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React?Fiber構(gòu)建源碼解析_React

作者：GW_劉振 ? 更新時間： 2023-04-07 編程語言

引言

前面的章節(jié)，我們在render方法里，簡單涉及到了fiber，那么：

  • fiber究竟是什么？
  • fiber的出現(xiàn)解決了什么問題？
  • 為什么fiber之前的版本，沒辦法解決

下面，我們帶著這些問題，來仔細(xì)聊聊Fiber

一. Fiber是什么

在fiber出現(xiàn)之前，react的架構(gòu)體系只有協(xié)調(diào)器reconciler和渲染器render。

當(dāng)前有新的update時，react會遞歸所有的vdom節(jié)點(diǎn)，如果dom節(jié)點(diǎn)過多，會導(dǎo)致其他事件影響滯后，造成卡頓。即之前的react版本無法中斷工作過程，一旦遞歸開始無法停留下來。

為了解決這一系列問題，react歷時多年重構(gòu)了底層架構(gòu)，引入了fiber。 fiber的出現(xiàn)使得react能夠異步可中斷工作任務(wù)，并且可以在瀏覽器空閑時，從中斷處繼續(xù)往下工作。 當(dāng)出現(xiàn)多個高優(yōu)先任務(wù)并行時，react引入lane模型取代之前的expireTime機(jī)制。

這里提及下vue工作原理，為什么有新的update任務(wù)時，vue不需要做全量遞歸，而react需要？（留個懸念，大家可以先思考下）

fiber本質(zhì)上是一種數(shù)據(jù)結(jié)構(gòu)，在react17后，沒有vdom概念，一切皆是Fiber，但Fiber != vdom。

二. FiberRoot

FiberRoot是react啟動階段，要構(gòu)建的fiber對象。與之容易混淆是rootFiber，下面會具體介紹。

fiberRoot生成

  function createFiberRoot(containerInfo, tag, hydrate, hydrationCallbacks) {
    var root = new FiberRootNode(containerInfo, tag, hydrate);
    // stateNode is any.
    var uninitializedFiber = createHostRootFiber(tag);
    root.current = uninitializedFiber;
    uninitializedFiber.stateNode = root;
    initializeUpdateQueue(uninitializedFiber);
    return root;
  }

fiberRoot類

function FiberRootNode(containerInfo, tag, hydrate) {
    this.tag = tag;
    this.containerInfo = containerInfo;
    this.pendingChildren = null;
    this.current = null;
    this.pingCache = null;
    this.finishedWork = null;
    this.timeoutHandle = noTimeout;
    this.context = null;
    this.pendingContext = null;
    this.hydrate = hydrate;
    this.callbackNode = null;
    this.callbackPriority = NoLanePriority;
    this.eventTimes = createLaneMap(NoLanes);
    this.expirationTimes = createLaneMap(NoTimestamp);
    this.pendingLanes = NoLanes;
    this.suspendedLanes = NoLanes;
    this.pingedLanes = NoLanes;
    this.expiredLanes = NoLanes;
    this.mutableReadLanes = NoLanes;
    this.finishedLanes = NoLanes;
    this.entangledLanes = NoLanes;
    this.entanglements = createLaneMap(NoLanes);
    {
      this.mutableSourceEagerHydrationData = null;
    }
    {
      this.interactionThreadID = unstable_getThreadID();
      this.memoizedInteractions = new Set();
      this.pendingInteractionMap = new Map();
    }
    {
      switch (tag) {
        case BlockingRoot:
          this._debugRootType = 'createBlockingRoot()';
          break;
        case ConcurrentRoot:
          this._debugRootType = 'createRoot()';
          break;
        case LegacyRoot:
          this._debugRootType = 'createLegacyRoot()';
          break;
      }
    }
  }

fiberRoot本質(zhì)上fiber的頂層對象，其中tag記錄了幾種啟動模式：

  • 0普通模式
  • 1 小部分并發(fā)模式
  • 2 并發(fā)模式

啟動模式的不同，在后協(xié)調(diào)階段有具體差異。

該類引用的實(shí)例，即current對象是rootFiber。finishedWork是fiber完成協(xié)調(diào)器work之后的結(jié)果，下面有許多字段都帶有l(wèi)ane，這里可以先不關(guān)注，后面章節(jié)我們單獨(dú)聊聊Lane模型

三. RootFiber

rootFiber生成

  function createFiberRoot(containerInfo, tag, hydrate, hydrationCallbacks) {
    var root = new FiberRootNode(containerInfo, tag, hydrate);
    // stateNode is any.
    var uninitializedFiber = createHostRootFiber(tag);
    root.current = uninitializedFiber;
    uninitializedFiber.stateNode = root;
    initializeUpdateQueue(uninitializedFiber);
    return root;
  }

createHostRootFiber

  function createHostRootFiber(tag) {
    var mode;
    if (tag === ConcurrentRoot) {
      mode = ConcurrentMode | BlockingMode | StrictMode;
    } else if (tag === BlockingRoot) {
      mode = BlockingMode | StrictMode;
    } else {
      mode = NoMode;
    }
    if ( isDevToolsPresent) {
      // Always collect profile timings when DevTools are present.
      // This enables DevTools to start capturing timing at any point–
      // Without some nodes in the tree having empty base times.
      mode |= ProfileMode;
    }
    return createFiber(HostRoot, null, null, mode);
  }

