Fix #2068

Author: yhirose

httplib.h

@@ -7333,6 +7333,16 @@ inline ClientImpl::ClientImpl(const std::string &host, int port,
       client_cert_path_(client_cert_path), client_key_path_(client_key_path) {}
 
 inline ClientImpl::~ClientImpl() {
+  // Wait until all the requests in flight are handled.
+  size_t retry_count = 10;
+  while (retry_count-- > 0) {
+    {
+      std::lock_guard<std::mutex> guard(socket_mutex_);
+      if (socket_requests_in_flight_ == 0) { break; }
+    }
+    std::this_thread::sleep_for(std::chrono::microseconds{1});
+  }
+
   std::lock_guard<std::mutex> guard(socket_mutex_);
   shutdown_socket(socket_);
   close_socket(socket_);