fix(cache): refcount produce tracking so deletes are not lost (#2272)

fluxer_api/pkgs/cache/src/__tests__/CacheInvalidationRace.test.ts

@@ -3,6 +3,8 @@
 import {InMemoryProvider} from '@pkgs/cache/src/providers/InMemoryProvider';
 import {describe, expect, it} from 'vitest';
 
+const INFLIGHT_OVERFLOW_ENTRIES = 10000;
+
 function deferred<T>(): {promise: Promise<T>; resolve: (value: T) => void; reject: (error: Error) => void} {
 	let resolve!: (value: T) => void;
 	let reject!: (error: Error) => void;
@@ -17,6 +19,10 @@ function flush(): Promise<void> {
 	return new Promise((resolve) => setTimeout(resolve, 0));
 }
 
+function trackedProduceKeys(cache: InMemoryProvider): Array<string> {
+	return [...(cache as unknown as {produceInvalidations: Map<string, unknown>}).produceInvalidations.keys()];
+}
+
 describe('cache invalidation during an in-flight produce', () => {
 	it('does not resurrect a value deleted while the factory was running', async () => {
 		const cache = new InMemoryProvider();
@@ -77,6 +83,73 @@ describe('cache invalidation during an in-flight produce', () => {
 		expect(await cache.get('session')).toBe('retried-session');
 	});
 
+	it('does not resurrect a value deleted after a concurrent caller released its produce', async () => {
+		const cache = new InMemoryProvider();
+		const gate = deferred<string>();
+		const pending = cache.getOrSet('session', async () => await gate.promise, 30);
+		await flush();
+		await cache.set('session', 'served-from-cache', 30);
+		await expect(cache.getOrSet('session', async () => 'unused', 30)).resolves.toBe('served-from-cache');
+		await cache.delete('session');
+		gate.resolve('stale-produce');
+		await expect(pending).resolves.toBe('stale-produce');
+		expect(await cache.get('session')).toBeNull();
+	});
+
+	it('does not resurrect a value deleted while a second overflow produce was running', async () => {
+		const cache = new InMemoryProvider();
+		const fillers: Array<ReturnType<typeof deferred<string>>> = [];
+		const filling: Array<Promise<string>> = [];
+		for (let index = 0; index < INFLIGHT_OVERFLOW_ENTRIES; index++) {
+			const gate = deferred<string>();
+			fillers.push(gate);
+			filling.push(cache.getOrSet(`filler:${index}`, async () => await gate.promise, 30));
+		}
+		await flush();
+		const first = deferred<string>();
+		const second = deferred<string>();
+		const firstProduce = cache.getOrSet('session', async () => await first.promise, 30);
+		const secondProduce = cache.getOrSet('session', async () => await second.promise, 30);
+		await flush();
+		first.resolve('first-produce');
+		await expect(firstProduce).resolves.toBe('first-produce');
+		await cache.delete('session');
+		second.resolve('second-produce');
+		await expect(secondProduce).resolves.toBe('second-produce');
+		expect(await cache.get('session')).toBeNull();
+		for (const gate of fillers) {
+			gate.resolve('filler');
+		}
+		await Promise.all(filling);
+	});
+
+	it('drops produce tracking once the last produce for a key settles', async () => {
+		const cache = new InMemoryProvider();
+		for (let index = 0; index < 50; index++) {
+			const gate = deferred<string>();
+			const pending = cache.getOrSet(`session:${index}`, async () => await gate.promise, 30);
+			await cache.delete(`session:${index}`);
+			gate.resolve('value');
+			await pending;
+		}
+		const shared = deferred<string>();
+		const producer = cache.getOrSet('shared', async () => await shared.promise, 30);
+		const joiner = cache.getOrSet('shared', async () => 'unused', 30);
+		await flush();
+		await cache.delete('shared');
+		shared.resolve('shared-value');
+		await Promise.all([producer, joiner]);
+		const failing = cache.getOrSet(
+			'failing',
+			async () => {
+				throw new Error('produce failed');
+			},
+			30,
+		);
+		await expect(failing).rejects.toThrow('produce failed');
+		expect(trackedProduceKeys(cache)).toEqual([]);
+	});
+
 	it('keeps a later produce cacheable after an earlier one was invalidated', async () => {
 		const cache = new InMemoryProvider();
 		const first = deferred<string>();