presto-main/src/main/java/io/prestosql/operator/WorkProcessorUtils.java/WorkProcessorUtils/getBlockedFuture
class WorkProcessorUtils:        @Override
        public ListenableFuture<?> getBlockedFuture()
        {
            checkState(state != null && state.getType() == ProcessState.Type.BLOCKED, "Must be blocked to get blocked future");
            return state.getBlocked();
        }