react\packages\scheduler\src\SchedulerMinHeap.js
export function push(heap, node) {
const index = heap.length;
heap.push(node);
siftUp(heap, node, index);
}
export function peek(heap) {
const first = heap[0];
return first === undefined ? null : first;
}
export function pop(heap) {
const first = heap[0];
if (first !== undefined) {
const last = heap.pop();
if (last !== first) {
heap[0] = last;
siftDown(heap, last, 0);
}
return first;
} else {
return null;
}
}
function siftUp(heap, node, i) {
let index = i;
while (true) {
const parentIndex = index - 1 >>> 1;
const parent = heap[parentIndex];
if (parent !== undefined && compare(parent, node) > 0) {
heap[parentIndex] = node;
heap[index] = parent;
index = parentIndex;
} else {
return;
}
}
}
function siftDown(heap, node, i) {
let index = i;
const length = heap.length;
while (index < length) {
const leftIndex = (index + 1) * 2 - 1;
const left = heap[leftIndex];
const rightIndex = leftIndex + 1;
const right = heap[rightIndex];
if (left !== undefined && compare(left, node) < 0) {
if (right !== undefined && compare(right, left) < 0) {
heap[index] = right;
heap[rightIndex] = node;
index = rightIndex;
} else {
heap[index] = left;
heap[leftIndex] = node;
index = leftIndex;
}
} else if (right !== undefined && compare(right, node) < 0) {
heap[index] = right;
heap[rightIndex] = node;
index = rightIndex;
} else {
return;
}
}
}
function compare(a, b) {
const diff = a.sortIndex - b.sortIndex;
return diff !== 0 ? diff : a.id - b.id;
}
requestIdleCallback
目前只有Chrome支持var channel = new MessageChannel();
//channel.port1
//channel.port2
var channel = new MessageChannel();
var port1 = channel.port1;
var port2 = channel.port2;
port1.onmessage = function(event) {
console.log("port1收到来自port2的数据:" + event.data);
}
port2.onmessage = function(event) {
console.log("port2收到来自port1的数据:" + event.data);
}
port1.postMessage("发送给port2");
port2.postMessage("发送给port1");
src\index.js
import { scheduleCallback } from "./scheduler";
function calculate() {
let result = 0;
for (let i = 0; i < 100000000; i++) {
//8个0
result += 1;
}
console.log(result);
}
scheduleCallback(calculate);
src\scheduler\index.js
export * from './src/Scheduler';
src\scheduler\src\Scheduler.js
/**
* 调度一个工作
* @param {*} callback 要执行的工作
*/
function scheduleCallback(callback) {
//执行工作
callback();
}
export {
scheduleCallback
}
+import { scheduleCallback, shouldYield } from "./scheduler";
let result = 0;
let i = 0;
/**
* 总任务
* @returns
*/
function calculate() {
+ for (; i < 10000000 && (!shouldYield()); i++) {//7个0
+ result += 1;
+ }
+ if (result < 10000000) {
+ return calculate;
+ } else {
+ console.log('result', result);
+ return null;
+ }
}
scheduleCallback(calculate);
src\scheduler\src\Scheduler.js
+import { requestHostCallback, shouldYieldToHost } from './SchedulerHostConfig';
/**
* 调度一个工作
* @param {*} callback 要执行的工作
*/
function scheduleCallback(callback) {
//执行工作
+ requestHostCallback(callback);
}
export {
scheduleCallback,
