=head1 HISTORY
-CRYPTO_set_locking_callback() is
-available in all versions of SSLeay and OpenSSL.
-CRYPTO_num_locks() was added in OpenSSL 0.9.4.
-All functions dealing with dynamic locks were added in OpenSSL 0.9.5b-dev.
B<CRYPTO_THREADID> and associated functions were introduced in OpenSSL 1.0.0
to replace (actually, deprecate) the previous CRYPTO_set_id_callback(),
CRYPTO_get_id_callback(), and CRYPTO_thread_id() functions which assumed