Detailed explanation of the fiber architecture of React16.2

本文主要和大家分享React16.2的fiber架构详解，希望能帮助到大家。insertUpdateIntoFiber 会根据fiber的状态创建一个或两个列队对象，对象是长成这样的对象是长成这样的

//by 司徒正美， 加群：370262116 一起研究React与anujs
// https://github.com/RubyLouvre/anu 欢迎加star
function createUpdateQueue(baseState) {//我们现在是丢了一个null做传参
  var queue = {
    baseState: baseState,
    expirationTime: NoWork,//NoWork会被立即执行
    first: null,
    last: null,
    callbackList: null,
    hasForceUpdate: false,
    isInitialized: false
  };

  return queue;
}

scheduleWork是一个奇怪的方法，只是添加一下参数

 function scheduleWork(fiber, expirationTime) {
    return scheduleWorkImpl(fiber, expirationTime, false);
  }

scheduleWorkImpl的最开头有一个recordScheduleUpdate方法，用来记录调度器的执行状态，如注释所示，它现在相当于什么都没有做

function recordScheduleUpdate() {
  if (enableUserTimingAPI) {//全局变量，默认为true
    if (isCommitting) {//全局变量，默认为false, 没有进入分支
      hasScheduledUpdateInCurrentCommit = true;
    }
    //全局变量，默认为null，没有没有进入分支
    if (currentPhase !== null && currentPhase !== 'componentWillMount' && currentPhase !== 'componentWillReceiveProps') {
      hasScheduledUpdateInCurrentPhase = true;
    }
  }
}

scheduleWorkImpl的一些分支非常复杂，我们打一些断点

function computeExpirationForFiber(fiber) {
    var expirationTime = void 0;
    if (expirationContext !== NoWork) {
      // An explicit expiration context was set;
      expirationTime = expirationContext;
    } else if (isWorking) {
      if (isCommitting) {
        // Updates that occur during the commit phase should have sync priority
        // by default.
        expirationTime = Sync;
      } else {
        // Updates during the render phase should expire at the same time as
        // the work that is being rendered.
        expirationTime = nextRenderExpirationTime;
      }
    } else {
      // No explicit expiration context was set, and we're not currently
      // performing work. Calculate a new expiration time.
      if (useSyncScheduling && !(fiber.internalContextTag & AsyncUpdates)) {
        // This is a sync update
        console.log("expirationTime", Sync)
        expirationTime = Sync;//命中这里
      } else {
        // This is an async update
        expirationTime = computeAsyncExpiration();
      }
    }
    return expirationTime;
  }
    function checkRootNeedsClearing(root, fiber, expirationTime) {
    if (!isWorking && root === nextRoot && expirationTime < nextRenderExpirationTime) {
      console.log("checkRootNeedsClearing对nextRoot，nextUnitOfWork，nextRenderExpirationTime进行置空")
      // Restart the root from the top.
      if (nextUnitOfWork !== null) {
        // This is an interruption. (Used for performance tracking.)
        interruptedBy = fiber;
      }
      nextRoot = null;
      nextUnitOfWork = null;
      nextRenderExpirationTime = NoWork;
    }else{
      console.log("checkRootNeedsClearing就是想酱油")
    }
  }

function scheduleWorkImpl(fiber, expirationTime, isErrorRecovery) {
    recordScheduleUpdate();//现在什么也没做

    var node = fiber;
    while (node !== null) {
      // Walk the parent path to the root and update each node&#39;s
      // expiration time.
      if (node.expirationTime === NoWork || node.expirationTime > expirationTime) {
        node.expirationTime = expirationTime;//由于默认就是NoWork,因此会被重写 Sync
      }
      if (node.alternate !== null) {//这里进不去
        if (node.alternate.expirationTime === NoWork || node.alternate.expirationTime > expirationTime) {
          node.alternate.expirationTime = expirationTime;
        }
      }
      if (node['return'] === null) {
        if (node.tag === HostRoot) {//进入这里
          var root = node.stateNode;
          checkRootNeedsClearing(root, fiber, expirationTime);
          console.log("requestWork",root, expirationTime)
          requestWork(root, expirationTime);
          checkRootNeedsClearing(root, fiber, expirationTime);
        } else {
          return;
        }
      }
      node = node['return'];
    }
  }

输出如下

requestWork也很难理解，里面太多全局变量，觉得不是前端的人搞的。为了帮助理解，我们继续加日志

//by 司徒正美， 加群：370262116 一起研究React与anujs

 // requestWork is called by the scheduler whenever a root receives an update.
  // It's up to the renderer to call renderRoot at some point in the future.
  /*
只要root收到更新(update对象)，requestWork就会被调度程序调用。
渲染器在将来的某个时刻调用renderRoot。
  */
  function requestWork(root, expirationTime) {
    if (nestedUpdateCount > NESTED_UPDATE_LIMIT) {
      invariant_1(false, 'Maximum update depth exceeded. This can happen when a component repeatedly calls setState inside componentWillUpdate or componentDidUpdate. React limits the number of nested updates to prevent infinite loops.');
    }

