Function ReadModifyUpdate

coderd/database/tx.go:32–49

ReadModifyUpdate is a helper function to run a db transaction that reads some object(s), modifies some of the data, and writes the modified object(s) back to the database. It is run in a transaction at RepeatableRead isolation so that if another database client also modifies the data we are writing

(db Store, f func(tx Store) error,
)

// transaction fails, but here we retry.  The second attempt we read A=2, B=1,
// then write A=2, B=2 as desired, and this succeeds.
func ReadModifyUpdate(db Store, f func(tx Store) error,
) error {
	var err error
	for retries := 0; retries < maxRetries; retries++ {
		err = db.InTx(f, &TxOptions{
			Isolation: sql.LevelRepeatableRead,
		})
		var pqe *pq.Error
		if xerrors.As(err, &pqe) {
			if pqe.Code == "40001" {
				// serialization error, retry
				continue
			}
		}
		return err
	}
	return xerrors.Errorf("too many errors; last error: %w", err)
}