[Click] Locking and concurrency management in Click

[Yogesh Mundada]

Hi,

I see that there are three types of locks provides in sync.hh. All of
them are polling locks. If I try to declare a semaphore mutex using
DECLARE_MUTEX, I get compile time errors. A quick grep through the
source code for mutex, does not show any element using it.

sync.hh mentions that "Therefore, Spinlock should not be used to, for
example, synchronize handlers with main element threads." In that case
what locking mechanism is used to synchronize handlers and main
element threads?
If I want to use kernel-user space communication mechanism like
netlink/generic netlink in my element, what is the suggested way to
synchronize the access?

-Yogesh