Writing Concurrent Programs Using F# Mailbox Processors

NOTE:

1、这篇文章关于actor model的解释是非常好的，正是这个原因，才收录了这篇文章

2、F# Mailbox Processors 其实就是actor model中的actor

There are many approaches to concurrency, but in this issue, I’d like to talk about the built-in way that F# can handle message-based concurrency: using F# mailbox processors.

The Actor Model

To understand F# mailbox processors better, let’s look a little closer at the theory they’re based on: the actor model, which is also a prominent part of the Erlang programming language. There are a few key parts of the theory that can help you know when and why you should be using mailbox processors.

The Actor Model is a model of concurrent programming that uses actors as the base unit. These actors are lightweight constructs that contain a queue, and can receive and process messages.

NOTE:

1、到处都可以看到message queue

2、既然使用了message queue，那么它肯定是 asynchronous

When I say lightweight, I mean lightweight—they’re not like threads. I can easily spin up 100,000 on my aging laptop without a hitch. An actor’s behavior is very limited. They can only:

1、Create more actors

2、Determine what to do with the next incoming message

3、Send messages to another actor

There are also a few rules for the actor model itself:

1、Actors can be created dynamically.

2、The only interaction between actors is through direct asynchronous message passing.

3、Messages must include the actor’s address.

4、There’s no restriction on message arrival order.

A mailbox processor is based on a single actor. However, in general, you’ll want to create several actors as part of a system. Even one of the creators of the actor model, Carl Hewitt, has famously said, "One actor is no actor. They come in systems."

Erlang actor analogy

NOTE:

1、下面的类比是非常好的

I mentioned Erlang above as the first, and most faithful, representation of the actor model, because this gives you a good idea how to think about a whole system of actors. Erlang was developed for telephony applications, and you can think about a telephone as a single actor that can send messages (or make calls) to another telephone, as long as you have an address (telephone number). This analogy gives you a good working idea of how to build systems of actors, or mailbox processors.

Actor, mailbox processor, and agent

NOTE:

1、三者其实是相同的含义。

Here’s one more note before I jump into code. The original model is called the actor model and uses actors. F#’s implementation of actors is referred to as mailbox processors, as I’ve mentioned. Actors and mailbox processors are also occasionally referred to as agents. For most uses, these terms are interchangeable.

For most purposes, the terms actor, mailbox processor, and agent are interchangeable.