shibd commented on PR #170:
URL:
https://github.com/apache/pulsar-client-cpp/pull/170#issuecomment-1396581433
> In short, a natural design is to save the `ServiceUrlProvider` in `Client`
and call `getServiceUrl()` method (in C++ it's just a function invocation) each
time we need a service URL. Maybe we need to maintain a key-value (`serviceUrl
-> ServiceNameResolver`), when the `serviceUrlProvider()` returns a different
result from the key, creating a new `ServiceNameResolver` for related lookup
requests.
I think you only need the client to provide the `updateServiceUrl` method.
Users can take advantage of this approach to implement their own services.
(Pseudocode)
```c++
class Store;
class AutomaticClusterService {
public:
explicit AutomaticClusterService(const Store& store, const Client
pulsarClient)
: store_(store), pulsarClient_(pulsarClient) {
serviceUrlCache_ = store.queryServiceUrl();
updateServiceUrlInterval_ = boost::posix_time::seconds(60);
runUpdateServiceurl();
}
void start() {
runUpdateServiceurl();
}
const std::string& getServiceUrl(){
return serviceUrlCache_;
}
const void runUpdateServiceurl() {
timer_->expires_from_now(updateServiceUrlInterval_);
auto availableServiceUrl = store_.queryServiceUrl();
timer_->async_wait([this](const boost::system::error_code& ec) {
// Maybe some other implementation
if (serviceUrlCache_ != availableServiceUrl) {
serviceUrlCache_ = availableServiceUrl;
pulsarClient_.updateServiceUrl(serviceUrlCache_);
}
runUpdateServiceurl();
});
}
private:
// External storage services
Store store_;
const Client pulsarClient_;
std::string serviceUrlCache_;
std::shared_ptr<boost::asio::deadline_timer> timer_;
boost::posix_time::time_duration updateServiceUrlInterval_;
};
Store store;
Client client(store.queryServiceUrl());
AutomaticClusterService automaticClusterService(store, client);
automaticClusterService.start();
//....
```
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