+ shouldYieldToHost as shouldYield
}
src\scheduler\src\SchedulerHostConfig.js
//截止时间
let deadline = 0;
//当前正在调度执行的工作
let scheduledHostCallback = null;
//每帧的时间片
let yieldInterval = 5;
const channel = new MessageChannel();
channel.port1.onmessage = performWorkUntilDeadline;
/**
* 获取当前的时间戳
* @returns 当前的时间戳
*/
export function getCurrentTime() {
return performance.now();
}
/**
* 判断是否到达了本帧的截止时间
* @returns 是否需要暂停执行
*/
export function shouldYieldToHost() {
const currentTime = getCurrentTime();
return currentTime >= deadline;
};
/**
* 执行工作直到截止时间
*/
export function performWorkUntilDeadline() {
const currentTime = getCurrentTime();
//计算截止时间
deadline = currentTime + yieldInterval;
//执行工作
const hasMoreWork = scheduledHostCallback();
//如果此工作还没有执行完,则再次调度
if (hasMoreWork) {
channel.port2.postMessage(null);
}
}
/**
* 请求宿主的回调函数执行
* @param {*} callback
*/
export function requestHostCallback(callback) {
scheduledHostCallback = callback;
channel.port2.postMessage(null);
};
src\index.js
import { scheduleCallback, shouldYield } from "./scheduler";
let result = 0;
let i = 0;
/**
* 总任务
* @returns
*/
function calculate() {
for (; i < 10000000 && (!shouldYield()); i++) {//7个0
result += 1;
}
if (result < 10000000) {
return calculate;
} else {
console.log('result', result);
return null;
}
}
+let result2 = 0;
+let i2 = 0;
+/**
+ * 总任务
+ * @returns
+ */
+function calculate2() {
+ for (; i2 < 10000000 && (!shouldYield()); i2++) {
+ result2 += 1;
+ }
+ if (result2 < 10000000) {
+ return calculate;
+ } else {
+ console.log('result2', result2);
+ return null;
+ }
+}
scheduleCallback(calculate);
+scheduleCallback(calculate2);
src\scheduler\src\Scheduler.js
+import { requestHostCallback, shouldYieldToHost as shouldYield } from './SchedulerHostConfig';
+//任务队列
+let taskQueue = [];
+let currentTask;
/**
* 调度一个工作
* @param {*} callback 要执行的工作
*/
function scheduleCallback(callback) {
+ //把此工作添加到任务队列中
+ taskQueue.push(callback);
+ //开始调度flushWork
+ requestHostCallback(flushWork);
}
+/**
+ * 清空任务队列
+ * @returns 队列中是否还有任务
+ */
+function flushWork() {
+ return workLoop();
+}
+/**
+ * 清空任务队列
+ * @returns 队列中是否还有任务
+ */
+function workLoop() {
+ //取出第一个任务
+ currentTask = taskQueue[0];
+ //如果任务存在
+ while (currentTask) {
+ //如果当前的时间片到期了,退出工作循环
+ if (shouldYield()) {
+ break;
+ }
+ //执行当前的工作
+ const continuationCallback = currentTask();
+ //如果返回函数说明任务尚未结束,下次还执行它
+ if (typeof continuationCallback === 'function') {
+ currentTask = continuationCallback;
+ } else {
+ //否则表示此任务执行结束,可以把此任务移除队列
+ taskQueue.shift();
+ }
+ //还取第一个任务
+ currentTask = taskQueue[0];
+ }
+ return currentTask;
+}
+
+export {
+ scheduleCallback,
+ shouldYield
+}
import {
scheduleCallback,
shouldYield,
+ ImmediatePriority,//-1
+ UserBlockingPriority,//250
+ NormalPriority,//5000
+ LowPriority,//10000
+ IdlePriority,//1073741823
} from "./scheduler";
let result = 0;
let i = 0;
/**
* 总任务
* @returns
*/
+function calculate(didTimeout) {
+ for (; i < 10000000 && (!shouldYield() || didTimeout); i++) {//7个0
