Is it safe to call OPENSSL_thread_stop multiple times?

[jay]

A libcurl dll built with statically linked OpenSSL may cause a memory leak because OPENSSL_thread_stop is not called. We could call OPENSSL_thread_stop in our DllMain on DLL_THREAD_DETACH, however if OpenSSL is a DLL then it also calls that function in its DllMain on DLL_THREAD_DETACH. Is it allowed to call the function twice?

I do not see it documented and I can't tell from the source. It looks like the function tries to retrieve a tls local value and passes it on to init_thread_remove_handlers even if that value is NULL.

[mattcaswell]

Yes, I believe this should be fine.

OPENSSL_thread_stop calls init_get_thread_local to obtain the THREAD_EVENT_HANDLER list. On a second call of OPENSSL_thread_stop this return value should be NULL.

It then calls init_thread_stop with that value - which just immediately returns if the handler list is NULL, and init_thread_remove_handlers which is a no-op if the handler list is NULL.

Finally it calls OPENSSL_free with the NULL pointer - which is also fine and a no-op.

[jay]

Thanks. curl/curl#12408