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From Darryl Miles <>
Subject Re: Creating a thread safe module and the problem of calling of 'CRYPTO_set_locking_callback' twice!
Date Wed, 06 Dec 2006 18:20:55 GMT
Joe Orton wrote:
> What I do with OpenSSL in neon is to check that the existing callback is 
> NULL before registering a new callback; and likewise to check that the 
> ID callback is the one neon previously registered before un-registering 
> it later.  If everybody did that it would be relatively safe.

Is there an API to get the current value ?

It shouldn't be too hard to attach a piece of memory to a keyed 
namespace which the core module maintains.  3 primitives should do the 
trick.  data = get(key), set(key, data), set_if_null(key, data) where 
the set_if_null() operation is especially thread-safe.

This would be little impact/bloat on core module, but be user extendable 
to allow other such things.  Someone just needs to maintain an assigned 
key value list.

A notice board for modules to talk to each other.

> The OpenSSL guys have actually obviated the ID callback for some future 
> release, it was entirely unportable because of the cast-to-long issue 
> anyway; but the locking callback remains.

(void *) in the latest releases AFAIK.  This is to address this very 


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