libpqxx freezes on connection::prepare - c++

Question

My program should synchronize with remote postgres database. My code:
db_handler::DB_Handler::DB_Handler(const char* host, unsigned int port, const char* db, const char* user, const char* password, int& error) {
...
this->password = reinterpret_cast<char*>(malloc(std::strlen(password) + 1));
strcpy(this->password, password);
this->connection = nullptr;
if (this->connect_to_db() != 0) {
error = 1;
}
else {
error = 0;
}
}
int db_handler::DB_Handler::connect_to_db() {
try {
std::string connection_params = "host=";
connection_params += std::string(host);
...
connection_params += " password=";
connection_params += password;
if (this->connection != nullptr) {
delete this->connection;
}
this->connection = new pqxx::connection(connection_params.c_str());
return 0;
}
catch (...) {
return 1;
}
}
int db_handler::DB_Handler::sync() {
for (int tries = 0; tries < 2; tries++) {
try {
this->connection->prepare("get_keys", "*query here*");
...
}
catch (const pqxx::broken_connection& e) {
this->connect_to_db();
std::this_thread::sleep_for(std::chrono::milliseconds(50));
}
catch (...) {
return 1;
}
}
return 1;
}
And on this row this->connection->prepare("get_keys", "*query here*"); my program freezes forever until I will restart it.
Where am I wrong and how can I fix it?
Maybe I should add some timeouts? How can I do it?