Extension point for injecting custom instance of `IConnectionMultiplexer`

[footcha]

I would like to have full control of how an instance of StackExchange.IConnectionMultiplexer is created. Typically I have registered the multiplexer in IoC container in my application. I would like to reuse the process of creating the instance and to have more control over its lifecycle.

Suggested solution

New configuration parameter connectionMultiplexerFactoryType will contain type that implements IConnectionMultiplexerFactory:

public interface IConnectionMultiplexerFactory
{
    /// <summary>
    /// This method provides either new or already existing instance of <see cref="IConnectionMultiplexer"/>.
    /// </summary>
    /// <returns>Fully configured connection multiplexer</returns>
    IConnectionMultiplexer CreateMultiplexer();

    /// <summary>
    /// When <see cref="RedisSessionStateProvider"/> fails with <see cref="RedisConnectionException"/>
    /// then it sends to <see cref="IConnectionMultiplexerFactory"/> and attempt to cleanup a failed multiplexer.
    /// Additionally, the factory itself is responsible for providing a clean, fresh instance of IConnectionMultiplexer (it can be the same instance).
    /// </summary>
    /// <param name="connectionMultiplexer">Instance that failed with <see cref="RedisConnectionException"/></param>
    /// <returns>New or refreshed instance</returns>
    IConnectionMultiplexer RestartMultiplexer(IConnectionMultiplexer connectionMultiplexer);
}

[ricardomomm]

Please, this is very important, specially as Azure Redis Cache uses the number of clients connected as base for subscription layers/prices.