.net – a service bus and when do I need one

netnservicebusservicebus

I have heard talk about the NServiceBus, but I haven't really understood what it is. They claim to be "The most popular open-source service bus for .net".

What is a service bus, and when do I need one?

Best Answer

You can think of a service bus as the Ethernet of SOA.

First and foremost, it introduces a language of identifying things, like an IP address in Ethernet. This name isn't something inherently physical.

Next, you have something physical involved on each node, like a queue in the case of a bus for supporting semi-connected communication, or an Ethernet card in the metaphor.

Beyond just the physical, there is the "protocol" part of the communication, like the OSI stack for Ethernet. With the bus, this is the client libraries used by application code.

Ultimately, you can view a service bus as providing the next higher level of abstraction for building distributed systems. You can use it also for client-server communication to give you durable one-way messaging as well as for the server to push notifications back to the client.

Specifically, you'll find NServiceBus to be quite lightweight and easy to use once you make peace with its use of queuing technology - your choice of RabbitMQ, MSMQ, Regular SQL Tables, Amazon SQS, Azure Storage Queues, and Azure Service Bus.

This is the style that Microsoft tends to use in their examples.

It appears that the guidance in this area may have changed, as StyleCop now enforces the use of the C# specific aliases.

C# – the difference between const and readonly in C#

Apart from the apparent difference of

having to declare the value at the time of a definition for a const VS readonly values can be computed dynamically but need to be assigned before the constructor exits.. after that it is frozen.
const's are implicitly static. You use a ClassName.ConstantName notation to access them.

There is a subtle difference. Consider a class defined in AssemblyA.

public class Const_V_Readonly
{
  public const int I_CONST_VALUE = 2;
  public readonly int I_RO_VALUE;
  public Const_V_Readonly()
  {
     I_RO_VALUE = 3;
  }
}

AssemblyB references AssemblyA and uses these values in code. When this is compiled:

in the case of the const value, it is like a find-replace. The value 2 is 'baked into' the AssemblyB's IL. This means that if tomorrow I update I_CONST_VALUE to 20, AssemblyB would still have 2 till I recompile it.
in the case of the readonly value, it is like a ref to a memory location. The value is not baked into AssemblyB's IL. This means that if the memory location is updated, AssemblyB gets the new value without recompilation. So if I_RO_VALUE is updated to 30, you only need to build AssemblyA and all clients do not need to be recompiled.

So if you are confident that the value of the constant won't change, use a const.

public const int CM_IN_A_METER = 100;

But if you have a constant that may change (e.g. w.r.t. precision).. or when in doubt, use a readonly.

public readonly float PI = 3.14;

Update: Aku needs to get a mention because he pointed this out first. Also I need to plug where I learned this: Effective C# - Bill Wagner

Best Answer

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C# – the difference between String and string in C#

This is the style that Microsoft tends to use in their examples.

C# – the difference between const and readonly in C#

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