javascript / expert
Snippet
Asynchronous Mutex for Exclusive Resource Access
A Mutex ensures that only one asynchronous operation can access a critical section at a time. It chains promises to create a queue where each operation waits for the previous one to resolve, preventing race conditions in shared environments like server-side caches.
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class Mutex {#promise = Promise.resolve();async acquire() {let release;const next = new Promise(res => release = res);const current = this.#promise;this.#promise = current.then(() => next);await current;return release;}}// Usage in Next.js Route Handlerconst mutex = new Mutex();export async function POST() {const release = await mutex.acquire();try {// Critical section} finally {release();}}
nextjs
Breakdown
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this.#promise = current.then(() => next);
Appends the new lock request to the existing chain of promises.
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await current;
Waits for all previously queued operations to finish before proceeding.
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return release;
Returns a function that resolves the 'next' promise, allowing the next queued task to run.