class TransactionsPool {

    public boolean addTransaction(String transactionHash) {
        Util.check(transactionHash != null, "transaction != null");

        synchronized (locker) {
            if (!checkExistsNoLock(transactionHash)) {
                transactions.add(transactionHash);

                logger.trace("Added {}", transactionHash);

                return (true);
            } else {
                logger.debug("Transaction {} already in pool/processed!", transactionHash);
                return (false);
            }

        }
    }

}