FiberNode

function FiberNode(tag, pendingProps, key, mode) {
    this.tag = tag;
    this.key = key;
    this.elementType = null;
    this.type = null;
    this.stateNode = null;
    this.return = null;
    this.child = null;
    this.sibling = null;
    this.index = 0;
    this.ref = null;
    this.pendingProps = pendingProps; 
    this.memoizedProps = null; 
    this.updateQueue = null; 
    this.memoizedState = null;  
    this.dependencies = null;
    this.mode = mode; // Effects
    this.flags = NoFlags;     
    this.nextEffect = null;  
    this.firstEffect = null; 
    this.lastEffect = null; 
    this.lanes = NoLanes;
    this.childLanes = NoLanes;
    this.alternate = null;
    {
      this.actualDuration = Number.NaN;
      this.actualStartTime = Number.NaN;
      this.selfBaseDuration = Number.NaN;
      this.treeBaseDuration = Number.NaN; // It's okay to replace the initial doubles with smis after initialization.
      this.actualDuration = 0;
      this.actualStartTime = -1;
      this.selfBaseDuration = 0;
      this.treeBaseDuration = 0;
    }
    {
      // This isn't directly used but is handy for debugging internals:
      this._debugID = debugCounter++;
      this._debugSource = null;
      this._debugOwner = null;
      this._debugNeedsRemount = false;
      this._debugHookTypes = null;
      if (!hasBadMapPolyfill && typeof Object.preventExtensions === 'function') {
        Object.preventExtensions(this);
      }
    }
  }

到這里，fiberNode是一個類，往下的所有dom都將實(shí)例化這個類。

這里的tag依舊是啟動模式，return是父節(jié)點(diǎn)fiber，child是子節(jié)點(diǎn)第一個fiber，sibling是兄弟節(jié)點(diǎn)的fiber。

另外，flags很重要，在后續(xù)work階段會大量使用，另外flags和lane都是二進(jìn)制數(shù)據(jù)對象，后面大量運(yùn)用位運(yùn)算。

effect對象，會在work loop階段生成，也就是副作用，比如我們寫的useEffect，都在work lopp階段被掛載。

每個fiber的stateNode指向具體實(shí)例節(jié)點(diǎn)。

flags

export type Flags = number;
export const NoFlags = /*                      */ 0b000000000000000000;
export const PerformedWork = /*                */ 0b000000000000000001;
export const Placement = /*                    */ 0b000000000000000010;
export const Update = /*                       */ 0b000000000000000100;
export const PlacementAndUpdate = /*           */ 0b000000000000000110;
export const Deletion = /*                     */ 0b000000000000001000;
export const ContentReset = /*                 */ 0b000000000000010000;
export const Callback = /*                     */ 0b000000000000100000;
export const DidCapture = /*                   */ 0b000000000001000000;
export const Ref = /*                          */ 0b000000000010000000;
export const Snapshot = /*                     */ 0b000000000100000000;
export const Passive = /*                      */ 0b000000001000000000;
// TODO (effects) Remove this bit once the new reconciler is synced to the old.
export const PassiveUnmountPendingDev = /*     */ 0b000010000000000000;
export const Hydrating = /*                    */ 0b000000010000000000;
export const HydratingAndUpdate = /*           */ 0b000000010000000100;
// Passive & Update & Callback & Ref & Snapshot
export const LifecycleEffectMask = /*          */ 0b000000001110100100;
// Union of all host effects
export const HostEffectMask = /*               */ 0b000000011111111111;
// These are not really side effects, but we still reuse this field.
export const Incomplete = /*                   */ 0b000000100000000000;
export const ShouldCapture = /*                */ 0b000001000000000000;
export const ForceUpdateForLegacySuspense = /* */ 0b000100000000000000;
export const PassiveStatic = /*                */ 0b001000000000000000;
export const BeforeMutationMask = /*           */ 0b000000001100001010;
export const MutationMask = /*                 */ 0b000000010010011110;
export const LayoutMask = /*                   */ 0b000000000010100100;
export const PassiveMask = /*                  */ 0b000000001000001000;
export const StaticMask = /*                   */ 0b001000000000000000;
export const MountLayoutDev = /*               */ 0b010000000000000000;
export const MountPassiveDev = /*              */ 0b100000000000000000;

