[wrangler] serialize custom build watch events to avoid concurrent runs by dhruv7539 · Pull Request #12704 · cloudflare/workers-sdk

dhruv7539 · 2026-02-27T18:45:07Z

Summary

serialize custom build watch-triggered runs in BundlerController
keep only the latest pending file-change build request when many events arrive in a burst
preserve stale-build suppression by retaining the existing abort-controller checks

Why

Fixes the behavior in #10944 where rapid multi-file changes can start multiple custom builds at once.

Testing

pnpm -C packages/wrangler test src/__tests__/api/startDevWorker/BundleController.test.ts
pnpm -C packages/wrangler exec eslint src/api/startDevWorker/BundlerController.ts src/__tests__/api/startDevWorker/BundleController.test.ts

Added regression test

custom build watcher changes are processed without concurrent custom builds
uses a lock file in a test custom-build script to fail if two builds overlap
updates multiple watched files in quick succession and verifies no Custom build failed events are emitted

changeset-bot · 2026-02-27T18:45:12Z

🦋 Changeset detected

Latest commit: 9e7dab9

The changes in this PR will be included in the next version bump.

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dhruv7539 · 2026-02-27T19:30:30Z

Addressed both actionable comments in the latest push (8ae0df1):\n- fixed wiring in custom-build path to use \n- added a Wrangler patch changeset ()

dhruv7539 · 2026-02-27T19:30:38Z

Addressed both actionable comments in the latest push (8ae0df1ef):

fixed jsxFragment wiring in BundlerController custom-build path to use config.build.jsxFragment
added a Wrangler patch changeset (.changeset/quick-keys-smell.md)

workers-devprod · 2026-04-15T06:28:47Z

Codeowners approval required for this PR:

@cloudflare/wrangler

Show detailed file reviewers

packages/wrangler/src/tests/api/startDevWorker/BundleController.test.ts: [@cloudflare/wrangler]
packages/wrangler/src/api/startDevWorker/BundlerController.ts: [@cloudflare/wrangler]

devin-ai-integration

Devin Review found 1 new potential issue.

View 7 additional findings in Devin Review.

devin-ai-integration · 2026-04-15T06:35:28Z

 			);
 		});
+
+		test("custom build watcher changes are processed without concurrent custom builds", async () => {


🟡 New test uses global expect instead of test context ({ expect }), violating AGENTS.md rule

The new test at line 258 uses async () => { without destructuring expect from the test context, then calls expect(customBuildErrors).toHaveLength(0) at line 313 using the global expect. This violates the explicit rule in packages/wrangler/AGENTS.md: "Never import expect from vitest — use test context ({ expect }) => {}". Every other test in this file (lines 72, 132, 185, 318, 371, 493, 603, 644) correctly uses the async ({ expect }) => { pattern.

Suggested change

test("custom build watcher changes are processed without concurrent custom builds", async () => {

test("custom build watcher changes are processed without concurrent custom builds", async ({ expect }) => {

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pkg-pr-new · 2026-04-15T08:26:10Z

create-cloudflare

npm i https://pkg.pr.new/create-cloudflare@12704

@cloudflare/kv-asset-handler

npm i https://pkg.pr.new/@cloudflare/kv-asset-handler@12704

miniflare

npm i https://pkg.pr.new/miniflare@12704

@cloudflare/pages-shared

npm i https://pkg.pr.new/@cloudflare/pages-shared@12704

@cloudflare/unenv-preset

npm i https://pkg.pr.new/@cloudflare/unenv-preset@12704

@cloudflare/vite-plugin

npm i https://pkg.pr.new/@cloudflare/vite-plugin@12704

@cloudflare/vitest-pool-workers

npm i https://pkg.pr.new/@cloudflare/vitest-pool-workers@12704

@cloudflare/workers-editor-shared

npm i https://pkg.pr.new/@cloudflare/workers-editor-shared@12704

wrangler

npm i https://pkg.pr.new/wrangler@12704

commit: c5495bd

workers-devprod · 2026-04-20T09:17:16Z

Codeowners approval required for this PR:

@cloudflare/wrangler

Show detailed file reviewers

packages/wrangler/src/tests/api/startDevWorker/BundleController.test.ts: [@cloudflare/wrangler]
packages/wrangler/src/api/startDevWorker/BundlerController.ts: [@cloudflare/wrangler]

devin-ai-integration

Devin Review found 1 new potential issue.

