Modifies the registration of client using EPOLL_CTL_MOD.
More precisely, the events of the current registration of
client.fileHandle are set to client.events and the registration
attachment is set to client.
If this fails with ENOENT, which means, client.fileHandle turned
out not to be registered, a new registration of the client is created
using EPOLL_CTL_ADD. This fallback is intended only to be used when a
file descriptor is unexpectedly unregistered as it happens when it is
closed.
Modifies the registration of client using EPOLL_CTL_MOD. More precisely, the events of the current registration of client.fileHandle are set to client.events and the registration attachment is set to client.
If this fails with ENOENT, which means, client.fileHandle turned out not to be registered, a new registration of the client is created using EPOLL_CTL_ADD. This fallback is intended only to be used when a file descriptor is unexpectedly unregistered as it happens when it is closed.