Vue3系列之effect和ReactiveEffect track trigger源码解析

const targetMap = new WeakMap<any, KeyToDepMap>()
export let activeEffect: ReactiveEffect | undefined
export let shouldTrack = true
const trackStack: boolean[] = []

// 暂停收集
export function pauseTracking() {
trackStack.push(shouldTrack)
shouldTrack = false
}
// 恢复收集
export function enableTracking() {
trackStack.push(shouldTrack)
shouldTrack = true
}
// 重置为上一次的状态
export function resetTracking() {
const last = trackStack.pop()
shouldTrack = last === undefined ? true : last
}

export class ReactiveEffect<T = any> {
active = true
deps: Dep[] = []
parent: ReactiveEffect | undefined = undefined
/**
* Can be attached after creation
* @internal
*/
computed?: ComputedRefImpl<T>
/**
* @internal
*/
allowRecurse?: boolean
/**
* @internal
*/
private deferStop?: boolean
onStop?: () => void
// dev only
onTrack?: (event: DebuggerEvent) => void
// dev only
onTrigger?: (event: DebuggerEvent) => void
constructor(
public fn: () => T,
public scheduler: EffectScheduler | null = null,
scope?: EffectScope
) {
recordEffectScope(this, scope)
}
run() {
if (!this.active) {
return this.fn()
}
// 当前活跃的effect
let parent: ReactiveEffect | undefined = activeEffect
let lastShouldTrack = shouldTrack
// 如果当前活跃的effect就是这个effect本身，则直接返回
while (parent) {
if (parent === this) {
return
}
parent = parent.parent
}
// 依次活跃的effect形成链表，由parent属性连接
try {
this.parent = activeEffect
activeEffect = this
shouldTrack = true
trackOpBit = 1 << ++effectTrackDepth
if (effectTrackDepth <= maxMarkerBits) {
// 遍历 this.deps 将其中的effect设置为已捕获 tracked
initDepMarkers(this)
} else {
// 层级溢出则清除当前副作用
cleanupEffect(this)
}
// 尾调用传入的fn
return this.fn()
} finally {
// 因为前面有return，因此当 try 的代码块发生异常时执行
if (effectTrackDepth <= maxMarkerBits) {
// 该方法遍历 this.deps，将其中过气的effect删除，未捕获的effect加入
// effect 就是其中的 dep
finalizeDepMarkers(this)
}
trackOpBit = 1 << --effectTrackDepth
// 复原一些状态
activeEffect = this.parent
shouldTrack = lastShouldTrack
this.parent = undefined
// 若设置了延迟停止，则执行stop，进行延迟清理
if (this.deferStop) {
this.stop()
}
}
}
// 清除副作用
stop() {
// stopped while running itself - defer the cleanup
if (activeEffect === this) {
this.deferStop = true
} else if (this.active) {
cleanupEffect(this)
if (this.onStop) {
this.onStop()
}
this.active = false
}
}
}

function cleanupEffect(effect: ReactiveEffect) {
const { deps } = effect
if (deps.length) {
for (let i = 0; i < deps.length; i++) {
deps[i].delete(effect)
}
deps.length = 0
}
}

export interface DebuggerOptions {
onTrack?: (event: DebuggerEvent) => void
onTrigger?: (event: DebuggerEvent) => void
}
export interface ReactiveEffectOptions extends DebuggerOptions {
lazy?: boolean
scheduler?: EffectScheduler
scope?: EffectScope
allowRecurse?: boolean
onStop?: () => void
}
export interface ReactiveEffectRunner<T = any> {
(): T
effect: ReactiveEffect
}

export function effect<T = any>(
fn: () => T,
options?: ReactiveEffectOptions
): ReactiveEffectRunner {
// 处理fn
if ((fn as ReactiveEffectRunner).effect) {
fn = (fn as ReactiveEffectRunner).effect.fn
}
// 根据 fn 创建一个 _effect
const _effect = new ReactiveEffect(fn)
if (options) {
// 用 options 覆盖 _effect 上的属性
extend(_effect, options)
if (options.scope) recordEffectScope(_effect, options.scope)
}
// 没有 lazy , 则 _effect 立即执行一次 run()
if (!options || !options.lazy) {
_effect.run()
}
// runner：拿到 _effect.run 并挂上 effect 属性，包装成 ReactiveEffectRunner 类型
const runner = _effect.run.bind(_effect) as ReactiveEffectRunner
// effect属性指回 _effect 自身，方便使用 runner 调用 run 和 stop
runner.effect = _effect
// 返回 runner
return runner
}

export function stop(runner: ReactiveEffectRunner) {
runner.effect.stop()
}

// 全局变量 targetMap
const targetMap = new WeakMap<any, KeyToDepMap>()
export function track(target: object, type: TrackOpTypes, key: unknown) {
if (shouldTrack && activeEffect) {
let depsMap = targetMap.get(target)
if (!depsMap) {
targetMap.set(target, (depsMap = new Map()))
}
let dep = depsMap.get(key)
if (!dep) {
depsMap.set(key, (dep = createDep()))
}
const eventInfo = __DEV__
? { effect: activeEffect, target, type, key }
: undefined
trackEffects(dep, eventInfo)
}
}

