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renderRoot的错误处理

1 ）概述

• 在 completeWork这个方法之后, 再次回到 renderRoot 里面
• 在 renderRoot 里面执行了 workLoop, 之后，对 workLoop 使用了try catch
• 如果在里面有任何一个节点在更新的过程当中 throw Error 都会被catch到
• catch到之后就是错误处理
  • 给报错节点增加 incomplete 副作用
    • incomplete 的副作用在 completeUnitOfWork 的时候，用来进行判断
    • 是要调用 completeWork，还是调用 unwindWork
  • 需要给父链上具有 error boundary 的节点增加副作用
    • 让它去收集错误以及进行一定的处理
  • 还需要创建错误相关的更新

2 ）源码

定位到 packages/react-reconciler/src/ReactFiberScheduler.js#L1293

在 renderRoot 里面的 do while 循环中

do {try {workLoop(isYieldy);// 在catch里面得到了一个 thrownValue, 这是一个error} catch (thrownValue) {resetContextDependences();resetHooks();// Reset in case completion throws.// This is only used in DEV and when replaying is on.let mayReplay;if (__DEV__ && replayFailedUnitOfWorkWithInvokeGuardedCallback) {mayReplay = mayReplayFailedUnitOfWork;mayReplayFailedUnitOfWork = true;}// 如果 nextUnitOfWork 等于 null，这是一个不属于正常流程里面的一个情况// 因为 nextUnitOfWork 是我们在更新一个节点之前，它是有值的更新// 更新节点之后，它会被赋成一个新的值// 一般来说它不应该是会存在 nextUnitOfWork 是 null 的一个情况// 即便 throw error 了，上一个 nextUnitOfWork 也没有主动去把它消除if (nextUnitOfWork === null) {// This is a fatal error.// 为 null 这种情况，被认为是一个致命的错误didFatal = true;// 调用 onUncaughtError，无法处理的错误被抛出了// 这个时候，react是会直接中断渲染染流程onUncaughtError(thrownValue);} else {// 非上述致命错误if (enableProfilerTimer && nextUnitOfWork.mode & ProfileMode) {// Record the time spent rendering before an error was thrown.// This avoids inaccurate Profiler durations in the case of a suspended render.stopProfilerTimerIfRunningAndRecordDelta(nextUnitOfWork, true);}if (__DEV__) {// Reset global debug state// We assume this is defined in DEV(resetCurrentlyProcessingQueue: any)();}if (__DEV__ && replayFailedUnitOfWorkWithInvokeGuardedCallback) {if (mayReplay) {const failedUnitOfWork: Fiber = nextUnitOfWork;replayUnitOfWork(failedUnitOfWork, thrownValue, isYieldy);}}// TODO: we already know this isn't true in some cases.// At least this shows a nicer error message until we figure out the cause.// https://github.com/facebook/react/issues/12449#issuecomment-386727431invariant(nextUnitOfWork !== null,'Failed to replay rendering after an error. This ' +'is likely caused by a bug in React. Please file an issue ' +'with a reproducing case to help us find it.',);const sourceFiber: Fiber = nextUnitOfWork;let returnFiber = sourceFiber.return;// 如果 returnFiber 等于 null, 说明这个错误是出现在更新 RootFiber 的过程当中// 那么 RootFiber 它是一个非常固定的节点，就是说它没有用户代码去进行一个参与的// 如果这个它出现了一个错误，也是一个致命的错误，是一个react源码级的一个错误，同上一样处理if (returnFiber === null) {// This is the root. The root could capture its own errors. However,// we don't know if it errors before or after we pushed the host// context. This information is needed to avoid a stack mismatch.// Because we're not sure, treat this as a fatal error. We could track// which phase it fails in, but doesn't seem worth it. At least// for now.didFatal = true;onUncaughtError(thrownValue);} else {// 这里是常规处理错误throwException(root,returnFiber,sourceFiber,thrownValue,nextRenderExpirationTime,);// 立刻完成当前节点，因为出错了，子树渲染没有意义了nextUnitOfWork = completeUnitOfWork(sourceFiber);continue;}}}break;} while (true);

• 进入 onUncaughtError

  function onUncaughtError(error: mixed) {invariant(nextFlushedRoot !== null,'Should be working on a root. This error is likely caused by a bug in ' +'React. Please file an issue.',);// Unschedule this root so we don't work on it again until there's// another update.// 这时候直接把 nextFlushedRoot 设置成 NoWork，剩下的任务都不再执行了nextFlushedRoot.expirationTime = NoWork;// 处理全局变量if (!hasUnhandledError) {hasUnhandledError = true;unhandledError = error;}
  }
  

