Made a temporary fix for OpenSSL thread problem

httplib.h

@@ -2029,15 +2029,23 @@ inline std::shared_ptr<Response> Client::post(const char* path, const Headers& h
 #ifdef CPPHTTPLIB_OPENSSL_SUPPORT
 namespace detail {
 
+// TODO: OpenSSL 1.0.2 occasionally crashes... The upcoming 1.1.0 is going to be thread safe.
+static std::mutex ssl_ctx_mutex_;
+
 template <typename U, typename V, typename T>
 inline bool read_and_close_socket_ssl(
     socket_t sock, bool keep_alive,
     SSL_CTX* ctx, U SSL_connect_or_accept, V setup,
     T callback)
 {
-    auto ssl = SSL_new(ctx);
-    if (!ssl) {
-        return false;
+    SSL* ssl = nullptr;
+    {
+        std::lock_guard<std::mutex> guard(ssl_ctx_mutex_);
+
+        ssl = SSL_new(ctx);
+        if (!ssl) {
+            return false;
+        }
     }
 
     auto bio = BIO_new_socket(sock, BIO_NOCLOSE);
@@ -2069,8 +2077,14 @@ inline bool read_and_close_socket_ssl(
     }
 
     SSL_shutdown(ssl);
-    SSL_free(ssl);
+
+    {
+        std::lock_guard<std::mutex> guard(ssl_ctx_mutex_);
+        SSL_free(ssl);
+    }
+
     close_socket(sock);
+
     return ret;
 }
 

test/test.cc

@@ -263,7 +263,7 @@ protected:
                 res.set_content("Hello World!", "text/plain");
             })
             .get("/slow", [&](const Request& /*req*/, Response& res) {
-                msleep(3000);
+                msleep(2000);
                 res.set_content("slow", "text/plain");
             })
             .get("/remote_addr", [&](const Request& req, Response& res) {
@@ -368,6 +368,9 @@ protected:
 
     virtual void TearDown() {
         svr_.stop();
+        for (auto& t: request_threads_) {
+            t.join();
+        }
         t_.join();
     }
 
@@ -380,6 +383,7 @@ protected:
     Server              svr_;
 #endif
     thread              t_;
+    std::vector<thread> request_threads_;
 };
 
 TEST_F(ServerTest, GetMethod200)
@@ -736,10 +740,10 @@ TEST_F(ServerTest, GetMethodRemoteAddr)
 
 TEST_F(ServerTest, SlowRequest)
 {
-    std::thread([=]() { auto res = cli_.get("/slow"); }).detach();
-    std::thread([=]() { auto res = cli_.get("/slow"); }).detach();
-    std::thread([=]() { auto res = cli_.get("/slow"); }).detach();
-    msleep(1000);
+    request_threads_.push_back(std::thread([=]() { auto res = cli_.get("/slow"); }));
+    request_threads_.push_back(std::thread([=]() { auto res = cli_.get("/slow"); }));
+    request_threads_.push_back(std::thread([=]() { auto res = cli_.get("/slow"); }));
+    msleep(100);
 }
 
 #ifdef CPPHTTPLIB_ZLIB_SUPPORT