Connecting to multiple Redis servers

In the previous post, I have showed how I designed a simple C++ wrapper class that uses a standard C++11 unique_ptr to help working with the hiredis context in such a scenario. My solution has a few limitation, first of them, it doesn't allow to connect to more than a Redis server. Often this is "as designed", still sometimes it is just a nuisance. In any case it is not difficult to redesign the code to allow connections to many Redis servers.

I have written a class named SharedRedis that wraps the hiredis functionality, storing the Redis connection in a C++11 standard shared_ptr smart pointer. You could find the full include file on github.
typedef std::shared_ptr<redisContext> SharedContext; // 1

class SharedRedis
{
    enum { DEFAULT_PORT = 6379 }; // 2
public:
    SharedRedis(const std::string& server, int port = DEFAULT_PORT); // 3
    SharedRedis(int port = DEFAULT_PORT) : SharedRedis("localhost", port) {}

    // ...
private:
    // ...
    SharedContext spContext_;
};
1. To keep the code more readable, I typedef'ed the shared pointer to the Redis context.
2. In this implementation, the user should specify host and port for the Redis server, by default the standard Redis port is used.
3. The only substantial difference to the UniqueRedis implementation (beside the usage of a different smart pointer) is that the object is freely built by the user. No static initializer, but just normal ctors are called to create a new object.

There is not much to say about the implementation, that is very close to what we have seen for the UniqueRedis version. You could see the full source code on github. Maybe it could be worthy to spend a few words on the shared smart pointer construction/destruction.
SharedRedis::SharedRedis(const std::string& server, int port)
{
    // ...
    spContext_ = SharedContext(context, std::bind(&SharedRedis::free, this)); // 1
}

void SharedRedis::free() // 2
{
    redisFree(spContext_.get());
}
1. In the class constructor, the context smart pointer is initialized passing the raw context pointer (we have ensured before that it is a valid value) and the function that has be called on its destruction. Here I use a method of the same class, I could have passed the native radisFree() function, but I wanted to add some stuff to its implementation (actually, just some logging, but I guess it is interesting to show the idea). That's way I had to bind the SharedRedis::free() function to the this pointer, so that the SharedContext destructor could be able to call the right function on the right object.
2. Here is the function that we want to be called on the SharedContext destruction.

There is still something missing. Probably, if we have many Redis connection we want to play with, we should think of storing them in a collection (maybe a map, using as key the host/port), so to have a centralized place to manage them consistently. But I guess this could be seen in another post.

No comments:

Post a Comment