    // Add the root to the schedule.
    // Check if this root is already part of the schedule.
    if (root.nextScheduledRoot === null) {
      // This root is not already scheduled. Add it.
      console.log("设置remainingExpirationTime",expirationTime)
      root.remainingExpirationTime = expirationTime;
      if (lastScheduledRoot === null) {
        console.log("设置firstScheduledRoot， lastScheduledRoot")
        firstScheduledRoot = lastScheduledRoot = root;
        root.nextScheduledRoot = root;
      } else {
        lastScheduledRoot.nextScheduledRoot = root;
        lastScheduledRoot = root;
        lastScheduledRoot.nextScheduledRoot = firstScheduledRoot;
      }
    } else {
      // This root is already scheduled, but its priority may have increased.
      var remainingExpirationTime = root.remainingExpirationTime;
      if (remainingExpirationTime === NoWork || expirationTime < remainingExpirationTime) {
        // Update the priority.
        root.remainingExpirationTime = expirationTime;
      }
    }

    if (isRendering) {
      // Prevent reentrancy. Remaining work will be scheduled at the end of
      // the currently rendering batch.
      return;
    }

    if (isBatchingUpdates) {
      // Flush work at the end of the batch.
      if (isUnbatchingUpdates) {
        // ...unless we&#39;re inside unbatchedUpdates, in which case we should
        // flush it now.
        nextFlushedRoot = root;
        nextFlushedExpirationTime = Sync;
        console.log("performWorkOnRoot")
        performWorkOnRoot(nextFlushedRoot, nextFlushedExpirationTime);
      }
      return;
    }

    // TODO: Get rid of Sync and use current time?
    if (expirationTime === Sync) {
      console.log("进入performWork")
      performWork(Sync, null);
    } else {
      scheduleCallbackWithExpiration(expirationTime);
    }
  }

从日志输出来看，requestWork只是修改了两个全局变量，然后进入performWork。这三个内部方法起名很有意思。scheduleWork意为打算工作，requestWork意为申请工作，performWork意为努力工作（正式上班）

function performWork(minExpirationTime, dl) {
    deadline = dl;

    // Keep working on roots until there's no more work, or until the we reach
    // the deadline.
    //这里会将root设置为highestPriorityRoot
    findHighestPriorityRoot();

    if (enableUserTimingAPI && deadline !== null) {
      var didExpire = nextFlushedExpirationTime < recalculateCurrentTime();
      console.log(didExpire)
      stopRequestCallbackTimer(didExpire);
    }

    while (nextFlushedRoot !== null 
      && nextFlushedExpirationTime !== NoWork 
      && (minExpirationTime === NoWork || nextFlushedExpirationTime <= minExpirationTime) 
      && !deadlineDidExpire) {
      console.log("performWorkOnRoot")
      performWorkOnRoot(highestPriorityRoot, nextFlushedExpirationTime);
      // Find the next highest priority work.
      findHighestPriorityRoot();
    }

    // We&#39;re done flushing work. Either we ran out of time in this callback,
    // or there&#39;s no more work left with sufficient priority.

    // If we&#39;re inside a callback, set this to false since we just completed it.
    if (deadline !== null) {
      callbackExpirationTime = NoWork;
      callbackID = -1;
    }
    // If there&#39;s work left over, schedule a new callback.
    if (nextFlushedExpirationTime !== NoWork) {
      console.log("scheduleCallbackWithExpiration")
      scheduleCallbackWithExpiration(nextFlushedExpirationTime);
    }

    // Clean-up.
    deadline = null;
    deadlineDidExpire = false;
    nestedUpdateCount = 0;

    if (hasUnhandledError) { //如果有没处理的错误则throw
      var _error4 = unhandledError;
      unhandledError = null;
      hasUnhandledError = false;
      throw _error4;
    }
  }

我们终于进入performWorkOnRoot，performWorkOnRoot的作用是区分同步渲染还是异步渲染，expirationTime等于1，因此进入同步。导步肯定为false

// https://github.com/RubyLouvre/anu 欢迎加star

function performWorkOnRoot(root, expirationTime) {

    isRendering = true;

    // Check if this is async work or sync/expired work.
    // TODO: Pass current time as argument to renderRoot, commitRoot
    if (expirationTime <= recalculateCurrentTime()) {
      // Flush sync work.
     
