void removeTranxnMappingsAndRollbackExpiredTransaction(List tranxns) {
    Object[] threads = transactionMap.keySet().toArray();
    int len = threads.length;
    Object tx = null;
    boolean removed = false;
    Object temp = null;
    for (final Object thread : threads) {
      tx = transactionMap.get((temp = thread));
      removed = tranxns.remove(tx);
      if (removed) {
        transactionMap.remove(temp);
        GlobalTransaction globalTransaction = (GlobalTransaction) globalTransactionMap.remove(tx);
        try {
          globalTransaction.rollback();
        } catch (Exception ignore) {
        }
      }
    }
  }
Get the Global Transaction associated with the calling thread
geode-core/src/main/java/org/apache/geode/internal/jta/TransactionManagerImpl.java