Thread locking callbacks into the interpreter impose considerable overhead.
The standard library's ssl module registers its own thread locking and id
callback functions. Registration of the latter can be detected by a call to
the OpenSSL library. In this case, do not set the Python callback function
and therefore keep using the more efficient ssl module functions.
The new module tlock provides the locking callback function the OpenSSL library
requires for the case where multiple threads enter it concurrently. tlock is
now automatically initialized by sslconnection's module startup code, and does
nothing if the executing Python environment does not provide threading.
Note that this does introduce some overhead. For example, during the transfer
of CERTFILE by test_socketserver, about 300 locking callbacks are received.
Ray Brown