CountOpenFiles returns how many entries are currently in the table in a threadsafe manner.

Register creates an open file table entry for "qi" (or incrementes the reference count if the entry already exists) and returns the entry.

Unregister decrements the reference count for "qi" and deletes the entry from the open file table if the reference count reaches 0.

WriteOpCount returns the write lock counter value.

Entry is an entry in the open file table.