Unusual error creating a SSL context with SSL_CTX_new
openssl 多线程编程中会出现下面的问题：
error:140A90F1:SSL routines:SSL_CTX_new:unable to load ssl2 md5 routines
查找了如下资料：
http://comments.gmane.org/gmane.comp.lib.boost.asio.user/2099
Well I think I have figured out what the issue is, or at least narrowed it down. I have been able to provide a work around for our needs but I wanted to post this in case someone came across this same issue. It appears to be an issue with some type of static member initialization inside the openssl library. I have 2 libraries, both of them use the openssl library, let's call them A and B. When the application starts up both A & B are able to successfully create a security context. Later, when library B tries to create another security context it fails. Both library A and B are module plugins to our application so they both will load but if one is not needed it is unloaded. So once I realized that, I ran some experiments. If just A is loaded then things work fine. If just B is loaded then things work fine. If A and B are loaded, then A is unloaded, B fails If A and B are loaded, then B is unloaded, A fails If A is loaded, then unloaded, then B is loaded, B works fine If B is loaded, then unloaded, then A is loaded, A works fine So, my belief is that when openssl is loaded it initializes some static members. Once a library that uses openssl is unloaded openssl clears some needed state that prevents anyone else from creating a security context.
暂时的解决方法如下：
SSL_CTX *ctx = NULL;
ctx = SSL_CTX_new(SSLv23_client_method());
if(ctx == NULL){
ERR_print_errors_fp(stdout);
InitOpenSSL();
ctx= SSL_CTX_new(SSLv23_client_method());
if(ctx == NULL){
ERR_print_errors_fp(stdout);
return HT_ERROR_INIT_ENGINE;
}
}
参考资料：
http://www.ibm.com/developerworks/cn/linux/l-openssl.html