• 进入 throwException 这个是常规处理错误的处理器

  function throwException(root: FiberRoot,returnFiber: Fiber,sourceFiber: Fiber,value: mixed,renderExpirationTime: ExpirationTime,
  ) {// 增加 Incomplete 这个 SideEffect// 这也是在 completeUnitOfWork 当中，去判断节点，是否有 Incomplete 的来源// 只有在这个节点，throw了一个异常之后，它才会被赋值 SideEffect// The source fiber did not complete.sourceFiber.effectTag |= Incomplete;// Its effect list is no longer valid.// 对 firstEffect 和 lastEffect 置 null// 因为它已经抛出一个异常了，子节点不会再进行渲染，不会有effect的一个链sourceFiber.firstEffect = sourceFiber.lastEffect = null;// 这种就匹配 Promise对象，或者 thenable 对象// 这个其实就对应 Suspense 相关的处理，通过 throw 一个 thenable 的对象// 可以让这个组件变成一个挂起的状态，等到这个 Promise 被 resolve之后，再次进入一个正常的渲染周期// 这部分都是跟 Suspense 相关的代码，先跳过if (value !== null &&typeof value === 'object' &&typeof value.then === 'function') {// This is a thenable.const thenable: Thenable = (value: any);// Find the earliest timeout threshold of all the placeholders in the// ancestor path. We could avoid this traversal by storing the thresholds on// the stack, but we choose not to because we only hit this path if we're// IO-bound (i.e. if something suspends). Whereas the stack is used even in// the non-IO- bound case.let workInProgress = returnFiber;let earliestTimeoutMs = -1;let startTimeMs = -1;do {if (workInProgress.tag === SuspenseComponent) {const current = workInProgress.alternate;if (current !== null) {const currentState: SuspenseState | null = current.memoizedState;if (currentState !== null && currentState.didTimeout) {// Reached a boundary that already timed out. Do not search// any further.const timedOutAt = currentState.timedOutAt;startTimeMs = expirationTimeToMs(timedOutAt);// Do not search any further.break;}}let timeoutPropMs = workInProgress.pendingProps.maxDuration;if (typeof timeoutPropMs === 'number') {if (timeoutPropMs <= 0) {earliestTimeoutMs = 0;} else if (earliestTimeoutMs === -1 ||timeoutPropMs < earliestTimeoutMs) {earliestTimeoutMs = timeoutPropMs;}}}workInProgress = workInProgress.return;} while (workInProgress !== null);// Schedule the nearest Suspense to re-render the timed out view.workInProgress = returnFiber;do {if (workInProgress.tag === SuspenseComponent &&shouldCaptureSuspense(workInProgress.alternate, workInProgress)) {// Found the nearest boundary.// If the boundary is not in concurrent mode, we should not suspend, and// likewise, when the promise resolves, we should ping synchronously.const pingTime =(workInProgress.mode & ConcurrentMode) === NoEffect? Sync: renderExpirationTime;// Attach a listener to the promise to "ping" the root and retry.let onResolveOrReject = retrySuspendedRoot.bind(null,root,workInProgress,sourceFiber,pingTime,);if (enableSchedulerTracing) {onResolveOrReject = Schedule_tracing_wrap(onResolveOrReject);}thenable.then(onResolveOrReject, onResolveOrReject);// If the boundary is outside of concurrent mode, we should *not*// suspend the commit. Pretend as if the suspended component rendered// null and keep rendering. In the commit phase, we'll schedule a// subsequent synchronous update to re-render the Suspense.//// Note: It doesn't matter whether the component that suspended was// inside a concurrent mode tree. If the Suspense is outside of it, we// should *not* suspend the commit.if ((workInProgress.mode & ConcurrentMode) === NoEffect) {workInProgress.effectTag |= CallbackEffect;// Unmount the source fiber's childrenconst nextChildren = null;reconcileChildren(sourceFiber.alternate,sourceFiber,nextChildren,renderExpirationTime,);sourceFiber.effectTag &= ~Incomplete;if (sourceFiber.tag === ClassComponent) {// We're going to commit this fiber even though it didn't complete.