perf(reactivity): improve reactive effect memory usage (#4001)

Based on #2345 , but with smaller API change

- Use class implementation for `ReactiveEffect`
- Switch internal creation of effects to use the class constructor
- Avoid options object allocation
- Avoid creating bound effect runner function (used in schedulers) when not necessary.
- Consumes ~17% less memory compared to last commit
- Introduces a very minor breaking change: the `scheduler` option passed to `effect` no longer receives the runner function.

packages/reactivity/src/computed.ts

@@ -1,4 +1,4 @@
-import { effect, ReactiveEffect } from './effect'
+import { ReactiveEffect } from './effect'
 import { Ref, trackRefValue, triggerRefValue } from './ref'
 import { isFunction, NOOP } from '@vue/shared'
 import { ReactiveFlags, toRaw } from './reactive'
@@ -35,16 +35,12 @@ class ComputedRefImpl<T> {
     private readonly _setter: ComputedSetter<T>,
     isReadonly: boolean
   ) {
-    this.effect = effect(getter, {
-      lazy: true,
-      scheduler: () => {
-        if (!this._dirty) {
-          this._dirty = true
-          triggerRefValue(this)
-        }
+    this.effect = new ReactiveEffect(getter, () => {
+      if (!this._dirty) {
+        this._dirty = true
+        triggerRefValue(this)
       }
     })
-
     this[ReactiveFlags.IS_READONLY] = isReadonly
   }
 
@@ -52,10 +48,10 @@ class ComputedRefImpl<T> {
     // the computed ref may get wrapped by other proxies e.g. readonly() #3376
     const self = toRaw(this)
     if (self._dirty) {
-      self._value = this.effect()
+      self._value = self.effect.run()!
       self._dirty = false
     }
-    trackRefValue(this)
+    trackRefValue(self)
     return self._value
   }
 

packages/reactivity/src/effect.ts

@@ -1,5 +1,5 @@
 import { TrackOpTypes, TriggerOpTypes } from './operations'
-import { EMPTY_OBJ, extend, isArray, isIntegerKey, isMap } from '@vue/shared'
+import { extend, isArray, isIntegerKey, isMap } from '@vue/shared'
 
 // The main WeakMap that stores {target -> key -> dep} connections.
 // Conceptually, it's easier to think of a dependency as a Dep class
@@ -9,40 +9,7 @@ type Dep = Set<ReactiveEffect>
 type KeyToDepMap = Map<any, Dep>
 const targetMap = new WeakMap<any, KeyToDepMap>()
 
-export interface ReactiveEffect<T = any> {
-  (): T
-  _isEffect: true
-  id: number
-  active: boolean
-  raw: () => T
-  deps: Array<Dep>
-  options: ReactiveEffectOptions
-  allowRecurse: boolean
-}
-
-export interface ReactiveEffectOptions {
-  lazy?: boolean
-  scheduler?: (job: ReactiveEffect) => void
-  onTrack?: (event: DebuggerEvent) => void
-  onTrigger?: (event: DebuggerEvent) => void
-  onStop?: () => void
-  /**
-   * Indicates whether the job is allowed to recursively trigger itself when
-   * managed by the scheduler.
-   *
-   * By default, a job cannot trigger itself because some built-in method calls,
-   * e.g. Array.prototype.push actually performs reads as well (#1740) which
-   * can lead to confusing infinite loops.
-   * The allowed cases are component update functions and watch callbacks.
-   * Component update functions may update child component props, which in turn
-   * trigger flush: "pre" watch callbacks that mutates state that the parent
-   * relies on (#1801). Watch callbacks doesn't track its dependencies so if it
-   * triggers itself again, it's likely intentional and it is the user's
-   * responsibility to perform recursive state mutation that eventually
-   * stabilizes (#1727).
-   */
-  allowRecurse?: boolean
-}
+export type EffectScheduler = () => void
 
 export type DebuggerEvent = {
   effect: ReactiveEffect
@@ -62,52 +29,34 @@ let activeEffect: ReactiveEffect | undefined
 
 export const ITERATE_KEY = Symbol(__DEV__ ? 'iterate' : '')
 export const MAP_KEY_ITERATE_KEY = Symbol(__DEV__ ? 'Map key iterate' : '')
+export class ReactiveEffect<T = any> {
+  active = true
+  deps: Dep[] = []
 
-export function isEffect(fn: any): fn is ReactiveEffect {
-  return fn && fn._isEffect === true
-}
+  // can be attached after creation
+  onStop?: () => void
+  // dev only
+  onTrack?: (event: DebuggerEvent) => void
+  // dev only
+  onTrigger?: (event: DebuggerEvent) => void
 
