Viewing github.com/facebook/react/packages/scheduler/src/forks/SchedulerMock.js

```
/**
```

 * Copyright (c) Meta Platforms, Inc. and affiliates.

```
 *
```

 * This source code is licensed under the MIT license found in the

 * LICENSE file in the root directory of this source tree.

```
 *
```
```
 * @flow
```
```
 */
```
```
/* eslint-disable no-var */
```

/* eslint-disable react-internal/prod-error-codes */

import type {PriorityLevel} from '../SchedulerPriorities';

```
import {
```
```
  enableSchedulerDebugging,
```
```
  enableProfiling,
```
```
} from '../SchedulerFeatureFlags';
```

import {push, pop, peek} from '../SchedulerMinHeap';

```
// TODO: Use symbols?
```
```
import {
```
```
  ImmediatePriority,
```
```
  UserBlockingPriority,
```
```
  NormalPriority,
```
```
  LowPriority,
```
```
  IdlePriority,
```
```
} from '../SchedulerPriorities';
```
```
import {
```
```
  markTaskRun,
```
```
  markTaskYield,
```
```
  markTaskCompleted,
```
```
  markTaskCanceled,
```
```
  markTaskErrored,
```
```
  markSchedulerSuspended,
```
```
  markSchedulerUnsuspended,
```
```
  markTaskStart,
```
```
  stopLoggingProfilingEvents,
```
```
  startLoggingProfilingEvents,
```
```
} from '../SchedulerProfiling';
```
```
type Callback = boolean => ?Callback;
```
```
type Task = {
```
```
  id: number,
```
```
  callback: Callback | null,
```
```
  priorityLevel: PriorityLevel,
```
```
  startTime: number,
```
```
  expirationTime: number,
```
```
  sortIndex: number,
```
```
  isQueued?: boolean,
```
```
};
```

// Max 31 bit integer. The max integer size in V8 for 32-bit systems.

```
// Math.pow(2, 30) - 1
```
```
// 0b111111111111111111111111111111
```
```
var maxSigned31BitInt = 1073741823;
```
```
// Times out immediately
```
```
var IMMEDIATE_PRIORITY_TIMEOUT = -1;
```
```
// Eventually times out
```

var USER_BLOCKING_PRIORITY_TIMEOUT = 250;

```
var NORMAL_PRIORITY_TIMEOUT = 5000;
```
```
var LOW_PRIORITY_TIMEOUT = 10000;
```
```
// Never times out
```

var IDLE_PRIORITY_TIMEOUT = maxSigned31BitInt;

```
// Tasks are stored on a min heap
```
```
var taskQueue: Array<Task> = [];
```
```
var timerQueue: Array<Task> = [];
```

// Incrementing id counter. Used to maintain insertion order.

```
var taskIdCounter = 1;
```

// Pausing the scheduler is useful for debugging.

```
var isSchedulerPaused = false;
```
```
var currentTask = null;
```

var currentPriorityLevel = NormalPriority;

// This is set while performing work, to prevent re-entrance.

```
var isPerformingWork = false;
```
```
var isHostCallbackScheduled = false;
```
```
var isHostTimeoutScheduled = false;
```
```
let currentMockTime: number = 0;
```
```
let scheduledCallback:
```
```
  | null
```
```
  | ((
```
```
      hasTimeRemaining: boolean,
```

      initialTime: DOMHighResTimeStamp | number,

```
    ) => boolean) = null;
```

let scheduledTimeout: (number => void) | null = null;

```
let timeoutTime: number = -1;
```

let yieldedValues: Array<mixed> | null = null;

let expectedNumberOfYields: number = -1;

```
let didStop: boolean = false;
```
```
let isFlushing: boolean = false;
```
```
let needsPaint: boolean = false;
```

let shouldYieldForPaint: boolean = false;

```
var disableYieldValue = false;
```

function setDisableYieldValue(newValue: boolean) {

```
  disableYieldValue = newValue;
```
```
}
```

function advanceTimers(currentTime: number) {

  // Check for tasks that are no longer delayed and add them to the queue.

```
  let timer = peek(timerQueue);
```
```
  while (timer !== null) {
```
```
    if (timer.callback === null) {
```
```
      // Timer was cancelled.
```
```
      pop(timerQueue);
```