result += 1;
}
if (result < 10000000) {
return calculate;
} else {
console.log('result', result);
return null;
}
}
let result2 = 0;
let i2 = 0;
+function calculate2(didTimeout) {
+ for (; i2 < 10000000 && (!shouldYield() || didTimeout); i2++) {
result2 += 1;
}
if (result2 < 10000000) {
return calculate2;
} else {
console.log('result2', result2);
return null;
}
}
+let result3 = 0;
+let i3 = 0;
+function calculate3(didTimeout) {
+ for (; i3 < 10000000 && (!shouldYield() || didTimeout); i3++) {
+ result3 += 1;
+ }
+ if (result3 < 10000000) {
+ return calculate3;
+ } else {
+ console.log('result3', result3);
+ return null;
+ }
+}
+scheduleCallback(ImmediatePriority, calculate);//-1
+scheduleCallback(LowPriority, calculate2);//10000
+scheduleCallback(UserBlockingPriority, calculate3);//250
src\scheduler\src\SchedulerHostConfig.js
//截止时间
let deadline = 0;
//当前正在调度执行的工作
let scheduledHostCallback = null;
//每帧的时间片
let yieldInterval = 5;
const channel = new MessageChannel();
channel.port1.onmessage = performWorkUntilDeadline;
/**
* 获取当前的时间戳
* @returns 当前的时间戳
*/
export function getCurrentTime() {
return performance.now();
}
/**
* 判断是否到达了本帧的截止时间
* @returns 是否需要暂停执行
*/
export function shouldYieldToHost() {
const currentTime = getCurrentTime();
return currentTime >= deadline;
};
/**
* 执行工作直到截止时间
*/
export function performWorkUntilDeadline() {
const currentTime = getCurrentTime();
//计算截止时间
deadline = currentTime + yieldInterval;
//执行工作
+ const hasMoreWork = scheduledHostCallback(currentTime);
//如果此工作还没有执行完,则再次调度
if (hasMoreWork) {
channel.port2.postMessage(null);
}
}
/**
* 请求宿主的回调函数执行
* @param {*} callback
*/
export function requestHostCallback(callback) {
scheduledHostCallback = callback;
channel.port2.postMessage(null);
};
src\scheduler\src\Scheduler.js
+import { requestHostCallback, shouldYieldToHost as shouldYield, getCurrentTime } from './+SchedulerHostConfig';
+import { push, pop, peek } from './SchedulerMinHeap';
+import { ImmediatePriority, UserBlockingPriority, NormalPriority, LowPriority, IdlePriority } from './SchedulerPriorities';
+// 不同优先级对应的不同的任务过期时间间隔
+let maxSigned31BitInt = 1073741823;
+let IMMEDIATE_PRIORITY_TIMEOUT = -1;//立即执行的优先级,级别最高
+let USER_BLOCKING_PRIORITY_TIMEOUT = 250;//用户阻塞级别的优先级
+let NORMAL_PRIORITY_TIMEOUT = 5000;//正常的优先级
+let LOW_PRIORITY_TIMEOUT = 10000;//较低的优先级
+let IDLE_PRIORITY_TIMEOUT = maxSigned31BitInt;//优先级最低,表示任务可以闲置
//任务队列
let taskQueue = [];
let currentTask;
+//下一个任务ID编号
+let taskIdCounter = 1;
/**
* 调度一个工作
* @param {*} callback 要执行的工作
*/
+function scheduleCallback(priorityLevel, callback) {
+ // 获取当前时间,它是计算任务开始时间、过期时间和判断任务是否过期的依据
+ let currentTime = getCurrentTime();
+ // 确定任务开始时间
+ let startTime = currentTime;
+ // 计算过期时间
+ let timeout;
+ switch (priorityLevel) {
+ case ImmediatePriority://1
+ timeout = IMMEDIATE_PRIORITY_TIMEOUT;//-1
+ break;
+ case UserBlockingPriority://2
+ timeout = USER_BLOCKING_PRIORITY_TIMEOUT;//250
+ break;
+ case IdlePriority://5
+ timeout = IDLE_PRIORITY_TIMEOUT;//1073741823
