Source: Scheduler.js 
/**
* 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.
*
*/
/* eslint-disable no-var */
import {
enableSchedulerDebugging,
enableProfiling,
} from './SchedulerFeatureFlags';
import {
requestHostCallback,
requestHostTimeout,
cancelHostTimeout,
shouldYieldToHost,
getCurrentTime,
forceFrameRate,
requestPaint,
} from './SchedulerHostConfig';
import {push, pop, peek} from './SchedulerMinHeap';
// TODO: Use symbols?
import {
ImmediatePriority,
UserBlockingPriority,
NormalPriority,
LowPriority,
IdlePriority,
} from './SchedulerPriorities';
import {
sharedProfilingBuffer,
markTaskRun,
markTaskYield,
markTaskCompleted,
markTaskCanceled,
markTaskErrored,
markSchedulerSuspended,
markSchedulerUnsuspended,
markTaskStart,
stopLoggingProfilingEvents,
startLoggingProfilingEvents,
} from './SchedulerProfiling';
// 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 = 250;
var NORMAL_PRIORITY_TIMEOUT = 5000;
var LOW_PRIORITY_TIMEOUT = 10000;
// Never times out
var IDLE_PRIORITY = maxSigned31BitInt;
// Tasks are stored on a min heap
var taskQueue = [];
var timerQueue = [];
// 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-entrancy.
var isPerformingWork = false;
var isHostCallbackScheduled = false;
var isHostTimeoutScheduled = false;
function advanceTimers(currentTime) {
// 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) {
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, initialTime) {
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();
markTaskErrored(currentTask, currentTime);
currentTask.isQueued = false;
}
throw error;
}
} else {
// No catch in prod codepath.
return workLoop(hasTimeRemaining, initialTime);
}
} finally {
currentTask = null;
currentPriorityLevel = previousPriorityLevel;
isPerformingWork = false;
if (enableProfiling) {
const currentTime = getCurrentTime();
markSchedulerSuspended(currentTime);
}
}
}
function workLoop(hasTimeRemaining, initialTime) {
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;
}
const callback = currentTask.callback;
if (callback !== null) {
currentTask.callback = null;
currentPriorityLevel = currentTask.priorityLevel;
const didUserCallbackTimeout = currentTask.expirationTime <= currentTime;
markTaskRun(currentTask, currentTime);
const continuationCallback = callback(didUserCallbackTimeout);
currentTime = getCurrentTime();
if (typeof continuationCallback === 'function') {
currentTask.callback = continuationCallback;
markTaskYield(currentTask, currentTime);
} else {
if (enableProfiling) {
markTaskCompleted(currentTask, currentTime);
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 {
let firstTimer = peek(timerQueue);
if (firstTimer !== null) {
requestHostTimeout(handleTimeout, firstTimer.startTime - currentTime);
}
return false;
}
}
function unstable_runWithPriority(priorityLevel, eventHandler) {
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(eventHandler) {
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(callback) {
var parentPriorityLevel = currentPriorityLevel;
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 timeoutForPriorityLevel(priorityLevel) {
switch (priorityLevel) {
case ImmediatePriority:
return IMMEDIATE_PRIORITY_TIMEOUT;
case UserBlockingPriority:
return USER_BLOCKING_PRIORITY;
case IdlePriority:
return IDLE_PRIORITY;
case LowPriority:
return LOW_PRIORITY_TIMEOUT;
case NormalPriority:
default:
return NORMAL_PRIORITY_TIMEOUT;
}
}
function unstable_scheduleCallback(priorityLevel, callback, options) {
var currentTime = getCurrentTime();
var startTime;
var timeout;
if (typeof options === 'object' && options !== null) {
var delay = options.delay;
if (typeof delay === 'number' && delay > 0) {
startTime = currentTime + delay;
} else {
startTime = currentTime;
}
timeout =
typeof options.timeout === 'number'
? options.timeout
: timeoutForPriorityLevel(priorityLevel);
} else {
timeout = timeoutForPriorityLevel(priorityLevel);
startTime = currentTime;
}
var expirationTime = startTime + timeout;
var newTask = {
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() {
return peek(taskQueue);
}
function unstable_cancelCallback(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() {
return currentPriorityLevel;
}
function unstable_shouldYield() {
const currentTime = getCurrentTime();
advanceTimers(currentTime);
const firstTask = peek(taskQueue);
return (
(firstTask !== currentTask &&
currentTask !== null &&
firstTask !== null &&
firstTask.callback !== null &&
firstTask.startTime <= currentTime &&
firstTask.expirationTime < currentTask.expirationTime) ||
shouldYieldToHost()
);
}
const unstable_requestPaint = requestPaint;
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,
unstable_shouldYield,
unstable_requestPaint,
unstable_continueExecution,
unstable_pauseExecution,
unstable_getFirstCallbackNode,
getCurrentTime as unstable_now,
forceFrameRate as unstable_forceFrameRate,
};
export const unstable_Profiling = enableProfiling
? {
startLoggingProfilingEvents,
stopLoggingProfilingEvents,
sharedProfilingBuffer,
}
: null;
