[EXTERNAL] Re: Calling OpenSSL_thread_stop() multiple times

[Matt Caswell]

On 24/08/2023 09:28, Martin Bonner wrote:
> Yes, I read all that documentation.  I didn't interpret that as saying:
> "It is safe to call this OPENSSL_thread_stop(_ex) from DLLMain in
> response to DLL_THREAD_DETACH".
> 
> I think I was confused by the wording:
> "in response to a DLL_THREAD_DETACH message being sent to the
> libcrypto32.dll entry point"
> 
> Firstly, I thought the word "message" meant a WM_MESSAGE, and secondly,
> I didn't realize "libcrypto32.dll entry point" meant "DLLMain".
> 
> I think that quoted text would be better written as:
> "in response to the DLLMain for libcrypto32.dll being called with
> dwReason==DLL_THREAD_DETACH"
> 
> This does raise the question: if libcrypto is automatically calling
> OPENSSL_thread_stop(), why does Deepak B need to do so (but that is
> curiosity, not safety)?

This doesn't happen automatically if you link OpenSSL statically (on 
Windows). So if you link your *own* dll to OpenSSL statically then you 
might need to use this approach.

Matt


> 
> Finally:
>> OPENSSL_thread_stop() is used for freeing resources and I wouldn't
>> generally expect more complex processing to occur in it.
> 
> I wouldn't expect complex processing, but if some provider kept a
> count of threads using an auxiliary DLL, and did a FreeLibrary in
> OPENSSL_thread_stop if that call falls to zero, that would not be
> good.
> 
> 
> 
> Martin Bonner
> 
> 
> On 24/08/2023 08:38, Martin Bonner via openssl-users wrote:
> 
> OPENSSL_thread_stop() is used for freeing resources and I wouldn't
> generally expect more complex processing to occur in it.
> 
> If running on Windows and linking to OpenSSL dynamically then
> OPENSSL_thread_stop() is automatically called (the application does not
> need to do anything special). OpenSSL itself does this from DllMain and
> using DLL_THREAD_DETACH:
> 
> https://github.com/openssl/openssl/blob/84a149254f977f502dd2314169812fc6eae8c309/crypto/dllmain.c*L28-L44
> 
> The documentation for OPENSSL_thread_stop() does explicitly mention this:
> 
> "Resources local to a thread are deallocated automatically when the
> thread exits (e.g. in a pthreads environment, when pthread_exit() is
> called). On Windows platforms this is done in response to a
> DLL_THREAD_DETACH message being sent to the libcrypto32.dll entry point.
> Some windows functions may cause threads to exit without sending this
> message (for example ExitProcess()). If the application uses such
> functions, then the application must free up OpenSSL resources directly
> via a call to OPENSSL_thread_stop() on each thread. Similarly this
> message will also not be sent if OpenSSL is linked statically, and
> therefore applications using static linking should also call
> OPENSSL_thread_stop() on each thread. Additionally if OpenSSL is loaded
> dynamically via LoadLibrary() and the threads are not destroyed until
> after FreeLibrary() is called then each thread should call
> OPENSSL_thread_stop() prior to the FreeLibrary() call."
> 
> 
> 
> Matt
> 
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