pg-transactional-outbox/src/replication/concurrency-controller/create-semaphore-concurrency-controller.ts

A PostgreSQL based transactional outbox and inbox pattern implementation to support exactly once message processing (with at least once message delivery).

import { Semaphore } from 'async-mutex';
import { ReplicationConcurrencyController } from './concurrency-controller';

/**
 * Uses a semaphore to execute up to a given amount of messages in parallel. Any
 * additional message waits until a currently processed message finishes.
 * @returns The controller to acquire and release the semaphore and to cancel all semaphores
 */
export const createReplicationSemaphoreConcurrencyController = (
  maxParallel: number,
): ReplicationConcurrencyController => {
  const semaphore = new Semaphore(maxParallel);
  return {
    acquire: async () => {
      // eslint-disable-next-line @typescript-eslint/no-unused-vars
      const [_, release] = await semaphore.acquire();
      return release;
    },
    cancel: semaphore.cancel.bind(semaphore),
  };
};