+ break;
+ case LowPriority://4
+ timeout = LOW_PRIORITY_TIMEOUT;//10000
+ break;
+ case NormalPriority://3
+ default:
+ timeout = NORMAL_PRIORITY_TIMEOUT;//5000
+ break;
+ }
+ //计算超时时间
+ let expirationTime = startTime + timeout;
+ //创建新任务
+ let newTask = {
+ id: taskIdCounter++,//任务ID
+ callback,//真正的任务函数
+ priorityLevel,//任务优先级,参与计算任务过期时间
+ expirationTime,//表示任务何时过期,影响它在taskQueue中的排序
+ //为小顶堆的队列提供排序依据
+ sortIndex: -1
+ };
+ newTask.sortIndex = expirationTime;
+ //把此工作添加到任务队列中
+ push(taskQueue, newTask);
+ //开始调度flushWork
+ requestHostCallback(flushWork);
+}
/**
* 清空任务队列
* @returns 队列中是否还有任务
*/
+function flushWork(initialTime) {
+ return workLoop(initialTime);
+}
/**
* 清空任务队列
* @returns 队列中是否还有任务
*/
+function workLoop(initialTime) {
+ //当前时间
+ let currentTime = initialTime;
+ //取出第一个任务
+ currentTask = peek(taskQueue);
+ //如果任务存在
+ while (currentTask) {
+ //如果当前任务的过期时间大于当前时间,并且当前的时间片到期了,退出工作循环
+ if (currentTask.expirationTime > currentTime && shouldYield()) {
+ break;
+ }
+ //执行当前的工作
+ //const continuationCallback = currentTask();
+ const callback = currentTask.callback;
+ if (typeof callback === 'function') {
+ currentTask.callback = null;
+ const didUserCallbackTimeout = currentTask.expirationTime <= currentTime;
+ const continuationCallback = callback(didUserCallbackTimeout);
+ //如果返回函数说明任务尚未结束,下次还执行它
+ if (typeof continuationCallback === 'function') {
+ //currentTask = continuationCallback;
+ currentTask.callback = continuationCallback;
+ } else {
+ //否则表示此任务执行结束,可以把此任务移除队列
+ //taskQueue.shift();
+ pop(taskQueue);
+ }
+ } else {
+ pop(taskQueue);
+ }
+ //还取第一个任务
+ currentTask = peek(taskQueue);
+ }
+ return currentTask;
+}
export {
scheduleCallback,
shouldYield,
+ ImmediatePriority,
+ UserBlockingPriority,
+ NormalPriority,
+ IdlePriority,
+ LowPriority
}
src\scheduler\src\SchedulerPriorities.js
export const NoPriority = 0; // 没有任何优先级
export const ImmediatePriority = 1; // 立即执行的优先级,级别最高
export const UserBlockingPriority = 2; // 用户阻塞级别的优先级
export const NormalPriority = 3; // 正常的优先级
export const LowPriority = 4; // 较低的优先级
export const IdlePriority = 5; // 优先级最低,表示任务可以闲置
src\scheduler\src\SchedulerMinHeap.js
export function push(heap, node) {
const index = heap.length;
heap.push(node);
siftUp(heap, node, index);
}
export function peek(heap) {
const first = heap[0];
return first === undefined ? null : first;
}
export function pop(heap) {
const first = heap[0];
if (first !== undefined) {
const last = heap.pop();
if (last !== first) {
heap[0] = last;
siftDown(heap, last, 0);
}
return first;
} else {
return null;
}
}
function siftUp(heap, node, i) {
let index = i;
while (true) {
const parentIndex = index - 1 >>> 1;
const parent = heap[parentIndex];
if (parent !== undefined && compare(parent, node) > 0) {
heap[parentIndex] = node;
heap[index] = parent;
index = parentIndex;
} else {
return;
}
}
}
function siftDown(heap, node, i) {
let index = i;
const length = heap.length;
while (index < length) {
