ISM force_merge explanation

Have a question related to action force_merge the official doc says that " This operation attempts to set the index to a read-only state before starting the merging process."
What happens with the state of the index after the force_merge action is completed, does it stay in read_only???

It should not remain read only after a force merge completes. It attempts to go read only to ensure that there is no data loss during the merge operation. After it completes the index should resume normal operations.