    } else if (timer.startTime <= currentTime) {

      // Timer fired. Transfer to the task queue.

```
      pop(timerQueue);
```

      timer.sortIndex = timer.expirationTime;

```
      push(taskQueue, timer);
```
```
      if (enableProfiling) {
```

        markTaskStart(timer, currentTime);

```
        timer.isQueued = true;
```
```
      }
```
```
    } else {
```
```
      // Remaining timers are pending.
```
```
      return;
```
```
    }
```
```
    timer = peek(timerQueue);
```
```
  }
```
```
}
```

function handleTimeout(currentTime: number) {

```
  isHostTimeoutScheduled = false;
```
```
  advanceTimers(currentTime);
```
```
  if (!isHostCallbackScheduled) {
```
```
    if (peek(taskQueue) !== null) {
```
```
      isHostCallbackScheduled = true;
```
```
      requestHostCallback(flushWork);
```
```
    } else {
```

      const firstTimer = peek(timerQueue);

```
      if (firstTimer !== null) {
```

        requestHostTimeout(handleTimeout, firstTimer.startTime - currentTime);

```
      }
```
```
    }
```
```
  }
```
```
}
```

function flushWork(hasTimeRemaining: boolean, initialTime: number) {

```
  if (enableProfiling) {
```

    markSchedulerUnsuspended(initialTime);

```
  }
```

  // We'll need a host callback the next time work is scheduled.

```
  isHostCallbackScheduled = false;
```
```
  if (isHostTimeoutScheduled) {
```

    // We scheduled a timeout but it's no longer needed. Cancel it.

```
    isHostTimeoutScheduled = false;
```
```
    cancelHostTimeout();
```
```
  }
```
```
  isPerformingWork = true;
```

  const previousPriorityLevel = currentPriorityLevel;

```
  try {
```
```
    if (enableProfiling) {
```
```
      try {
```

        return workLoop(hasTimeRemaining, initialTime);

```
      } catch (error) {
```
```
        if (currentTask !== null) {
```

          const currentTime = getCurrentTime();

          // $FlowFixMe[incompatible-call] found when upgrading Flow

          markTaskErrored(currentTask, currentTime);

          // $FlowFixMe[incompatible-use] found when upgrading Flow

          currentTask.isQueued = false;

```
        }
```
```
        throw error;
```
```
      }
```
```
    } else {
```
```
      // No catch in prod code path.
```

      return workLoop(hasTimeRemaining, initialTime);

```
    }
```
```
  } finally {
```
```
    currentTask = null;
```

    currentPriorityLevel = previousPriorityLevel;

```
    isPerformingWork = false;
```
```
    if (enableProfiling) {
```

      const currentTime = getCurrentTime();

      markSchedulerSuspended(currentTime);

```
    }
```
```
  }
```
```
}
```

function workLoop(hasTimeRemaining: boolean, initialTime: number): boolean {

```
  let currentTime = initialTime;
```
```
  advanceTimers(currentTime);
```
```
  currentTask = peek(taskQueue);
```
```
  while (
```
```
    currentTask !== null &&
```

    !(enableSchedulerDebugging && isSchedulerPaused)

```
  ) {
```
```
    if (
```

      currentTask.expirationTime > currentTime &&

      (!hasTimeRemaining || shouldYieldToHost())

```
    ) {
```

      // This currentTask hasn't expired, and we've reached the deadline.

```
      break;
```
```
    }
```

    // $FlowFixMe[incompatible-use] found when upgrading Flow

    const callback = currentTask.callback;

    if (typeof callback === 'function') {

      // $FlowFixMe[incompatible-use] found when upgrading Flow

```
      currentTask.callback = null;
```

      // $FlowFixMe[incompatible-use] found when upgrading Flow

      currentPriorityLevel = currentTask.priorityLevel;

      // $FlowFixMe[incompatible-use] found when upgrading Flow

      const didUserCallbackTimeout = currentTask.expirationTime <= currentTime;

```
      if (enableProfiling) {
```

        // $FlowFixMe[incompatible-call] found when upgrading Flow

        markTaskRun(currentTask, currentTime);

```
      }
```

      const continuationCallback = callback(didUserCallbackTimeout);

```
      currentTime = getCurrentTime();
```

      if (typeof continuationCallback === 'function') {

        // If a continuation is returned, immediately yield to the main thread

        // regardless of how much time is left in the current time slice.

