lib/cache/multi.js

// Copyright (c) 2018, Compiler Explorer Authors
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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 {
    constructor(cacheName, ...upstream) {
        super(cacheName, 'Multi', 'multi');
        this.countersEnabled = false;
        this.upstream = upstream;
    }

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

    async getInternal(key) {
        for (const cache of this.upstream) {
            const result = await cache.get(key);
            // TODO: could propagate hits to lower-level caches. But that's a lot of work and it's not
            // clear to me it is better than just serving from the lowest-level cache.
            if (result.hit) return result;
        }
        return {hit: false};
    }

    putInternal(object, value, creator) {
        return Promise.all(this.upstream.map(cache => {
            return cache.put(object, value, creator);
        }));
    }
}