Allow JIT fast-path on Cloudflare Workers when new Function is available (microtask approach) #5565
+92
−15
use microtasks for speedup
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,139 @@ | ||
| import { afterEach, beforeEach, describe, expect, test, vi } from "vitest"; | ||
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| const state = vi.hoisted(() => { | ||
| Object.defineProperty(globalThis, "navigator", { | ||
| value: { userAgent: "Cloudflare-Workers" }, | ||
| configurable: true, | ||
| writable: true, | ||
| }); | ||
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| const userAgent = typeof navigator === "undefined" ? undefined : navigator?.userAgent; | ||
| const isCloudflare = typeof userAgent === "string" && userAgent.includes("Cloudflare"); | ||
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| let _allowsEval: boolean; | ||
| try { | ||
| const F = Function; | ||
| new F(""); | ||
| _allowsEval = true; | ||
| } catch (_) { | ||
| _allowsEval = false; | ||
| } | ||
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| const valueBeforeMicrotask = _allowsEval; | ||
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| if (isCloudflare && _allowsEval) { | ||
| Promise.resolve().then(() => { | ||
| _allowsEval = false; | ||
| }); | ||
| } | ||
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| return { | ||
| isCloudflare, | ||
| valueBeforeMicrotask, | ||
| getAllowsEval: () => _allowsEval, | ||
| }; | ||
| }); | ||
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| describe("Cloudflare JIT microtask timing", () => { | ||
| test("allowsEval is true during sync, false after microtask", () => { | ||
| expect(state.isCloudflare).toBe(true); | ||
| expect(state.valueBeforeMicrotask).toBe(true); | ||
| expect(state.getAllowsEval()).toBe(false); | ||
| }); | ||
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| test("util.allowsEval is false after module load", async () => { | ||
| vi.resetModules(); | ||
| const { allowsEval } = await import("../../core/util.js"); | ||
| expect(allowsEval.value).toBe(false); | ||
| }); | ||
| }); | ||
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| describe("Cloudflare allowsEval behavior", () => { | ||
| let navigatorDescriptor: PropertyDescriptor | undefined; | ||
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| beforeEach(() => { | ||
| vi.resetModules(); | ||
| navigatorDescriptor = Object.getOwnPropertyDescriptor(globalThis, "navigator"); | ||
| Object.defineProperty(globalThis, "navigator", { | ||
| value: { userAgent: "Cloudflare-Workers" }, | ||
| configurable: true, | ||
| writable: true, | ||
| }); | ||
| }); | ||
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| afterEach(() => { | ||
| vi.unstubAllGlobals(); | ||
| if (navigatorDescriptor) { | ||
| Object.defineProperty(globalThis, "navigator", navigatorDescriptor); | ||
| } else { | ||
| delete (globalThis as any).navigator; | ||
| } | ||
| vi.resetModules(); | ||
| }); | ||
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| const loadAllowsEval = async () => { | ||
| const mod = await import("../../core/util.js"); | ||
| return mod.allowsEval.value; | ||
| }; | ||
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| test("disables fast path after startup", async () => { | ||
| expect(await loadAllowsEval()).toBe(false); | ||
| }); | ||
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| test("caches value instead of re-evaluating", async () => { | ||
| const first = await loadAllowsEval(); | ||
| expect(first).toBe(false); | ||
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| vi.stubGlobal("Function", function ThrowingFunction() { | ||
| throw new Error("Function constructor disabled"); | ||
| }); | ||
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| const second = await loadAllowsEval(); | ||
| expect(second).toBe(first); | ||
| }); | ||
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| test("stays disabled when eval is disabled from start", async () => { | ||
| vi.stubGlobal("Function", function ThrowingFunction() { | ||
| throw new Error("Function constructor disabled"); | ||
| }); | ||
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| vi.resetModules(); | ||
| expect(await loadAllowsEval()).toBe(false); | ||
| }); | ||
| }); | ||
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| describe("non-Cloudflare allowsEval behavior", () => { | ||
| beforeEach(() => { | ||
| vi.resetModules(); | ||
| }); | ||
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| afterEach(() => { | ||
| vi.unstubAllGlobals(); | ||
| vi.resetModules(); | ||
| }); | ||
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| const loadAllowsEval = async () => { | ||
| const mod = await import("../../core/util.js"); | ||
| return mod.allowsEval.value; | ||
| }; | ||
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| test("falls back when eval is disabled", async () => { | ||
| vi.stubGlobal("Function", function ThrowingFunction() { | ||
| throw new Error("Function constructor disabled"); | ||
| }); | ||
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| vi.resetModules(); | ||
| expect(await loadAllowsEval()).toBe(false); | ||
| }); | ||
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| test("caches value", async () => { | ||
| const first = await loadAllowsEval(); | ||
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| vi.stubGlobal("Function", function ThrowingFunction() { | ||
| throw new Error("Function constructor disabled"); | ||
| }); | ||
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| const second = await loadAllowsEval(); | ||
| expect(second).toBe(first); | ||
| }); | ||
| }); |
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It's problematic that this is eagerly attempted. It'll throw a warning/error in various environments. Zod currently avoids ever using the function constructor if
z.config({ jitless: true })has been set to avoid spamming users with warnings in these environments. You can still attempt this during module initialization but only when you have high confidence (based onnavigatorthat the code is executing in Cloudflare.Though more broadly—as I understand it
new Function()is only allowed during module initialization, so this doesn't actually help. Zod usesnew Function()insidegetFastPasswhen an object schema is parsing for the first tiem. At that point we're out of module initialization so Zod won't be able to properly JIT] this anyway. Your benchmark should include an object parse operation - it would reveal this.Thinking about this more—there's no guarantee that a Zod schema is defined top-level either so getting Zod JIT to work is just not really possible in the general case until
new Functioncan be enabled throughout execution.Let me know if I'm missing something. Maybe anonrig has thoughts.
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thanks, will take that on and have a think :)
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ahhh this is rough. thanks, explains Sunil's comment.
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closing this :)