        // $FlowFixMe[incompatible-use] found when upgrading Flow

        currentTask.callback = continuationCallback;

```
        if (enableProfiling) {
```

          // $FlowFixMe[incompatible-call] found when upgrading Flow

          markTaskYield(currentTask, currentTime);

```
        }
```
```
        advanceTimers(currentTime);
```
```
        if (shouldYieldForPaint) {
```
```
          needsPaint = true;
```
```
          return true;
```
```
        } else {
```

          // If `shouldYieldForPaint` is false, we keep flushing synchronously

          // without yielding to the main thread. This is the behavior of the

          // `toFlushAndYield` and `toFlushAndYieldThrough` testing helpers .

```
        }
```
```
      } else {
```
```
        if (enableProfiling) {
```

          // $FlowFixMe[incompatible-call] found when upgrading Flow

          markTaskCompleted(currentTask, currentTime);

          // $FlowFixMe[incompatible-use] found when upgrading Flow

          currentTask.isQueued = false;

```
        }
```

        if (currentTask === peek(taskQueue)) {

```
          pop(taskQueue);
```
```
        }
```
```
        advanceTimers(currentTime);
```
```
      }
```
```
    } else {
```
```
      pop(taskQueue);
```
```
    }
```
```
    currentTask = peek(taskQueue);
```
```
  }
```

  // Return whether there's additional work

```
  if (currentTask !== null) {
```
```
    return true;
```
```
  } else {
```

    const firstTimer = peek(timerQueue);

```
    if (firstTimer !== null) {
```

      requestHostTimeout(handleTimeout, firstTimer.startTime - currentTime);

```
    }
```
```
    return false;
```
```
  }
```
```
}
```
```
function unstable_runWithPriority<T>(
```
```
  priorityLevel: PriorityLevel,
```
```
  eventHandler: () => T,
```
```
): T {
```
```
  switch (priorityLevel) {
```
```
    case ImmediatePriority:
```
```
    case UserBlockingPriority:
```
```
    case NormalPriority:
```
```
    case LowPriority:
```
```
    case IdlePriority:
```
```
      break;
```
```
    default:
```
```
      priorityLevel = NormalPriority;
```
```
  }
```

  var previousPriorityLevel = currentPriorityLevel;

  currentPriorityLevel = priorityLevel;

```
  try {
```
```
    return eventHandler();
```
```
  } finally {
```

    currentPriorityLevel = previousPriorityLevel;

```
  }
```
```
}
```

function unstable_next<T>(eventHandler: () => T): T {

```
  var priorityLevel;
```
```
  switch (currentPriorityLevel) {
```
```
    case ImmediatePriority:
```
```
    case UserBlockingPriority:
```
```
    case NormalPriority:
```
```
      // Shift down to normal priority
```
```
      priorityLevel = NormalPriority;
```
```
      break;
```
```
    default:
```

      // Anything lower than normal priority should remain at the current level.

      priorityLevel = currentPriorityLevel;

```
      break;
```
```
  }
```

  var previousPriorityLevel = currentPriorityLevel;

  currentPriorityLevel = priorityLevel;

```
  try {
```
```
    return eventHandler();
```
```
  } finally {
```

    currentPriorityLevel = previousPriorityLevel;

```
  }
```
```
}
```

function unstable_wrapCallback<T: (...Array<mixed>) => mixed>(callback: T): T {

  var parentPriorityLevel = currentPriorityLevel;

```
  // $FlowFixMe[incompatible-return]
```
```
  // $FlowFixMe[missing-this-annot]
```
```
  return function () {
```

    // This is a fork of runWithPriority, inlined for performance.

