How to process parallel balance deduction operations sequentially to avoid double deduction (race condition)?

To avoid race conditions during parallel balance deduction operations, it is necessary to ensure sequential access to the resource. In Node.js, this can be achieved in several ways:

1. Use transactions and locks at the database level (e.g., SELECT ... FOR UPDATE).
2. Implement a task queue that processes deductions sequentially.
3. Use atomic database operations (e.g., increment/decrement operations).

Example using a promise-based queue:

const queue = [];
let processing = false;

function processQueue() {
  if (processing || queue.length === 0) return;
  processing = true;
  const {amount, resolve, reject} = queue.shift();

  // Balance deduction function
  debitBalance(amount).then(resolve).catch(reject).finally(() => {
    processing = false;
    processQueue();
  });
}

function debitBalanceSequential(amount) {
  return new Promise((resolve, reject) => {
    queue.push({amount, resolve, reject});
    processQueue();
  });
}

Thus, the deduction operations will be executed strictly in order, preventing race conditions.