-export function effect<T = any>(
-  fn: () => T,
-  options: ReactiveEffectOptions = EMPTY_OBJ
-): ReactiveEffect<T> {
-  if (isEffect(fn)) {
-    fn = fn.raw
-  }
-  const effect = createReactiveEffect(fn, options)
-  if (!options.lazy) {
-    effect()
-  }
-  return effect
-}
+  constructor(
+    public fn: () => T,
+    public scheduler: EffectScheduler | null = null,
+    // allow recursive self-invocation
+    public allowRecurse = false
+  ) {}
 
-export function stop(effect: ReactiveEffect) {
-  if (effect.active) {
-    cleanup(effect)
-    if (effect.options.onStop) {
-      effect.options.onStop()
+  run() {
+    if (!this.active) {
+      return this.fn()
     }
-    effect.active = false
-  }
-}
-
-let uid = 0
-
-function createReactiveEffect<T = any>(
-  fn: () => T,
-  options: ReactiveEffectOptions
-): ReactiveEffect<T> {
-  const effect = function reactiveEffect(): unknown {
-    if (!effect.active) {
-      return fn()
-    }
-    if (!effectStack.includes(effect)) {
-      cleanup(effect)
+    if (!effectStack.includes(this)) {
+      this.cleanup()
       try {
         enableTracking()
-        effectStack.push(effect)
-        activeEffect = effect
-        return fn()
+        effectStack.push((activeEffect = this))
+        return this.fn()
       } finally {
         effectStack.pop()
         resetTracking()
@@ -115,25 +64,65 @@ function createReactiveEffect<T = any>(
         activeEffect = n > 0 ? effectStack[n - 1] : undefined
       }
     }
-  } as ReactiveEffect
-  effect.id = uid++
-  effect.allowRecurse = !!options.allowRecurse
-  effect._isEffect = true
-  effect.active = true
-  effect.raw = fn
-  effect.deps = []
-  effect.options = options
-  return effect
+  }
+
+  cleanup() {
+    const { deps } = this
+    if (deps.length) {
+      for (let i = 0; i < deps.length; i++) {
+        deps[i].delete(this)
+      }
+      deps.length = 0
+    }
+  }
+
+  stop() {
+    if (this.active) {
+      this.cleanup()
+      if (this.onStop) {
+        this.onStop()
+      }
+      this.active = false
+    }
+  }
 }
 
-function cleanup(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 ReactiveEffectOptions {
+  lazy?: boolean
+  scheduler?: EffectScheduler
+  allowRecurse?: boolean
+  onStop?: () => void
+  onTrack?: (event: DebuggerEvent) => void
+  onTrigger?: (event: DebuggerEvent) => void
+}
+
+export interface ReactiveEffectRunner<T = any> {
+  (): T
+  effect: ReactiveEffect
+}
+
+export function effect<T = any>(
+  fn: () => T,
+  options?: ReactiveEffectOptions
+): ReactiveEffectRunner {
+  if ((fn as ReactiveEffectRunner).effect) {
+    fn = (fn as ReactiveEffectRunner).effect.fn
   }
+
+  const _effect = new ReactiveEffect(fn)
+  if (options) {
+    extend(_effect, options)
+  }
+  if (!options || !options.lazy) {
+    _effect.run()
+  }
+  const runner = _effect.run.bind(_effect) as ReactiveEffectRunner
+  runner.effect = _effect
+  return runner
+}
+
+export function stop(runner: ReactiveEffectRunner) {
+  runner.effect.stop()
 }
 
 let shouldTrack = true
@@ -185,8 +174,8 @@ export function trackEffects(
   if (!dep.has(activeEffect!)) {
     dep.add(activeEffect!)
     activeEffect!.deps.push(dep)
-    if (__DEV__ && activeEffect!.options.onTrack) {
-      activeEffect!.options.onTrack(
+    if (__DEV__ && activeEffect!.onTrack) {
+      activeEffect!.onTrack(
         Object.assign(
           {
             effect: activeEffect!
@@ -284,13 +273,13 @@ export function triggerEffects(
   // spread into array for stabilization
   for (const effect of [...dep]) {
     if (effect !== activeEffect || effect.allowRecurse) {
-      if (__DEV__ && effect.options.onTrigger) {
-        effect.options.onTrigger(extend({ effect }, debuggerEventExtraInfo))
+      if (__DEV__ && effect.onTrigger) {
+        effect.onTrigger(extend({ effect }, debuggerEventExtraInfo))
       }
-      if (effect.options.scheduler) {
-        effect.options.scheduler(effect)
+      if (effect.scheduler) {
+        effect.scheduler()
       } else {
-        effect()
+        effect.run()
       }
     }
   }

packages/reactivity/src/index.ts

@@ -46,7 +46,9 @@ export {
   resetTracking,
   ITERATE_KEY,
   ReactiveEffect,
+  ReactiveEffectRunner,
   ReactiveEffectOptions,
+  EffectScheduler,
   DebuggerEvent
 } from './effect'
 export { TrackOpTypes, TriggerOpTypes } from './operations'