// Called when done with the item returned by get_.
// Ignore if item was 0.
void unlock();
-// delete oldest member, returns 1 if item deleted or 0 if none found
+// Delete oldest item.
+// Return number of bytes freed if successful. Return 0 if nothing to delete.
int delete_oldest();
// Calculate current size of cache in bytes
int64_t get_memory_usage();