const leftIndex = (index + 1) * 2 - 1;
const left = heap[leftIndex];
const rightIndex = leftIndex + 1;
const right = heap[rightIndex];
if (left !== undefined && compare(left, node) < 0) {
if (right !== undefined && compare(right, left) < 0) {
heap[index] = right;
heap[rightIndex] = node;
index = rightIndex;
} else {
heap[index] = left;
heap[leftIndex] = node;
index = leftIndex;
}
} else if (right !== undefined && compare(right, node) < 0) {
heap[index] = right;
heap[rightIndex] = node;
index = rightIndex;
} else {
return;
}
}
}
function compare(a, b) {
const diff = a.sortIndex - b.sortIndex;
return diff !== 0 ? diff : a.id - b.id;
}
import {
scheduleCallback,
shouldYield,
ImmediatePriority,//-1
UserBlockingPriority,//250
NormalPriority,//5000
LowPriority,//10000
IdlePriority,//1073741823
} from "./scheduler";
let result = 0;
let i = 0;
/**
* 总任务
* @returns
*/
function calculate(didTimeout) {
for (; i < 10000000 && (!shouldYield() || didTimeout); i++) {//7个0
result += 1;
}
if (result < 10000000) {
return calculate;
} else {
console.log('result', result);
return null;
}
}
let result2 = 0;
let i2 = 0;
+console.time('cost');
function calculate2(didTimeout) {
+ if (i2 === 0)
+ console.timeEnd('cost');
for (; i2 < 10000000 && (!shouldYield() || didTimeout); i2++) {
result2 += 1;
}
if (result2 < 10000000) {
return calculate2;
} else {
console.log('result2', result2);
return null;
}
}
scheduleCallback(ImmediatePriority, calculate);//-1
+scheduleCallback(LowPriority, calculate2, { delay: 10000 });//10000
src\scheduler\src\SchedulerHostConfig.js
//截止时间
let deadline = 0;
//当前正在调度执行的工作
let scheduledHostCallback = null;
//每帧的时间片
let yieldInterval = 5;
+let taskTimeoutID = -1;
const channel = new MessageChannel();
channel.port1.onmessage = performWorkUntilDeadline;
/**
* 获取当前的时间戳
* @returns 当前的时间戳
*/
export function getCurrentTime() {
return performance.now();
}
/**
* 判断是否到达了本帧的截止时间
* @returns 是否需要暂停执行
*/
export function shouldYieldToHost() {
const currentTime = getCurrentTime();
return currentTime >= deadline;
};
/**
* 执行工作直到截止时间
*/
export function performWorkUntilDeadline() {
const currentTime = getCurrentTime();
//计算截止时间
deadline = currentTime + yieldInterval;
//执行工作
const hasMoreWork = scheduledHostCallback(currentTime);
//如果此工作还没有执行完,则再次调度
if (hasMoreWork) {
channel.port2.postMessage(null);
}
}
/**
* 请求宿主的回调函数执行
* @param {*} callback
*/
export function requestHostCallback(callback) {
scheduledHostCallback = callback;
channel.port2.postMessage(null);
};
+export function requestHostTimeout(callback, ms) {
+ taskTimeoutID = setTimeout(() => {
+ callback(getCurrentTime());
+ }, ms);
+};
src\scheduler\src\Scheduler.js
+import { requestHostCallback, shouldYieldToHost as shouldYield, getCurrentTime, requestHostTimeout } from './SchedulerHostConfig';
import { push, pop, peek } from './SchedulerMinHeap';
import { ImmediatePriority, UserBlockingPriority, NormalPriority, LowPriority, IdlePriority } from './SchedulerPriorities';