    var previousPriorityLevel = currentPriorityLevel;

    currentPriorityLevel = parentPriorityLevel;

```
    try {
```

      return callback.apply(this, arguments);

```
    } finally {
```

      currentPriorityLevel = previousPriorityLevel;

```
    }
```
```
  };
```
```
}
```
```
function unstable_scheduleCallback(
```
```
  priorityLevel: PriorityLevel,
```
```
  callback: Callback,
```
```
  options?: {delay: number},
```
```
): Task {
```
```
  var currentTime = getCurrentTime();
```
```
  var startTime;
```

  if (typeof options === 'object' && options !== null) {

```
    var delay = options.delay;
```

    if (typeof delay === 'number' && delay > 0) {

```
      startTime = currentTime + delay;
```
```
    } else {
```
```
      startTime = currentTime;
```
```
    }
```
```
  } else {
```
```
    startTime = currentTime;
```
```
  }
```
```
  var timeout;
```
```
  switch (priorityLevel) {
```
```
    case ImmediatePriority:
```

      timeout = IMMEDIATE_PRIORITY_TIMEOUT;

```
      break;
```
```
    case UserBlockingPriority:
```

      timeout = USER_BLOCKING_PRIORITY_TIMEOUT;

```
      break;
```
```
    case IdlePriority:
```
```
      timeout = IDLE_PRIORITY_TIMEOUT;
```
```
      break;
```
```
    case LowPriority:
```
```
      timeout = LOW_PRIORITY_TIMEOUT;
```
```
      break;
```
```
    case NormalPriority:
```
```
    default:
```

      timeout = NORMAL_PRIORITY_TIMEOUT;

```
      break;
```
```
  }
```

  var expirationTime = startTime + timeout;

```
  var newTask: Task = {
```
```
    id: taskIdCounter++,
```
```
    callback,
```
```
    priorityLevel,
```
```
    startTime,
```
```
    expirationTime,
```
```
    sortIndex: -1,
```
```
  };
```
```
  if (enableProfiling) {
```
```
    newTask.isQueued = false;
```
```
  }
```
```
  if (startTime > currentTime) {
```
```
    // This is a delayed task.
```
```
    newTask.sortIndex = startTime;
```
```
    push(timerQueue, newTask);
```

    if (peek(taskQueue) === null && newTask === peek(timerQueue)) {

      // All tasks are delayed, and this is the task with the earliest delay.

```
      if (isHostTimeoutScheduled) {
```
```
        // Cancel an existing timeout.
```
```
        cancelHostTimeout();
```
```
      } else {
```
```
        isHostTimeoutScheduled = true;
```
```
      }
```
```
      // Schedule a timeout.
```

      requestHostTimeout(handleTimeout, startTime - currentTime);

```
    }
```
```
  } else {
```

    newTask.sortIndex = expirationTime;

```
    push(taskQueue, newTask);
```
```
    if (enableProfiling) {
```

      markTaskStart(newTask, currentTime);

```
      newTask.isQueued = true;
```
```
    }
```

    // Schedule a host callback, if needed. If we're already performing work,

    // wait until the next time we yield.

    if (!isHostCallbackScheduled && !isPerformingWork) {

```
      isHostCallbackScheduled = true;
```
```
      requestHostCallback(flushWork);
```
```
    }
```
```
  }
```
```
  return newTask;
```
```
}
```
```
function unstable_pauseExecution() {
```
```
  isSchedulerPaused = true;
```
```
}
```

function unstable_continueExecution() {

```
  isSchedulerPaused = false;
```

  if (!isHostCallbackScheduled && !isPerformingWork) {

```
    isHostCallbackScheduled = true;
```
```
    requestHostCallback(flushWork);
```
```
  }
```
```
}
```

function unstable_getFirstCallbackNode(): Task | null {

```
  return peek(taskQueue);
```
```
}
```

function unstable_cancelCallback(task: Task) {

```
  if (enableProfiling) {
```
```
    if (task.isQueued) {
```

      const currentTime = getCurrentTime();

      markTaskCanceled(task, currentTime);

```
      task.isQueued = false;
```
```
    }
```
```
  }
```

