Actor programming with MailboxProcessor

The actor programming model is a concurrent programming technique that provides a powerful mechanism to encapsulate several concurrency features. The key principles of the actor model are as follows:

• No shared state between actors
• Async message passing between clients to actor or between actors
• Mailbox to buffer incoming messages
• React to received messages by executing function

The F# MailboxProcessor class is the implementation of the actor model in FSharp.Core, and it is essentially a dedicated message queue running its own thread. We can use the API for MailboxProcessor to Post/Receive messages synchronously or asynchronously. We can also consider it an agent with an internal state machine. Let's take look at our first async agent:

let agent = 
   MailboxProcessor.Start(fun inbox -> 
     async { while true do 
               let! msg = inbox.Receive() 
               printfn "got message '%s'" msg } ) 
> agent.Post "Hello...