worker fixes (#4059)

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showing the before and after of your change.

### Change type

- [x] `bugfix`
- [ ] `improvement`
- [ ] `feature`
- [ ] `api`
- [ ] `other`

### Test plan

1. Create a shape...
2.

- [ ] Unit tests
- [ ] End to end tests

### Release notes

- Fixed a bug with...

---------

Co-authored-by: alex <alex@dytry.ch>

scripts/workers/dev.ts

@@ -1,11 +1,20 @@
 import { ChildProcessWithoutNullStreams, spawn } from 'child_process'
 import kleur from 'kleur'
+import { lock } from 'proper-lockfile'
 import stripAnsi from 'strip-ansi'
 
-// at the time of writing, workerd will regularly crash with a segfault
-// but the error is not caught by the process, so it will just hang
-// this script wraps the process, tailing the logs and restarting the process
-// if we encounter the string 'Segmentation fault'
+const lockfileName = __dirname
+
+/**
+ * a long time ago, workerd would regularly crash with a segfault but the error is not caught by the
+ * process, so it will just hang. this script wraps the process, tailing the logs and restarting the
+ * process if we encounter the string 'Segmentation fault'. we think this error is probably fixed
+ * now.
+ *
+ * there's a separate issue where spawning multiple workerd instances at once would cause them to
+ * fight and crash. we use a lockfile to start our wrokerd instances one at a time, waiting for the
+ * previous one to be ready before we start the next.
+ */
 class MiniflareMonitor {
 	private process: ChildProcessWithoutNullStreams | null = null
 
@@ -14,9 +23,10 @@ class MiniflareMonitor {
 		private args: string[] = []
 	) {}
 
-	public start(): void {
-		this.stop() // Ensure any existing process is stopped
-		console.log(`Starting wrangler...`)
+	public async start(): Promise<void> {
+		await this.stop() // Ensure any existing process is stopped
+		await this.lock()
+		await console.log(`Starting wrangler...`)
 		this.process = spawn(this.command, this.args, {
 			env: {
 				NODE_ENV: 'development',
@@ -35,6 +45,11 @@ class MiniflareMonitor {
 
 	private handleOutput(output: string, err = false): void {
 		if (!output) return
+
+		if (output.includes('Ready on') && this.isLocked()) {
+			this.release()
+		}
+
 		if (output.includes('Segmentation fault')) {
 			console.error('Segmentation fault detected. Restarting Miniflare...')
 			this.restart()
@@ -43,18 +58,45 @@ class MiniflareMonitor {
 		}
 	}
 
-	private restart(): void {
+	private async restart(): Promise<void> {
 		console.log('Restarting wrangler...')
-		this.stop()
+		await this.stop()
 		setTimeout(() => this.start(), 3000) // Restart after a short delay
 	}
 
-	private stop(): void {
+	private async stop(): Promise<void> {
+		if (this.isLocked()) await this.release()
 		if (this.process) {
 			this.process.kill()
 			this.process = null
 		}
 	}
+
+	private _lockPromise?: Promise<() => Promise<void>>
+	private isLocked() {
+		return !!this._lockPromise
+	}
+	private async lock() {
+		if (this.isLocked()) throw new Error('Already locked')
+		console.log('Locking...')
+		this._lockPromise = lock(lockfileName, {
+			retries: {
+				minTimeout: 500,
+				retries: 10,
+			},
+		})
+		await this._lockPromise
+		console.log('Locked')
+	}
+	private async release() {
+		if (!this.isLocked()) throw new Error('Not locked')
+		console.log('Releasing...')
+		const lockPromise = this._lockPromise!
+		this._lockPromise = undefined
+		const release = await lockPromise
+		await release()
+		console.log('Released')
+	}
 }
 
 class SizeReporter {
@@ -119,6 +161,7 @@ new MiniflareMonitor('wrangler', [
 	'info',
 	'--var',
 	'IS_LOCAL:true',
+	...process.argv.slice(2),
 ]).start()
 
 new SizeReporter().start()