presto-main/src/main/java/io/prestosql/transaction/InMemoryTransactionManager.java/InMemoryTransactionManager/abortInternal
class InMemoryTransactionManager:        private synchronized ListenableFuture<?> abortInternal()
        {
            // the callbacks in statement performed on another thread so are safe
            return nonCancellationPropagating(Futures.allAsList(connectorIdToMetadata.values().stream()
                    .map(connection -> finishingExecutor.submit(() -> safeAbort(connection)))
                    .collect(toList())));
        }