// 不同优先级对应的不同的任务过期时间间隔
let maxSigned31BitInt = 1073741823;
let IMMEDIATE_PRIORITY_TIMEOUT = -1;//立即执行的优先级,级别最高
let USER_BLOCKING_PRIORITY_TIMEOUT = 250;//用户阻塞级别的优先级
let NORMAL_PRIORITY_TIMEOUT = 5000;//正常的优先级
let LOW_PRIORITY_TIMEOUT = 10000;//较低的优先级
let IDLE_PRIORITY_TIMEOUT = maxSigned31BitInt;//优先级最低,表示任务可以闲置
//已经可以开始执行队列
let taskQueue = [];
+//尚未可以开始执行队列
+let timerQueue = [];
let currentTask;
//下一个任务ID编号
let taskIdCounter = 1;
/**
* 调度一个工作
* @param {*} callback 要执行的工作
*/
+function scheduleCallback(priorityLevel, callback, options) {
// 获取当前时间,它是计算任务开始时间、过期时间和判断任务是否过期的依据
let currentTime = getCurrentTime();
// 确定任务开始时间
+ let 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;
+ }
// 计算过期时间
let timeout;
switch (priorityLevel) {
case ImmediatePriority://1
timeout = IMMEDIATE_PRIORITY_TIMEOUT;//-1
break;
case UserBlockingPriority://2
timeout = USER_BLOCKING_PRIORITY_TIMEOUT;//250
break;
case IdlePriority://5
timeout = IDLE_PRIORITY_TIMEOUT;//1073741823
break;
case LowPriority://4
timeout = LOW_PRIORITY_TIMEOUT;//10000
break;
case NormalPriority://3
default:
timeout = NORMAL_PRIORITY_TIMEOUT;//5000
break;
}
//计算超时时间
let expirationTime = startTime + timeout;
//创建新任务
let newTask = {
id: taskIdCounter++,//任务ID
callback,//真正的任务函数
priorityLevel,//任务优先级,参与计算任务过期时间
+ startTime,
expirationTime,//表示任务何时过期,影响它在taskQueue中的排序
//为小顶堆的队列提供排序依据
sortIndex: -1
};
+ if (startTime > currentTime) {
+ newTask.sortIndex = startTime;
+ push(timerQueue, newTask);
+ if (peek(taskQueue) === null && newTask === peek(timerQueue)) {
+ requestHostTimeout(handleTimeout, startTime - currentTime);
+ }
+ } else {
newTask.sortIndex = expirationTime;
//把此工作添加到任务队列中
push(taskQueue, newTask);
//开始调度flushWork
requestHostCallback(flushWork);
+ }
}
+/**
+ * 处理超时任务
+ * @param {*} currentTime
+ */
+function handleTimeout(currentTime) {
+ advanceTimers(currentTime);
+ if (peek(taskQueue) !== null) {
+ requestHostCallback(flushWork);
+ } else {
+ const firstTimer = peek(timerQueue);
+ if (firstTimer !== null) {
+ requestHostTimeout(handleTimeout, firstTimer.startTime - currentTime);
+ }
+ }
+}
+function advanceTimers(currentTime) {
+ let timer = peek(timerQueue);
+ while (timer !== null) {
+ if (timer.callback === null) {
+ pop(timerQueue);
+ } else if (timer.startTime <= currentTime) {
+ pop(timerQueue);
+ timer.sortIndex = timer.expirationTime;
+ push(taskQueue, timer);
+ } else {
+ return;
+ }
+ timer = peek(timerQueue);
+ }
+}
/**
* 清空任务队列
* @returns 队列中是否还有任务
*/
function flushWork(initialTime) {
return workLoop(initialTime);
}
/**
* 清空任务队列
* @returns 队列中是否还有任务
*/
function workLoop(initialTime) {
//当前时间
let currentTime = initialTime;
//取出第一个任务
currentTask = peek(taskQueue);
//如果任务存在
while (currentTask) {
//如果当前任务的过期时间大于当前时间,并且当前的时间片到期了,退出工作循环
if (currentTask.expirationTime > currentTime && shouldYield()) {
break;
}
//执行当前的工作
//const continuationCallback = currentTask();
const callback = currentTask.callback;
if (typeof callback === 'function') {