      var finishedWork = root.finishedWork;
      console.log("Flush sync work.", finishedWork)
      if (finishedWork !== null) {
        // This root is already complete. We can commit it.
        root.finishedWork = null;
        console.log("commitRoot")
        root.remainingExpirationTime = commitRoot(finishedWork);
      } else {
        root.finishedWork = null;
        console.log("renderRoot")
        finishedWork = renderRoot(root, expirationTime);
        if (finishedWork !== null) {
          console.log("继续commitRoot")
          // We&#39;ve completed the root. Commit it.
          root.remainingExpirationTime = commitRoot(finishedWork);
        }
      }
    } else {
      console.log("Flush async work.")
      // Flush async work.
      // ...略
    }

    isRendering = false;
  }

renderRoot也是怒长，React16代码的特点是许多巨型类，巨型方法，有JAVA之遗风。renderRoot只有前面几行是可能处理虚拟DOM（或叫fiber）,后面都是错误边界的

function renderRoot(root, expirationTime) {
   
    isWorking = true;

    // We're about to mutate the work-in-progress tree. If the root was pending
    // commit, it no longer is: we'll need to complete it again.
    root.isReadyForCommit = false;

    // Check if we're starting from a fresh stack, or if we're resuming from
    // previously yielded work.
    if (root !== nextRoot || expirationTime !== nextRenderExpirationTime || nextUnitOfWork === null) {
      // Reset the stack and start working from the root.
      resetContextStack();
      nextRoot = root;
      nextRenderExpirationTime = expirationTime;
      //可能是用来工作的代码
       console.log("createWorkInProgress")
      nextUnitOfWork = createWorkInProgress(nextRoot.current, null, expirationTime);
    }
    //可能是用来工作的代码
     console.log("startWorkLoopTimer")
    startWorkLoopTimer(nextUnitOfWork);
   // 处理错误边界
    var didError = false;
    var error = null;
    invokeGuardedCallback$1(null, workLoop, null, expirationTime);
    // An error was thrown during the render phase.
    while (didError) {
       console.log("componentDidCatch的相关实现")
      if (didFatal) {
        // This was a fatal error. Don't attempt to recover from it.
        firstUncaughtError = error;
        break;
      }

      var failedWork = nextUnitOfWork;
      if (failedWork === null) {
        // An error was thrown but there's no current unit of work. This can
        // happen during the commit phase if there's a bug in the renderer.
        didFatal = true;
        continue;
      }

      // 处理错误边界
      var boundary = captureError(failedWork, error);
      !(boundary !== null) ? invariant_1(false, 'Should have found an error boundary. This error is likely caused by a bug in React. Please file an issue.') : void 0;

      if (didFatal) {
        // The error we just captured was a fatal error. This happens
        // when the error propagates to the root more than once.
        continue;
      }
       // 处理错误边界
      didError = false;
      error = null;
      // We're finished working. Exit the error loop.
      break;
    }
   // 处理错误边界
    var uncaughtError = firstUncaughtError;

    // We're done performing work. Time to clean up.
    stopWorkLoopTimer(interruptedBy);
    interruptedBy = null;
    isWorking = false;
    didFatal = false;
    firstUncaughtError = null;
     // 处理错误边界
    if (uncaughtError !== null) {
      onUncaughtError(uncaughtError);
    }

    return root.isReadyForCommit ? root.current.alternate : null;
  }

  function resetContextStack() {
    // Reset the stack
    reset$1();
    // Reset the cursors
    resetContext();
    resetHostContainer();
  }

function reset$1() {
  console.log("reset",index)
  while (index > -1) {
    valueStack[index] = null;

    {
      fiberStack[index] = null;
    }

    index--;
  }
}

function resetContext() {
  consoel.log("resetContext")
  previousContext = emptyObject_1;
  contextStackCursor.current = emptyObject_1;
  didPerformWorkStackCursor.current = false;
}

  function resetHostContainer() {
    console.log("resetHostContainer",contextStackCursor, rootInstanceStackCursor, NO_CONTEXT )
    contextStackCursor.current = NO_CONTEXT;
    rootInstanceStackCursor.current = NO_CONTEXT;
  }

createWorkInProgress就是将根组件的fiber对象再复制一份，变成其alternate属性。因此 将虚拟DOM转换为真实DOM的重任就交给invokeGuardedCallback

var invokeGuardedCallback = function (name, func, context, a, b, c, d, e, f) {
  ReactErrorUtils._hasCaughtError = false;
  ReactErrorUtils._caughtError = null;
  var funcArgs = Array.prototype.slice.call(arguments, 3);
  try {
    func.apply(context, funcArgs);
  } catch (error) {
    ReactErrorUtils._caughtError = error;
    ReactErrorUtils._hasCaughtError = true;
  }
//这下面还有怒长（100－150L ）的关于错误边界的处理，略过
};