// But we shouldn't call any lifecycle methods or callbacks. Remove// all lifecycle effect tags.sourceFiber.effectTag &= ~LifecycleEffectMask;const current = sourceFiber.alternate;if (current === null) {// This is a new mount. Change the tag so it's not mistaken for a// completed component. For example, we should not call// componentWillUnmount if it is deleted.sourceFiber.tag = IncompleteClassComponent;}}// Exit without suspending.return;}// Confirmed that the boundary is in a concurrent mode tree. Continue// with the normal suspend path.let absoluteTimeoutMs;if (earliestTimeoutMs === -1) {// If no explicit threshold is given, default to an abitrarily large// value. The actual size doesn't matter because the threshold for the// whole tree will be clamped to the expiration time.absoluteTimeoutMs = maxSigned31BitInt;} else {if (startTimeMs === -1) {// This suspend happened outside of any already timed-out// placeholders. We don't know exactly when the update was// scheduled, but we can infer an approximate start time from the// expiration time. First, find the earliest uncommitted expiration// time in the tree, including work that is suspended. Then subtract// the offset used to compute an async update's expiration time.// This will cause high priority (interactive) work to expire// earlier than necessary, but we can account for this by adjusting// for the Just Noticeable Difference.const earliestExpirationTime = findEarliestOutstandingPriorityLevel(root,renderExpirationTime,);const earliestExpirationTimeMs = expirationTimeToMs(earliestExpirationTime,);startTimeMs = earliestExpirationTimeMs - LOW_PRIORITY_EXPIRATION;}absoluteTimeoutMs = startTimeMs + earliestTimeoutMs;}// Mark the earliest timeout in the suspended fiber's ancestor path.// After completing the root, we'll take the largest of all the// suspended fiber's timeouts and use it to compute a timeout for the// whole tree.renderDidSuspend(root, absoluteTimeoutMs, renderExpirationTime);workInProgress.effectTag |= ShouldCapture;workInProgress.expirationTime = renderExpirationTime;return;}// This boundary already captured during this render. Continue to the next// boundary.workInProgress = workInProgress.return;} while (workInProgress !== null);// No boundary was found. Fallthrough to error mode.value = new Error('An update was suspended, but no placeholder UI was provided.',);}// We didn't find a boundary that could handle this type of exception. Start// over and traverse parent path again, this time treating the exception// as an error.// renderDidError 方法 就是设置全局变量 nextRenderDidError 为 truerenderDidError();// 返回错误调用信息字符串value = createCapturedValue(value, sourceFiber);let workInProgress = returnFiber;// 根据tag匹配处理程序do {// 它其实就是往上去找它，要找到第一个可以处理错误的 class component // 来进行一个错误的update的一个创建，并且让它入栈// 等后期在commit的时候可以进行一个调用// 如果都没有，那么它会到 HostRoot 上面来进行处理错误// 因为 HostRoot 它相当于是一个内置的错误处理的方式// 也会创建对应的update，然后进行一个入队列，然后后续进行一个调用的过程// 这就是一个 throw exception，对于错误处理的一个情况switch (workInProgress.tag) {case HostRoot: {const errorInfo = value;workInProgress.effectTag |= ShouldCapture;workInProgress.expirationTime = renderExpirationTime;// 这个 update 类似于 setState 创建的对象const update = createRootErrorUpdate(workInProgress,errorInfo,renderExpirationTime,);enqueueCapturedUpdate(workInProgress, update);return;}// case ClassComponent:// Capture and retryconst errorInfo = value;const ctor = workInProgress.type;const instance = workInProgress.stateNode;// 它要先去判断一下，它现在没有 DidCapture 这个 SideEffect// 并且它是有 getDerivedStateFromError 这么一个方法// 或者它是有 componentDidCatch 生命周期方法if ((workInProgress.effectTag & DidCapture) === NoEffect &&(typeof ctor.getDerivedStateFromError === 'function' ||(instance !== null &&typeof instance.componentDidCatch === 'function' &&!isAlreadyFailedLegacyErrorBoundary(instance)))) {// 在这种情况下，我们就可以给它加上 ShouldCapture 这个 SideEffect// 并且呢设置它的 expirationTime 等于 renderExpirationTime// 因为我要去对这个组件, 在这个周期里面进行一个更新的过程// 然后他也要去创建一个update调用的是 createClassErrorUpdateworkInProgress.effectTag |= ShouldCapture;workInProgress.expirationTime = renderExpirationTime;// Schedule the error boundary to re-render using updated stateconst update = createClassErrorUpdate(workInProgress,errorInfo,renderExpirationTime,);enqueueCapturedUpdate(workInProgress, update);return;}break;default:break;}workInProgress = workInProgress.return;} while (workInProgress !== null);
  }
  

