This sample demonstrates a simple social network pub/sub system, with short text messages being sent between users. Publishers send out short "Chirp" messages (not to be confused with "Tweets", for a variety of legal reasons) to any other users that are following them.
The sample consists of two applications, Chirper.Server which hosts Orleans and all of the grains, and Chirper.Client which hosts an Orleans client and the terminal interface seen in the above screenshot.
The sample demonstrates the following features of Orleans:
- Grain persistence - for storing the state of a grain in a database
- Reentrant grains - for allowing multiple calls to concurrently interleave each other
- Grain observers - for sending push messages back to clients
In this project, in-memory persistence is used (see Program.cs), but it can be substituted for a persistence provider of your choice without changing the grain code.
Only the configuration needs to change in order to use a different persistence provider.
Orleans allows the network of Chirper users to be described via very simple C# code whilst allowing it to easily scale out to handle increasing number of users and volume of chirp messages.
Chirper users are modeled as grains.
By modeling each user as a grain, messaging load is distributed, with each grain handling the forwarding of messages generated by that user to any other users that are following them.
The grains implement three different grain interfaces to represent the three functional facets of those entities - IChirperPublisher, IChirperSubscriber and IChirperAccount
There is also an IChirperViewer observer interface for applications to subscribe for status changes from a particular Chirper user without becoming a Follower. This observer interface is typically used when writing client UI applications such as ChirperClient.