連接遠程服務時,如果沒有直接提供ip,只有域名,就需要使用gethostbyname或者getaddrinfo來解析出ip地址,這一過程需要dns訪問,是阻塞的。在webrtc的例子peer_connection_client.cc代碼中,給出了使用rtc::AsyncResolver獲取ip地址的方法,值得效仿。
void PeerConnectionClient::Connect(const std::string& server,
int port,
const std::string& client_name) {
RTC_DCHECK(!server.empty());
RTC_DCHECK(!client_name.empty());
if (state_ != NOT_CONNECTED) {
RTC_LOG(WARNING)
<< "The client must not be connected before you can call Connect()";
callback_->OnServerConnectionFailure();
return;
}
if (server.empty() || client_name.empty()) {
callback_->OnServerConnectionFailure();
return;
}
if (port <= 0)
port = kDefaultServerPort;
server_address_.SetIP(server);
server_address_.SetPort(port);
client_name_ = client_name;
if (server_address_.IsUnresolvedIP()) {
state_ = RESOLVING;
resolver_ = new rtc::AsyncResolver();
resolver_->SignalDone.connect(this, &PeerConnectionClient::OnResolveResult);
resolver_->Start(server_address_);
} else {
DoConnect();
}
}
void PeerConnectionClient::OnResolveResult(
rtc::AsyncResolverInterface* resolver) {
if (resolver_->GetError() != 0) {
callback_->OnServerConnectionFailure();
resolver_->Destroy(false);
resolver_ = NULL;
state_ = NOT_CONNECTED;
} else {
server_address_ = resolver_->address();
DoConnect();
}
}
它實現了異步的調用方式,感興趣的話可以進一步看看rtc::AsyncResolver實現的源碼。