Questions about multi-threading

[haypo at inl.fr]

Hi,

I'm working on the firewall NuFW [1]. I used gprof to find functions which
takes a lot of time. I'm not sure, but I think that gcrypt really uses too
much mutexes lock() and unlock(). I read gcrypt source code, and used gdb
on server to catch lock() calls.

I didn't understood everything, but I have some questions.

(a) Why do ath_mutex_lock() and ath_mutex_unlock() call mutex_init()? It
looks very weird for me, since this function use another mutex!

(b) Why do ath_mutex_destroy() call mutex_init()??? It's stupid to create
a mutex if it doesn't exist ... to destroy it just after its creation!?

(c) Can a mutex lock() or unlock() fails? (or: it is necessary to check
error code?)

(d) Would it be possible to make random() functions (eg.
gcry_random_bytes() and gcry_create_nonce()) really thread safe? (can be
called in two different threads at the same time and not block one the
call until the first ends)

(e) Why using REGISTER_(...); macro and not simply call them in a function
like "gcrypt_global_init();"? Eg. "REGISTER_DEFAULT_DIGESTS" in
cipher/md.c, it uses a mutex to check if digests are already registred or
not. "REGISTER_DEFAULT_DIGESTS" is called in 7 different functions, but is
it really needed?

[1] Firewall NuFW
    http://www.nufw.org/

Victor Stinner