When a file handle is needed and the last event in the queue is also
a get_file_handle event with the same arguments, instead of queueing
a new event, just remember to cache/re-use the resulting handle from
the previous event. This depends on get_file_handle handlers not
changing global state that is also used to derive the file handle
string.
Versus from synchronous function calls, which doesn't work well because
the function call can see a script-layer state that doesn't reflect
the state as it will be in terms of the event/network stream.
