[openssl-dev] [openssl-team] Discussion: design issue: async and -lpthread

[Nico Williams]

On Wed, Dec 09, 2015 at 09:27:16AM +1000, Paul Dale wrote:
> It will be possible to support atomics in such a way that there is no
> performance penalty for machines without them or for single threaded
> operation.  My sketcy design is along the lines of adding a new API
> CRYPTO_add_atomic that takes the same arguments as CRYPTO_add (i.e.
> reference to counter, value to add and lock to use):
> 
> CRYPTO_add_atomic(int *addr, int amount, int lock)
>     if have-atomics then
>         atomic_add(addr, amount)
>     else if (lock == have-lock-already)
>         *addr += amount
>     else
>         CRYPTO_add(addr, amount, lock)

"have-atomics" must be known at compile time.

"lock" should not be needed because we should always have atomics, even
when we don't have true atomics: just use a global lock in a stub
implementation of atomic_add() and such.  KISS.  Besides, this will add
pressure to add true atomics wherever they are truly needed.

Nico
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