currentTask.callback = null;
const didUserCallbackTimeout = currentTask.expirationTime <= currentTime;
const continuationCallback = callback(didUserCallbackTimeout);
//如果返回函数说明任务尚未结束,下次还执行它
if (typeof continuationCallback === 'function') {
//currentTask = continuationCallback;
currentTask.callback = continuationCallback;
} else {
//否则表示此任务执行结束,可以把此任务移除队列
//taskQueue.shift();
pop(taskQueue);
}
} else {
pop(taskQueue);
}
//还取第一个任务
currentTask = peek(taskQueue);
}
+ if (currentTask !== null) {
+ return true;
+ } else {
+ const firstTimer = peek(timerQueue);
+ if (firstTimer !== null) {
+ requestHostTimeout(handleTimeout, firstTimer.startTime - currentTime);
+ }
+ return false;
+ }
}
export {
scheduleCallback,
shouldYield,
ImmediatePriority,
UserBlockingPriority,
NormalPriority,
IdlePriority,
LowPriority
}
src\index.js
import {
scheduleCallback,
shouldYield,
ImmediatePriority,//-1
UserBlockingPriority,//250
NormalPriority,//5000
LowPriority,//10000
IdlePriority,//1073741823
+ cancelCallback
} from "./scheduler";
let result = 0;
let i = 0;
/**
* 总任务
* @returns
*/
function calculate(didTimeout) {
for (; i < 10000000 && (!shouldYield() || didTimeout); i++) {//7个0
result += 1;
}
if (result < 10000000) {
return calculate;
} else {
console.log('result', result);
return null;
}
}
let result2 = 0;
let i2 = 0;
console.time('cost');
function calculate2(didTimeout) {
if (i2 === 0)
console.timeEnd('cost');
for (; i2 < 10000000 && (!shouldYield() || didTimeout); i2++) {
result2 += 1;
}
if (result2 < 10000000) {
return calculate2;
} else {
console.log('result2', result2);
return null;
}
}
scheduleCallback(ImmediatePriority, calculate);//-1
+const task = scheduleCallback(LowPriority, calculate2, { delay: 10000 });//10000
+cancelCallback(task);
src\scheduler\src\Scheduler.js
import { requestHostCallback, shouldYieldToHost as shouldYield, getCurrentTime, requestHostTimeout } from './SchedulerHostConfig';
import { push, pop, peek } from './SchedulerMinHeap';
import { ImmediatePriority, UserBlockingPriority, NormalPriority, LowPriority, IdlePriority } from './SchedulerPriorities';
// 不同优先级对应的不同的任务过期时间间隔
let maxSigned31BitInt = 1073741823;
let IMMEDIATE_PRIORITY_TIMEOUT = -1;//立即执行的优先级,级别最高
let USER_BLOCKING_PRIORITY_TIMEOUT = 250;//用户阻塞级别的优先级
let NORMAL_PRIORITY_TIMEOUT = 5000;//正常的优先级
let LOW_PRIORITY_TIMEOUT = 10000;//较低的优先级
let IDLE_PRIORITY_TIMEOUT = maxSigned31BitInt;//优先级最低,表示任务可以闲置
//已经可以开始执行队列
let taskQueue = [];
//尚未可以开始执行队列
let timerQueue = [];
let currentTask;
//下一个任务ID编号
let taskIdCounter = 1;
/**
* 调度一个工作
* @param {*} callback 要执行的工作
*/
function scheduleCallback(priorityLevel, callback, options) {
// 获取当前时间,它是计算任务开始时间、过期时间和判断任务是否过期的依据
let currentTime = getCurrentTime();
// 确定任务开始时间
let 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;
}
// 计算过期时间
let timeout;
switch (priorityLevel) {
case ImmediatePriority://1
timeout = IMMEDIATE_PRIORITY_TIMEOUT;//-1
break;
case UserBlockingPriority://2
timeout = USER_BLOCKING_PRIORITY_TIMEOUT;//250
