Update multi-thread FAQ

* Is OpenSSL thread-safe?

Yes (with limitations: an SSL connection may not concurrently be used

by multiple threads).  On Windows and many Unix systems, OpenSSL

automatically uses the multi-threaded versions of the standard

libraries.  If your platform is not one of these, consult the INSTALL

file.

Multi-threaded applications must provide two callback functions to

OpenSSL by calling CRYPTO_set_locking_callback() and

CRYPTO_set_id_callback(), for all versions of OpenSSL up to and

including 0.9.8[abc...]. As of version 1.0.0, CRYPTO_set_id_callback()

and associated APIs are deprecated by CRYPTO_THREADID_set_callback()

and friends. This is described in the threads(3) manpage.

Provided an application sets up the thread callback functions, the

answer is yes. There are limitations; for example, an SSL connection

cannot be used concurrently by multiple threads.  This is true for

most OpenSSL objects.

To do this, your application must call CRYPTO_set_locking_callback()

and one of the CRYPTO_THREADID_set...() API's.  See the OpenSSL threads

manpage for details and "note on multi-threading" in the INSTALL file in

the source distribution.

* I've compiled a program under Windows and it crashes: why?