedShadowNode reconcileStateWithTree( | ||
| ShadowNode const *newNode, | ||
| SharedShadowNode committedNode); | ||
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| } // namespace react | ||
| } // namespace facebook |