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Implement DebounceLoader

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This commit is contained in:
Hidekazu Kobayashi 2023-10-07 05:52:04 +00:00
parent e695c60a1d
commit 6e46c977e8
2 changed files with 137 additions and 0 deletions
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49
packages/backend/src/misc/loader.ts Normal file
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export type FetchFunction<K, V> = (key: K) => Promise<V>;
type ResolveReject<V> = Parameters<ConstructorParameters<typeof Promise<V>>[0]>;
type ResolverPair<V> = {
resolve: ResolveReject<V>[0];
reject: ResolveReject<V>[1];
};
export class DebounceLoader<K, V> {
private resolverMap = new Map<K, ResolverPair<V>>();
private promiseMap = new Map<K, Promise<V>>();
private resolvedPromise = Promise.resolve();
constructor(private loadFn: FetchFunction<K, V>) {}
public load(key: K): Promise<V> {
const promise = this.promiseMap.get(key);
if (typeof promise !== 'undefined') {
return promise;
}
const isFirst = this.promiseMap.size === 0;
const newPromise = new Promise<V>((resolve, reject) => {
this.resolverMap.set(key, { resolve, reject });
});
this.promiseMap.set(key, newPromise);
if (isFirst) {
this.enqueueDebouncedLoadJob();
}
return newPromise;
}
private runDebouncedLoad(): void {
const resolvers = [...this.resolverMap];
this.resolverMap.clear();
this.promiseMap.clear();
for (const [key, { resolve, reject }] of resolvers) {
this.loadFn(key).then(resolve, reject);
}
}
private enqueueDebouncedLoadJob(): void {
this.resolvedPromise.then(() => {
process.nextTick(() => {
this.runDebouncedLoad();
});
});
}
}

88
packages/backend/test/unit/misc/loader.ts Normal file
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import { DebounceLoader } from '@/misc/loader.js';
class Mock {
loadCountByKey = new Map<number, number>();
load = async (key: number): Promise<number> => {
const count = this.loadCountByKey.get(key);
if (typeof count === 'undefined') {
this.loadCountByKey.set(key, 1);
} else {
this.loadCountByKey.set(key, count + 1);
}
return key * 2;
};
reset() {
this.loadCountByKey.clear();
}
}
describe(DebounceLoader, () => {
describe('single request', () => {
it('loads once', async () => {
const mock = new Mock();
const loader = new DebounceLoader(mock.load);
expect(await loader.load(7)).toBe(14);
expect(mock.loadCountByKey.size).toBe(1);
expect(mock.loadCountByKey.get(7)).toBe(1);
});
});
describe('two duplicated requests at same time', () => {
it('loads once', async () => {
const mock = new Mock();
const loader = new DebounceLoader(mock.load);
const [v1, v2] = await Promise.all([
loader.load(7),
loader.load(7),
]);
expect(v1).toBe(14);
expect(v2).toBe(14);
expect(mock.loadCountByKey.size).toBe(1);
expect(mock.loadCountByKey.get(7)).toBe(1);
});
});
describe('two different requests at same time', () => {
it('loads twice', async () => {
const mock = new Mock();
const loader = new DebounceLoader(mock.load);
const [v1, v2] = await Promise.all([
loader.load(7),
loader.load(13),
]);
expect(v1).toBe(14);
expect(v2).toBe(26);
expect(mock.loadCountByKey.size).toBe(2);
expect(mock.loadCountByKey.get(7)).toBe(1);
expect(mock.loadCountByKey.get(13)).toBe(1);
});
});
describe('non-continuous same two requests', () => {
it('loads twice', async () => {
const mock = new Mock();
const loader = new DebounceLoader(mock.load);
expect(await loader.load(7)).toBe(14);
expect(mock.loadCountByKey.size).toBe(1);
expect(mock.loadCountByKey.get(7)).toBe(1);
mock.reset();
expect(await loader.load(7)).toBe(14);
expect(mock.loadCountByKey.size).toBe(1);
expect(mock.loadCountByKey.get(7)).toBe(1);
});
});
describe('non-continuous different two requests', () => {
it('loads twice', async () => {
const mock = new Mock();
const loader = new DebounceLoader(mock.load);
expect(await loader.load(7)).toBe(14);
expect(mock.loadCountByKey.size).toBe(1);
expect(mock.loadCountByKey.get(7)).toBe(1);
mock.reset();
expect(await loader.load(13)).toBe(26);
expect(mock.loadCountByKey.size).toBe(1);
expect(mock.loadCountByKey.get(13)).toBe(1);
});
});
});