key_is_using_space t key returns
key is using some space in
key_is_using_space t key, but it is also possible that that
key_is_using_space t key && not (mem t key).
reclaim_space_for_keys_with_unused_data t reclaims space for all keys in
data has been detected (by a finalizer) to be unused. Only
keys such that
key_is_using_space t key && not (mem t key) will be reclaimed.
set_run_when_unused_data t ~thread_safe_f calls
thread_safe_f in the finalizer
attached to each
t, after ensuring the entry being finalized will be
handled in the next call to
reclaim_space_for_keys_with_unused_data. This can be
used to arrange to call
reclaim_space_for_keys_with_unused_data at a convenient time
in the future.
thread_safe_f must be thread safe -- it is *not* safe for it to call