export const createDep = (effects?: ReactiveEffect[]): Dep => {
const dep = new Set<ReactiveEffect>(effects) as Dep
dep.w = 0
dep.n = 0
return dep
}

export function trackEffects(
dep: Dep,
debuggerEventExtraInfo?: DebuggerEventExtraInfo
) {
let shouldTrack = false
if (effectTrackDepth <= maxMarkerBits) {
if (!newTracked(dep)) {
dep.n |= trackOpBit // set newly tracked
shouldTrack = !wasTracked(dep)
}
} else {
// Full cleanup mode.
shouldTrack = !dep.has(activeEffect!)
}
// 当前依赖 dep 还未被捕获 / 当前依赖 dep 中，还没有当前活跃的副作用时，
// 将当前活跃的副作用 effect 添加进 dep 里，同时在把 dep 加入受副作用影响的依赖集合 activeEffect.deps 中
if (shouldTrack) {
dep.add(activeEffect!)
activeEffect!.deps.push(dep)
if (__DEV__ && activeEffect!.onTrack) {
activeEffect!.onTrack({
effect: activeEffect!,
...debuggerEventExtraInfo!
})
}
}
}

function triggerEffect(
effect: ReactiveEffect,
debuggerEventExtraInfo?: DebuggerEventExtraInfo
) {
if (effect !== activeEffect || effect.allowRecurse) {
if (__DEV__ && effect.onTrigger) {
effect.onTrigger(extend({ effect }, debuggerEventExtraInfo))
}
// 实际触发更新的地方
if (effect.scheduler) {
effect.scheduler()
} else {
effect.run()
}
}
}

export function triggerEffects(
dep: Dep | ReactiveEffect[],
debuggerEventExtraInfo?: DebuggerEventExtraInfo
) {
// spread into array for stabilization
const effects = isArray(dep) ? dep : [...dep]
// 两者互斥，但是执行的操作相同？而且为什么不写在一个 for...of... 里 ？
for (const effect of effects) {
if (effect.computed) {
triggerEffect(effect, debuggerEventExtraInfo)
}
}
for (const effect of effects) {
if (!effect.computed) {
triggerEffect(effect, debuggerEventExtraInfo)
}
}
}

export function trigger(
target: object,
type: TriggerOpTypes,
key?: unknown,
newValue?: unknown,
oldValue?: unknown,
oldTarget?: Map<unknown, unknown> | Set<unknown>
) {
const depsMap = targetMap.get(target)
if (!depsMap) {
// never been tracked
return
}
// 用于聚集所有相关依赖
let deps: (Dep | undefined)[] = []
if (type === TriggerOpTypes.CLEAR) {
// 调用了Set、Map实例的clear方法，将触发全部相关的副作用
// collection being cleared
// trigger all effects for target
deps = [...depsMap.values()]
} else if (key === 'length' && isArray(target)) {
// 目标对象是数组，且修改了length属性时，会触发全部相关的副作用
depsMap.forEach((dep, key) => {
if (key === 'length' || key >= (newValue as number)) {
deps.push(dep)
}
})
} else {
// schedule runs for SET | ADD | DELETE
if (key !== void 0) {
deps.push(depsMap.get(key))
}
// also run for iteration key on ADD | DELETE | Map.SET
switch (type) {
case TriggerOpTypes.ADD:
if (!isArray(target)) {
deps.push(depsMap.get(ITERATE_KEY))
if (isMap(target)) {
deps.push(depsMap.get(MAP_KEY_ITERATE_KEY))
}
} else if (isIntegerKey(key)) {
// 数组下标成员的更改 会引起 length 属性相关的更新
// new index added to array -> length changes
deps.push(depsMap.get('length'))
}
break
case TriggerOpTypes.DELETE:
if (!isArray(target)) {
deps.push(depsMap.get(ITERATE_KEY))
if (isMap(target)) {
deps.push(depsMap.get(MAP_KEY_ITERATE_KEY))
}
}
break
case TriggerOpTypes.SET:
if (isMap(target)) {
deps.push(depsMap.get(ITERATE_KEY))
}
break
}
}
const eventInfo = __DEV__
? { target, type, key, newValue, oldValue, oldTarget }
: undefined
if (deps.length === 1) {
if (deps[0]) {
if (__DEV__) {
triggerEffects(deps[0], eventInfo)
} else {
triggerEffects(deps[0])
}
}
} else {
const effects: ReactiveEffect[] = []
for (const dep of deps) {
if (dep) {
effects.push(...dep)
}
}
// 这里triggerEffects接受的参数类型为Set，之前的是数组
if (__DEV__) {
triggerEffects(createDep(effects), eventInfo)
} else {
triggerEffects(createDep(effects))
}
}
}