nuxt-app/server/scheduler/executor-pool.ts

import log4js from "logger";

const logger = log4js.getLogger("SCHEDULER");

type QueuedTask = {
  run: () => void;
};

export class ExecutorPool {
  private running = 0;
  private queue: QueuedTask[] = [];
  private maxConcurrency: number;

  constructor(maxConcurrency = 5) {
    this.maxConcurrency = maxConcurrency;
  }

  get activeCount(): number {
    return this.running;
  }

  get queuedCount(): number {
    return this.queue.length;
  }

  async execute(fn: () => Promise<void>): Promise<void> {
    if (this.running >= this.maxConcurrency) {
      logger.info(
        "Pool full (%d/%d), queuing task (%d in queue)",
        this.running,
        this.maxConcurrency,
        this.queue.length + 1
      );
      await new Promise<void>((resolve) => {
        this.queue.push({ run: resolve });
      });
    }

    this.running++;
    try {
      await fn();
    } finally {
      this.running--;
      const next = this.queue.shift();
      if (next) {
        next.run();
      }
    }
  }
}