code snippets for "Using Copy-On-Write In Multithreaded Code To Reduce Locking Overhead" post

s1.cs

public class TenantSessionFactoryManager : ITenantSessionFactoryManager
{
    private readonly ITenantContext tenantContext;
    private readonly ITenantInfoHolder tenantInfoHolder;
    private readonly string mappingAssemblyName;

    private readonly object writeLock = new object();
    private Dictionary<Guid, ISessionFactory> sessionFactories;

    public TenantSessionFactoryManager(ITenantContext tenantContext, ITenantInfoHolder tenantInfoHolder, string mappingAssemblyName)
    {
        this.tenantContext = tenantContext;
        this.tenantInfoHolder = tenantInfoHolder;
        this.mappingAssemblyName = mappingAssemblyName;
        sessionFactories = new Dictionary<Guid, ISessionFactory>();
    }

    public ISession CreateSessionForCurrentTenant()
    {
        var tenantId = tenantContext.CurrentTenantId;

        if (!sessionFactories.ContainsKey(tenantId))
        {
            CreateSessionFactoryForCurrentTenant();
        }

        return sessionFactories[tenantId].OpenSession();
    }

    private void CreateSessionFactoryForCurrentTenant()
    {
        lock (writeLock)
        {
            var tenantId = tenantContext.CurrentTenantId;

            if (!sessionFactories.ContainsKey(tenantId))
            {
                var connectionString = tenantInfoHolder.GetDatabaseConnectionString(tenantId);

                var sessionFactory = new Configuration()
                    .Configure()
                    .AddProperties(new Dictionary<string, string>
                            {
                                { "connection.connection_string", connectionString },
                                { "cache.region_prefix", "Tenant_" + tenantId }
                            })
                    .AddAssembly(mappingAssemblyName)
                    .BuildSessionFactory();

                var newDictionary = new Dictionary<Guid, ISessionFactory>(sessionFactories);
                newDictionary[tenantId] = sessionFactory;
                sessionFactories = newDictionary;
            }
        }
    }

    public void RemoveSessionFactoryForTenant(Guid tenantId)
    {
        if (!sessionFactories.ContainsKey(tenantId))
        {
            return;
        }

        lock (writeLock)
        {
            if (!sessionFactories.ContainsKey(tenantId))
            {
                return;
            }

            var sessionFactory = sessionFactories[tenantId];
            var newDictionary = new Dictionary<Guid, ISessionFactory>(sessionFactories);
            newDictionary.Remove(tenantId);
            sessionFactories = newDictionary;

            sessionFactory.Dispose();
        }
    }
}

s2.cs

if (sessionFactories.ContainsKey(tenantId))
{
    return sessionFactories[tenantId].OpenSession();
}

s3.cs

private void CreateSessionFactoryForCurrentTenant()
{
    lock (writeLock)
    {
        var tenantId = tenantContext.CurrentTenantId;

        if (!sessionFactories.ContainsKey(tenantId))
        {
            var connectionString = tenantInfoHolder.GetDatabaseConnectionString(tenantId);

            var sessionFactory = new Configuration()
                .Configure()
                .AddProperties(new Dictionary<string, string>
                        {
                            { "connection.connection_string", connectionString },
                            { "cache.region_prefix", "Tenant_" + tenantId }
                        })
                .AddAssembly(mappingAssemblyName)
                .BuildSessionFactory();

            var newDictionary = new Dictionary<Guid, ISessionFactory>(sessionFactories);
            newDictionary[tenantId] = sessionFactory;
            sessionFactories = newDictionary;
        }
    }
}

s4.cs

public void RemoveSessionFactoryForTenant(Guid tenantId)
{
    if (!sessionFactories.ContainsKey(tenantId))
    {
        return;
    }

    lock (writeLock)
    {
        if (!sessionFactories.ContainsKey(tenantId))
        {
            return;
        }

        var sessionFactory = sessionFactories[tenantId];
        var newDictionary = new Dictionary<Guid, ISessionFactory>(sessionFactories);
        newDictionary.Remove(tenantId);
        sessionFactories = newDictionary;

        sessionFactory.Dispose();
    }
}

s5.cs

public void RemoveSessionFactoryForTenant(Guid tenantId)
{
    lock (writeLock)
    {
        if (!sessionFactories.ContainsKey(tenantId))
        {
            return;
        }

        var sessionFactory = sessionFactories[tenantId];
        var newDictionary = new Dictionary<Guid, ISessionFactory>(sessionFactories);
        newDictionary.Remove(tenantId);
        sessionFactories = newDictionary;

        sessionFactory.Dispose();
    }
}

s6.cs

public ISession CreateSessionForCurrentTenant()
{
    var tenantId = tenantContext.CurrentTenantId;

    if (!sessionFactories.ContainsKey(tenantId))
    {
        CreateSessionFactoryForCurrentTenant();
    }

    return sessionFactories[tenantId].OpenSession();
}