Executor: OSError: [Errno 24] Too many open files

Not sure what happened but yesterday, my gateway refused serving new requests and the executor logs were filled with the error OSError: [Errno 24] Too many open files.

There were a couple of defunct executor PIDs, so I restarted the service and it seemed to have fixed itself.

Not sure what happened there, but it would be good to look into what could have been leaking these fds.