func为workLoop

//by 司徒正美， 加群：370262116 一起研究React与anujs

 function workLoop(expirationTime) {
    if (capturedErrors !== null) {
      // If there are unhandled errors, switch to the slow work loop.
      // TODO: How to avoid this check in the fast path? Maybe the renderer
      // could keep track of which roots have unhandled errors and call a
      // forked version of renderRoot.
      slowWorkLoopThatChecksForFailedWork(expirationTime);
      return;
    }
    if (nextRenderExpirationTime === NoWork || nextRenderExpirationTime > expirationTime) {
      return;
    }

    if (nextRenderExpirationTime <= mostRecentCurrentTime) {
      // Flush all expired work.
      while (nextUnitOfWork !== null) {
        console.log("performUnitOfWork",nextUnitOfWork)
        nextUnitOfWork = performUnitOfWork(nextUnitOfWork);
      }
    } else {
      // Flush asynchronous work until the deadline runs out of time.
      while (nextUnitOfWork !== null && !shouldYield()) {
        nextUnitOfWork = performUnitOfWork(nextUnitOfWork);
      }
    }
  }

我们终于看到工作的代码了。 这个nextUnitOfWork 是renderRoot生成的
performUnitOfWork与beginWork的代码，里面会根据fiber的tag进入各种操作

//by 司徒正美， 加群：370262116 一起研究React与anujs
// https://github.com/RubyLouvre/anu 欢迎加star

function performUnitOfWork(workInProgress) {
    // The current, flushed, state of this fiber is the alternate.
    // Ideally nothing should rely on this, but relying on it here
    // means that we don't need an additional field on the work in
    // progress.
    var current = workInProgress.alternate;

    // See if beginning this work spawns more work.
    startWorkTimer(workInProgress);
    {
      ReactDebugCurrentFiber.setCurrentFiber(workInProgress);
    }
    console.log("beginWork")
    var next = beginWork(current, workInProgress, nextRenderExpirationTime);
    {
      ReactDebugCurrentFiber.resetCurrentFiber();
    }
    if (true && ReactFiberInstrumentation_1.debugTool) {
      ReactFiberInstrumentation_1.debugTool.onBeginWork(workInProgress);
    }

    if (next === null) {
      console.log("next")
      // If this doesn't spawn new work, complete the current work.
      next = completeUnitOfWork(workInProgress);
    }

    ReactCurrentOwner.current = null;

    return next;
  }
function beginWork(current, workInProgress, renderExpirationTime) {
    if (workInProgress.expirationTime === NoWork || workInProgress.expirationTime > renderExpirationTime) {
      return bailoutOnLowPriority(current, workInProgress);
    }

    switch (workInProgress.tag) {
      case IndeterminateComponent:
        return mountIndeterminateComponent(current, workInProgress, renderExpirationTime);
      case FunctionalComponent:
        return updateFunctionalComponent(current, workInProgress);
      case ClassComponent:
        return updateClassComponent(current, workInProgress, renderExpirationTime);
      case HostRoot:
        return updateHostRoot(current, workInProgress, renderExpirationTime);
      case HostComponent:
        return updateHostComponent(current, workInProgress, renderExpirationTime);
      case HostText:
        return updateHostText(current, workInProgress);
      case CallHandlerPhase:
        // This is a restart. Reset the tag to the initial phase.
        workInProgress.tag = CallComponent;
      // Intentionally fall through since this is now the same.
      case CallComponent:
        return updateCallComponent(current, workInProgress, renderExpirationTime);
      case ReturnComponent:
        // A return component is just a placeholder, we can just run through the
        // next one immediately.
        return null;
      case HostPortal:
        return updatePortalComponent(current, workInProgress, renderExpirationTime);
      case Fragment:
        return updateFragment(current, workInProgress);
      default:
        invariant_1(false, 'Unknown unit of work tag. This error is likely caused by a bug in React. Please file an issue.');
    }
  }

我们再调查一下workInProgress.tag是什么

https://github.com/facebook/r...

这里有全部fiber节点的类型描述，我们创建一个对象

// https://github.com/RubyLouvre/anu 欢迎加star

var mapBeginWork = {
    3: "HostRoot 根组件",
    0: "IndeterminateComponent 只知道type为函数",
    2: "ClassComponent 普通类组件" ,
    5: "HostComponent 元素节点",
    6: "HostText 文本节点"
  }
  function beginWork(current, workInProgress, renderExpirationTime) {
    if (workInProgress.expirationTime === NoWork || workInProgress.expirationTime > renderExpirationTime) {
      return bailoutOnLowPriority(current, workInProgress);
    }
    console.log(workInProgress.tag, mapBeginWork[workInProgress.tag])
     switch (workInProgress.tag) {
     //略
     }
}

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nodejs中的fiber（纤程）库详解_node.js

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