View 10 additional findings in Devin Review.

devin-ai-integration · 2026-04-20T09:25:13Z

+			while (this.#pendingCustomBuild) {
+				const nextBuild = this.#pendingCustomBuild;
+				this.#pendingCustomBuild = undefined;
+				await this.#runCustomBuild(
+					nextBuild.config,
+					nextBuild.filePath,
+					nextBuild.buildAborter
+				);


🟡 Stale pending custom build executes its external command when aborter is already aborted

When a config update (#startCustomBuild) occurs while a custom build is pending in the queue, #startCustomBuild at BundlerController.ts:230 aborts this.#customBuildAborter (which is the same AbortController stored in #pendingCustomBuild.buildAborter). However, #runPendingCustomBuilds at line 67-74 does not check buildAborter.signal.aborted before dequeuing and running the stale pending build, and #runCustomBuild at line 88-89 emits a bundleStart event and executes the external build command before checking the abort signal at line 101. This means a build known to be cancelled still runs its external command, emits a spurious bundleStart (without a matching bundleComplete), and if the external command fails, emits a confusing error event to downstream consumers (ProxyController, RuntimeControllers per DevEnv.ts:101-104). Adding an early abort guard would avoid this unnecessary work.

Suggested change

while (this.#pendingCustomBuild) {

const nextBuild = this.#pendingCustomBuild;

this.#pendingCustomBuild = undefined;

await this.#runCustomBuild(

nextBuild.config,

nextBuild.filePath,

nextBuild.buildAborter

);

while (this.#pendingCustomBuild) {

const nextBuild = this.#pendingCustomBuild;

this.#pendingCustomBuild = undefined;

if (nextBuild.buildAborter.signal.aborted) {

continue;

}

await this.#runCustomBuild(

nextBuild.config,

nextBuild.filePath,

nextBuild.buildAborter

);

}

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petebacondarwin · 2026-04-25T13:09:11Z

There are outstanding review comments from Devin to address. Marking as draft while these are resolved.

petebacondarwin · 2026-04-28T12:54:36Z

Hi @dhruv7539 — we're doing some cleanup of stale draft PRs.

This PR has been quiet since 2026-04-25. Could you let us know within 14 days whether you're still planning to continue?

If yes: please leave a comment with a status update or push a rebase, and we'll keep it open.
If no: no need to reply — we'll close it after 14 days, and you can always reopen later if you pick it back up.

Thanks!

petebacondarwin · 2026-07-30T15:34:54Z

Thanks for this @dhruv7539, and sorry it sat for so long. The code this touches was rewritten by #14462 and #14561 in the meantime, so rather than ask you to untangle the conflicts I've re-implemented your fix on top of current main in #14936, with you as co-author.

Your approach (serialize the watcher-triggered builds, keep only the latest pending request) is what landed there. On top of it: the watcher events are now debounced so a burst collapses to a single build, and the regression test needed a liveness-aware lock file — since #14462 a superseded build is killed and leaves its lock behind, which would have made the original test's existsSync check fail spuriously.

Closing this as superseded by #14936. Thanks again for the fix and for the report triage on #10944.

dhruv7539 requested a review from a team as a code owner February 27, 2026 18:45

dhruv7539 mentioned this pull request Feb 27, 2026

Prevent custom builds from executing concurrenctly #10944

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petebacondarwin force-pushed the codex/serialize-custom-build-watch-events-10944 branch from 8ae0df1 to 90cb61d Compare April 15, 2026 06:28

petebacondarwin requested a review from workers-devprod as a code owner April 15, 2026 06:28

devin-ai-integration Bot reviewed Apr 15, 2026

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petebacondarwin requested review from a team and vicb and removed request for a team April 15, 2026 06:53

dhruv7539 added 2 commits April 15, 2026 09:18

Serialize custom build watcher events in dev

f4d8c62

Fix jsxFragment config in custom dev bundling

c5495bd

petebacondarwin force-pushed the codex/serialize-custom-build-watch-events-10944 branch from 90cb61d to c5495bd Compare April 15, 2026 08:18

workers-devprod added this to workers-sdk Apr 15, 2026

github-project-automation Bot moved this to Untriaged in workers-sdk Apr 15, 2026

Merge branch 'main' into codex/serialize-custom-build-watch-events-10944

9e7dab9

devin-ai-integration Bot reviewed Apr 20, 2026

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petebacondarwin marked this pull request as draft April 25, 2026 13:09

petebacondarwin closed this Jun 29, 2026

github-project-automation Bot moved this from Untriaged to Done in workers-sdk Jun 29, 2026

petebacondarwin reopened this Jun 29, 2026

github-project-automation Bot moved this from Done to Untriaged in workers-sdk Jun 29, 2026

petebacondarwin mentioned this pull request Jun 29, 2026

[wrangler] Abort custom builds on dev teardown #14462

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petebacondarwin mentioned this pull request Jul 30, 2026

[wrangler] Serialize custom build watcher events to avoid concurrent runs #14936

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petebacondarwin closed this Jul 30, 2026

github-project-automation Bot moved this from Untriaged to Done in workers-sdk Jul 30, 2026

	test("custom build watcher changes are processed without concurrent custom builds", async () => {
	test("custom build watcher changes are processed without concurrent custom builds", async ({ expect }) => {

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Added regression test

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