  • 进入 renderDidError

    // packages/react-reconciler/src/ReactFiberScheduler.js
    function renderDidError() {nextRenderDidError = true;
    }
    

  • 进入 createCapturedValue

    // packages/react-reconciler/src/ReactCapturedValue.js
    export function createCapturedValue<T>(value: T,source: Fiber,
    ): CapturedValue<T> {// If the value is an error, call this function immediately after it is thrown// so the stack is accurate.return {value,source,stack: getStackByFiberInDevAndProd(source),};
    }
    

    • 进入 getStackByFiberInDevAndProd

      function describeFiber(fiber: Fiber): string {switch (fiber.tag) {case IndeterminateComponent:case LazyComponent:case FunctionComponent:case ClassComponent:case HostComponent:case Mode:const owner = fiber._debugOwner;const source = fiber._debugSource;const name = getComponentName(fiber.type);let ownerName = null;if (owner) {ownerName = getComponentName(owner.type);}return describeComponentFrame(name, source, ownerName);default:return '';}
      }// 类似于js里面的error对象，它会有一个stack的信息
      // 就是哪个文件或者哪个方法调用的时候，它出现了错误，并且附上文件对应的代码的行数之类的信息
      export function getStackByFiberInDevAndProd(workInProgress: Fiber): string {let info = '';let node = workInProgress;// 形成一个错误调用信息的过程do {info += describeFiber(node);node = node.return;} while (node);return info;
      }
      

    • 进入 createRootErrorUpdate

      function createRootErrorUpdate(fiber: Fiber,errorInfo: CapturedValue<mixed>,expirationTime: ExpirationTime,
      ): Update<mixed> {const update = createUpdate(expirationTime);// Unmount the root by rendering null.update.tag = CaptureUpdate;// Caution: React DevTools currently depends on this property// being called "element".update.payload = {element: null};const error = errorInfo.value;update.callback = () => {// 打印 erroronUncaughtError(error);logError(fiber, errorInfo);};return update;
      }
      

    • 进入 enqueueCapturedUpdate

      // 没有则创建，有则克隆
      // 挂载 update
      export function enqueueCapturedUpdate<State>(workInProgress: Fiber,update: Update<State>,
      ) {// Captured updates go into a separate list, and only on the work-in-// progress queue.let workInProgressQueue = workInProgress.updateQueue;if (workInProgressQueue === null) {workInProgressQueue = workInProgress.updateQueue = createUpdateQueue(workInProgress.memoizedState,);} else {// TODO: I put this here rather than createWorkInProgress so that we don't// clone the queue unnecessarily. There's probably a better way to// structure this.workInProgressQueue = ensureWorkInProgressQueueIsAClone(workInProgress,workInProgressQueue,);}// Append the update to the end of the list.if (workInProgressQueue.lastCapturedUpdate === null) {// This is the first render phase updateworkInProgressQueue.firstCapturedUpdate = workInProgressQueue.lastCapturedUpdate = update;} else {workInProgressQueue.lastCapturedUpdate.next = update;workInProgressQueue.lastCapturedUpdate = update;}
      }
      

    • 进入 createClassErrorUpdate

      function createClassErrorUpdate(fiber: Fiber,errorInfo: CapturedValue<mixed>,expirationTime: ExpirationTime,
      ): Update<mixed> {// 创建 updateconst update = createUpdate(expirationTime);// 标记 tagupdate.tag = CaptureUpdate;const getDerivedStateFromError = fiber.type.getDerivedStateFromError;// 存在 getDerivedStateFromError 则作为 payload 回调处理if (typeof getDerivedStateFromError === 'function') {const error = errorInfo.value;update.payload = () => {return getDerivedStateFromError(error);};}const inst = fiber.stateNode;if (inst !== null && typeof inst.componentDidCatch === 'function') {// 这个有组件错误被捕获之后，它会向上去找有能够处理捕获错误信息的这个class component 来处理// 如果都没有，它才会到 root 上面来进行一个处理// 它会根据像 getDerivedStateFromError 以及 componentDidCatch 这些生命周期方法来进行一个处理// 如果都没有这个指定，那么这个classcomponent 是没有一个错误处理的功能的// 如果有就会对应的进行这些操作来进行一个调用update.callback = function callback() {if (typeof getDerivedStateFromError !== 'function') {// To preserve the preexisting retry behavior of error boundaries,// we keep track of which ones already failed during this batch.// This gets reset before we yield back to the browser.// TODO: Warn in strict mode if getDerivedStateFromError is// not defined.markLegacyErrorBoundaryAsFailed(this);}const error = errorInfo.value;const stack = errorInfo.stack;// 输出 errorlogError(fiber, errorInfo);// 调用catch回调钩子 传入 stackthis.componentDidCatch(error, {componentStack: stack !== null ? stack : '',});if (__DEV__) {if (typeof getDerivedStateFromError !== 'function') {// If componentDidCatch is the only error boundary method defined,// then it needs to call setState to recover from errors.// If no state update is scheduled then the boundary will swallow the error.warningWithoutStack(fiber.expirationTime === Sync,'%s: Error boundaries should implement getDerivedStateFromError(). ' +'In that method, return a state update to display an error message or fallback UI.',getComponentName(fiber.type) || 'Unknown',);}}};}return update;
      }
      

• 经过以上的处理，在调用了所有 exception 之后，最后 立马调用了 completeUnitOfWork

• 这就说明这个节点报错了，这个节点已经完成了，它不会再继续去渲染它的子节点了

• 因为这个节点它已经出错了，再渲染它的子节点是没有任何意义

• 所以在这里面，如果有一个节点，出错了，就会立马对它执行 completeUnitOfWork

• 它走的就是 unwindWork 的流程了, 这个后续来看