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/2099Well 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.html1、配置 OpenLDAP 使用 SSL/TLS 加密数据通信 2、应用 openssl 工具进行 SSL 故障分析 3、使用 OpenSSL API 进行安全编程 4、使用 OpenSSL API 进行安全编程，第 3 部分: 提供安全服务 5、使用 OpenSSL API 进行安全编程，第 2 部分: 安全握手