lib/cache/multi.js

// Copyright (c) 2018, Compiler Explorer Authors
// All rights reserved.
//
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// modification, are permitted provided that the following conditions are met:
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// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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const BaseCache = require('./base.js');

// A write-through multiple cache.
// Writes get pushed to all caches, but reads are serviced from the first cache that returns
// a hit.
class MultiCache extends BaseCache {
    constructor(...upstream) {
        super("Multi");
        this.upstream = upstream;
    }

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

    getInternal(key) {
        let promiseChain = Promise.resolve({hit: false});
        for (let cache of this.upstream) {
            promiseChain = promiseChain.then(upstream => {
                if (upstream.hit) {
                    // 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.
                    return upstream;
                }
                return cache.get(key);
            });
        }
        return promiseChain;
    }

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

module.exports = MultiCache;