  // Null out the callback to indicate the task has been canceled. (Can't

  // remove from the queue because you can't remove arbitrary nodes from an

  // array based heap, only the first one.)

```
  task.callback = null;
```
```
}
```

function unstable_getCurrentPriorityLevel(): PriorityLevel {

```
  return currentPriorityLevel;
```
```
}
```

function requestHostCallback(callback: (boolean, number) => boolean) {

```
  scheduledCallback = callback;
```
```
}
```

function requestHostTimeout(callback: number => void, ms: number) {

```
  scheduledTimeout = callback;
```
```
  timeoutTime = currentMockTime + ms;
```
```
}
```
```
function cancelHostTimeout(): void {
```
```
  scheduledTimeout = null;
```
```
  timeoutTime = -1;
```
```
}
```

function shouldYieldToHost(): boolean {

```
  if (
```

    (expectedNumberOfYields === 0 && yieldedValues === null) ||

```
    (expectedNumberOfYields !== -1 &&
```
```
      yieldedValues !== null &&
```

      yieldedValues.length >= expectedNumberOfYields) ||

    (shouldYieldForPaint && needsPaint)

```
  ) {
```

    // We yielded at least as many values as expected. Stop flushing.

```
    didStop = true;
```
```
    return true;
```
```
  }
```
```
  return false;
```
```
}
```
```
function getCurrentTime(): number {
```
```
  return currentMockTime;
```
```
}
```
```
function forceFrameRate() {
```
```
  // No-op
```
```
}
```
```
function reset() {
```
```
  if (isFlushing) {
```

    throw new Error('Cannot reset while already flushing work.');

```
  }
```
```
  currentMockTime = 0;
```
```
  scheduledCallback = null;
```
```
  scheduledTimeout = null;
```
```
  timeoutTime = -1;
```
```
  yieldedValues = null;
```
```
  expectedNumberOfYields = -1;
```
```
  didStop = false;
```
```
  isFlushing = false;
```
```
  needsPaint = false;
```
```
}
```

// Should only be used via an assertion helper that inspects the yielded values.

function unstable_flushNumberOfYields(count: number): void {

```
  if (isFlushing) {
```

    throw new Error('Already flushing work.');

```
  }
```
```
  if (scheduledCallback !== null) {
```
```
    const cb = scheduledCallback;
```
```
    expectedNumberOfYields = count;
```
```
    isFlushing = true;
```
```
    try {
```
```
      let hasMoreWork = true;
```
```
      do {
```

        hasMoreWork = cb(true, currentMockTime);

      } while (hasMoreWork && !didStop);

```
      if (!hasMoreWork) {
```
```
        scheduledCallback = null;
```
```
      }
```
```
    } finally {
```
```
      expectedNumberOfYields = -1;
```
```
      didStop = false;
```
```
      isFlushing = false;
```
```
    }
```
```
  }
```
```
}
```

function unstable_flushUntilNextPaint(): false {

```
  if (isFlushing) {
```

    throw new Error('Already flushing work.');

```
  }
```
```
  if (scheduledCallback !== null) {
```
```
    const cb = scheduledCallback;
```
```
    shouldYieldForPaint = true;
```
```
    needsPaint = false;
```
```
    isFlushing = true;
```
```
    try {
```
```
      let hasMoreWork = true;
```
```
      do {
```

        hasMoreWork = cb(true, currentMockTime);

      } while (hasMoreWork && !didStop);

```
      if (!hasMoreWork) {
```
```
        scheduledCallback = null;
```
```
      }
```
```
    } finally {
```
```
      shouldYieldForPaint = false;
```
```
      didStop = false;
```
```
      isFlushing = false;
```
```
    }
```
```
  }
```
```
  return false;
```
```
}
```

function unstable_hasPendingWork(): boolean {

```
  return scheduledCallback !== null;
```
```
}
```
```
function unstable_flushExpired() {
```
```
  if (isFlushing) {
```

    throw new Error('Already flushing work.');

```
  }
```
```
  if (scheduledCallback !== null) {
```
```
    isFlushing = true;
```
```
    try {
```

      const hasMoreWork = scheduledCallback(false, currentMockTime);

```
      if (!hasMoreWork) {
```
```
        scheduledCallback = null;
```
```
      }
```
```
    } finally {
```
```
      isFlushing = false;
```
```
    }
```
```
  }
```
```
}
```

function unstable_flushAllWithoutAsserting(): boolean {

  // Returns false if no work was flushed.

```
  if (isFlushing) {
```

    throw new Error('Already flushing work.');

```
  }
```
```
  if (scheduledCallback !== null) {
```
```
    const cb = scheduledCallback;
```
```
    isFlushing = true;
```
```
    try {
```
```
      let hasMoreWork = true;
```
```
      do {
```