lane

export const NoLanes: Lanes = /*                        */ 0b0000000000000000000000000000000;
export const NoLane: Lane = /*                          */ 0b0000000000000000000000000000000;
export const SyncLane: Lane = /*                        */ 0b0000000000000000000000000000001;
export const SyncBatchedLane: Lane = /*                 */ 0b0000000000000000000000000000010;
export const InputDiscreteHydrationLane: Lane = /*      */ 0b0000000000000000000000000000100;
const InputDiscreteLanes: Lanes = /*                    */ 0b0000000000000000000000000011000;
const InputContinuousHydrationLane: Lane = /*           */ 0b0000000000000000000000000100000;
const InputContinuousLanes: Lanes = /*                  */ 0b0000000000000000000000011000000;
export const DefaultHydrationLane: Lane = /*            */ 0b0000000000000000000000100000000;
export const DefaultLanes: Lanes = /*                   */ 0b0000000000000000000111000000000;
const TransitionHydrationLane: Lane = /*                */ 0b0000000000000000001000000000000;
const TransitionLanes: Lanes = /*                       */ 0b0000000001111111110000000000000;
const RetryLanes: Lanes = /*                            */ 0b0000011110000000000000000000000;
export const SomeRetryLane: Lanes = /*                  */ 0b0000010000000000000000000000000;
export const SelectiveHydrationLane: Lane = /*          */ 0b0000100000000000000000000000000;
const NonIdleLanes = /*                                 */ 0b0000111111111111111111111111111;
export const IdleHydrationLane: Lane = /*               */ 0b0001000000000000000000000000000;
const IdleLanes: Lanes = /*                             */ 0b0110000000000000000000000000000;
export const OffscreenLane: Lane = /*                   */ 0b1000000000000000000000000000000;

關(guān)于flags和lane，我們先有個感性認(rèn)知，后面章節(jié)單獨(dú)分析

initializeUpdateQueue

  function initializeUpdateQueue(fiber) {
    var queue = {
      baseState: fiber.memoizedState,
      firstBaseUpdate: null,
      lastBaseUpdate: null,
      shared: {
        pending: null
      },
      effects: null
    };
    fiber.updateQueue = queue;
  }

rootFiber上調(diào)用initializeUpdateQueue，初始化queue對象，這里僅僅是初始化對象而已，并不是許多文章說fiber加入更新隊(duì)列。fiber的更新隊(duì)列和這里沒有任何關(guān)系，fiber的更新隊(duì)列是后續(xù)schedule調(diào)度的task queue。

四. Root

root對象是legacyCreateRootFromDOMContainer方法的返回對象，這個對象是全局唯一，并貫穿了react后續(xù)的各階段計(jì)算。

至此，我們對應(yīng)fiber有個感性的認(rèn)知。另外需要說明的是，每個dom節(jié)點(diǎn)都是fiber，fiber通過return, child, sibling關(guān)聯(lián)其他fiber，本質(zhì)上fiber是個鏈表數(shù)據(jù)結(jié)構(gòu)，這一點(diǎn)和后續(xù)的effect數(shù)據(jù)結(jié)構(gòu)還是有區(qū)別的。

在root生成后，首次初始化應(yīng)用，將進(jìn)入核心updateContainer方法

updateContainer(children, fiberRoot, parentComponent, callback);

updateContainer

  function updateContainer(element, container, parentComponent, callback) {
      // ...省略eventTime和lane相關(guān)，后續(xù)單獨(dú)介紹
    var update = createUpdate(eventTime, lane); // Caution: React DevTools currently depends on this property
    // being called "element".
    update.payload = {
      element: element
    };
    callback = callback === undefined ? null : callback;
    if (callback !== null) {
      {
        if (typeof callback !== 'function') {
          error('render(...): Expected the last optional `callback` argument to be a ' + 'function. Instead received: %s.', callback);
        }
      }
      update.callback = callback;
    }
    enqueueUpdate(current$1, update);
    scheduleUpdateOnFiber(current$1, lane, eventTime);
    return lane;
  }

createUpdate

  function createUpdate(eventTime, lane) {
    var update = {
      eventTime: eventTime,
      lane: lane,
      tag: UpdateState,
      payload: null,
      callback: null,
      next: null
    };
    return update;
  }

  function enqueueUpdate(fiber, update) {
    var updateQueue = fiber.updateQueue;
    if (updateQueue === null) {
      // Only occurs if the fiber has been unmounted.
      return;
    }
    var sharedQueue = updateQueue.shared;
    var pending = sharedQueue.pending;
    if (pending === null) {
      // This is the first update. Create a circular list.
      update.next = update;
    } else {
      update.next = pending.next;
      pending.next = update;
    }
    sharedQueue.pending = update;
  }

在rootFiber上，創(chuàng)建更新對象，并掛載至enqueueUpdate上。

update對象上payload很重要，后面在協(xié)調(diào)階段-fiber樹構(gòu)建階段是重要的輸入。

update對象也是鏈表結(jié)構(gòu)，通過next關(guān)聯(lián)下一個update對象。

原文鏈接：https://juejin.cn/post/7195054942413914171

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