break;
case IdlePriority://5
timeout = IDLE_PRIORITY_TIMEOUT;//1073741823
break;
case LowPriority://4
timeout = LOW_PRIORITY_TIMEOUT;//10000
break;
case NormalPriority://3
default:
timeout = NORMAL_PRIORITY_TIMEOUT;//5000
break;
}
//计算超时时间
let expirationTime = startTime + timeout;
//创建新任务
let newTask = {
id: taskIdCounter++,//任务ID
callback,//真正的任务函数
priorityLevel,//任务优先级,参与计算任务过期时间
startTime,
expirationTime,//表示任务何时过期,影响它在taskQueue中的排序
//为小顶堆的队列提供排序依据
sortIndex: -1
};
if (startTime > currentTime) {
newTask.sortIndex = startTime;
push(timerQueue, newTask);
if (peek(taskQueue) === null && newTask === peek(timerQueue)) {
requestHostTimeout(handleTimeout, startTime - currentTime);
}
} else {
newTask.sortIndex = expirationTime;
//把此工作添加到任务队列中
push(taskQueue, newTask);
//开始调度flushWork
requestHostCallback(flushWork);
}
+ return newTask;
}
/**
* 处理超时任务
* @param {*} currentTime
*/
function handleTimeout(currentTime) {
advanceTimers(currentTime);
if (peek(taskQueue) !== null) {
requestHostCallback(flushWork);
} else {
const firstTimer = peek(timerQueue);
if (firstTimer !== null) {
requestHostTimeout(handleTimeout, firstTimer.startTime - currentTime);
}
}
}
function advanceTimers(currentTime) {
let timer = peek(timerQueue);
while (timer !== null) {
if (timer.callback === null) {
pop(timerQueue);
} else if (timer.startTime <= currentTime) {
pop(timerQueue);
timer.sortIndex = timer.expirationTime;
push(taskQueue, timer);
} else {
return;
}
timer = peek(timerQueue);
}
}
/**
* 清空任务队列
* @returns 队列中是否还有任务
*/
function flushWork(initialTime) {
return workLoop(initialTime);
}
/**
* 清空任务队列
* @returns 队列中是否还有任务
*/
function workLoop(initialTime) {
//当前时间
let currentTime = initialTime;
//取出第一个任务
currentTask = peek(taskQueue);
//如果任务存在
while (currentTask) {
//如果当前任务的过期时间大于当前时间,并且当前的时间片到期了,退出工作循环
if (currentTask.expirationTime > currentTime && shouldYield()) {
break;
}
//执行当前的工作
//const continuationCallback = currentTask();
const callback = currentTask.callback;
if (typeof callback === 'function') {
currentTask.callback = null;
const didUserCallbackTimeout = currentTask.expirationTime <= currentTime;
const continuationCallback = callback(didUserCallbackTimeout);
//如果返回函数说明任务尚未结束,下次还执行它
if (typeof continuationCallback === 'function') {
//currentTask = continuationCallback;
currentTask.callback = continuationCallback;
} else {
//否则表示此任务执行结束,可以把此任务移除队列
//taskQueue.shift();
pop(taskQueue);
}
} else {
pop(taskQueue);
}
//还取第一个任务
currentTask = peek(taskQueue);
}
if (currentTask !== null) {
return true;
} else {
const firstTimer = peek(timerQueue);
if (firstTimer !== null) {
requestHostTimeout(handleTimeout, firstTimer.startTime - currentTime);
}
return false;
}
}
+export function cancelCallback(task) {
+ //清空回调以表示任务已取消
+ //无法从队列中删除,因为无法从基于数组的堆中删除任意节点,只能删除第一个节点
+ task.callback = null;
+}
export {
scheduleCallback,
shouldYield,
ImmediatePriority,
UserBlockingPriority,
NormalPriority,
IdlePriority,
LowPriority,
+ cancelCallback
}