lib/cache/multi.ts

// Copyright (c) 2018, Compiler Explorer Authors
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import {GetResult} from '../../types/cache.interfaces';

import {BaseCache} from './base';

// A write-through multiple cache.
// Writes get pushed to all caches, but reads are serviced from the first cache that returns
// a hit.
export class MultiCache extends BaseCache {
    private readonly upstream: BaseCache[];

    constructor(cacheName, ...upstream) {
        super(cacheName, 'Multi', 'multi');
        this.countersEnabled = false;
        this.upstream = upstream;
    }

    override statString(): string {
        return `${super.statString()}. ${this.upstream.map(c => `${c.details}: ${c.statString()}`).join('. ')}`;
    }

    private async propagateHitToMissedCaches(caches: BaseCache[], key: string, data: Buffer): Promise<void> {
        await Promise.all(caches.map(c => c.put(key, data)));
    }

    override async getInternal(key: string): Promise<GetResult> {
        const misses: BaseCache[] = [];

        for (const cache of this.upstream) {
            const result = await cache.get(key);

            if (result.hit) {
                await this.propagateHitToMissedCaches(misses, key, result.data);
                return result;
            }

            // keep track of caches that missed so we can write to them if we do hit
            misses.push(cache);
        }

        // all caches missed
        return {hit: false};
    }

    async putInternal(object: string, value: Buffer, creator?: string): Promise<void> {
        await Promise.all(this.upstream.map(cache => cache.put(object, value, creator)));
    }
}