sequelize/lib/dialects/mssql/async-queue.ts

Sequelize is a promise-based Node.js ORM tool for Postgres, MySQL, MariaDB, SQLite, Microsoft SQL Server, Amazon Redshift and Snowflake’s Data Cloud. It features solid transaction support, relations, eager and lazy loading, read replication and more.

import { BaseError, ConnectionError } from '../../errors';

/**
 * Thrown when a connection to a database is closed while an operation is in progress
 */
export class AsyncQueueError extends BaseError {
  constructor(message: string) {
    super(message);
    this.name = 'SequelizeAsyncQueueError';
  }
}

class AsyncQueue {
  previous: Promise<unknown>;
  closed: boolean;
  rejectCurrent: (reason?: any) => void;

  constructor() {
    this.previous = Promise.resolve();
    this.closed = false;
    this.rejectCurrent = () => {
      /** do nothing */
    };
  }

  close() {
    this.closed = true;
    this.rejectCurrent(
      new ConnectionError(
        new AsyncQueueError(
          'the connection was closed before this query could finish executing'
        )
      )
    );
  }

  enqueue(asyncFunction: (...args: any[]) => Promise<unknown>) {
    // This outer promise might seems superflous since down below we return asyncFunction().then(resolve, reject).
    // However, this ensures that this.previous will never be a rejected promise so the queue will
    // always keep going, while still communicating rejection from asyncFunction to the user.
    return new Promise((resolve, reject) => {
      this.previous = this.previous.then(() => {
        this.rejectCurrent = reject;
        if (this.closed) {
          return reject(
            new ConnectionError(
              new AsyncQueueError(
                'the connection was closed before this query could be executed'
              )
            )
          );
        }
        return asyncFunction().then(resolve, reject);
      });
    });
  }
}

export default AsyncQueue;