        hasMoreWork = cb(true, currentMockTime);

```
      } while (hasMoreWork);
```
```
      if (!hasMoreWork) {
```
```
        scheduledCallback = null;
```
```
      }
```
```
      return true;
```
```
    } finally {
```
```
      isFlushing = false;
```
```
    }
```
```
  } else {
```
```
    return false;
```
```
  }
```
```
}
```

function unstable_clearLog(): Array<mixed> {

```
  if (yieldedValues === null) {
```
```
    return [];
```
```
  }
```
```
  const values = yieldedValues;
```
```
  yieldedValues = null;
```
```
  return values;
```
```
}
```
```
function unstable_flushAll(): void {
```
```
  if (yieldedValues !== null) {
```
```
    throw new Error(
```

      'Log is not empty. Assert on the log of yielded values before ' +

```
        'flushing additional work.',
```
```
    );
```
```
  }
```
```
  unstable_flushAllWithoutAsserting();
```
```
  if (yieldedValues !== null) {
```
```
    throw new Error(
```

      'While flushing work, something yielded a value. Use an ' +

        'assertion helper to assert on the log of yielded values, e.g. ' +

        'expect(Scheduler).toFlushAndYield([...])',

```
    );
```
```
  }
```
```
}
```
```
function log(value: mixed): void {
```

  // eslint-disable-next-line react-internal/no-production-logging

  if (console.log.name === 'disabledLog' || disableYieldValue) {

    // If console.log has been patched, we assume we're in render

    // replaying and we ignore any values yielding in the second pass.

```
    return;
```
```
  }
```
```
  if (yieldedValues === null) {
```
```
    yieldedValues = [value];
```
```
  } else {
```
```
    yieldedValues.push(value);
```
```
  }
```
```
}
```

function unstable_advanceTime(ms: number) {

  // eslint-disable-next-line react-internal/no-production-logging

  if (console.log.name === 'disabledLog' || disableYieldValue) {

    // If console.log has been patched, we assume we're in render

    // replaying and we ignore any time advancing in the second pass.

```
    return;
```
```
  }
```
```
  currentMockTime += ms;
```

  if (scheduledTimeout !== null && timeoutTime <= currentMockTime) {

```
    scheduledTimeout(currentMockTime);
```
```
    timeoutTime = -1;
```
```
    scheduledTimeout = null;
```
```
  }
```
```
}
```
```
function requestPaint() {
```
```
  needsPaint = true;
```
```
}
```
```
export {
```

  ImmediatePriority as unstable_ImmediatePriority,

  UserBlockingPriority as unstable_UserBlockingPriority,

  NormalPriority as unstable_NormalPriority,

  IdlePriority as unstable_IdlePriority,

```
  LowPriority as unstable_LowPriority,
```
```
  unstable_runWithPriority,
```
```
  unstable_next,
```
```
  unstable_scheduleCallback,
```
```
  unstable_cancelCallback,
```
```
  unstable_wrapCallback,
```
```
  unstable_getCurrentPriorityLevel,
```

  shouldYieldToHost as unstable_shouldYield,

  requestPaint as unstable_requestPaint,

```
  unstable_continueExecution,
```
```
  unstable_pauseExecution,
```
```
  unstable_getFirstCallbackNode,
```
```
  getCurrentTime as unstable_now,
```

  forceFrameRate as unstable_forceFrameRate,

```
  unstable_flushAllWithoutAsserting,
```
```
  unstable_flushNumberOfYields,
```
```
  unstable_flushExpired,
```
```
  unstable_clearLog,
```
```
  unstable_flushUntilNextPaint,
```
```
  unstable_hasPendingWork,
```
```
  unstable_flushAll,
```
```
  log,
```
```
  unstable_advanceTime,
```
```
  reset,
```

  setDisableYieldValue as unstable_setDisableYieldValue,

```
};
```
```
export const unstable_Profiling: {
```
```
  startLoggingProfilingEvents(): void,
```

  stopLoggingProfilingEvents(): ArrayBuffer | null,

```
} | null = enableProfiling
```
```
  ? {
```
```
      startLoggingProfilingEvents,
```
```
      stopLoggingProfilingEvents,
```
```
    }
```
```
  : null;
```