Active object pattern

Herb Sutter Effective Concurrency: Prefer Using Active Objects Instead of Naked Threads

非常好的文章，已经收录了。

wikipedia Active object

The active object design pattern decouples method execution from method invocation for objects that each reside in their own thread of control.[1] The goal is to introduce concurrency, by using asynchronous method invocation and a scheduler for handling requests.[2]

NOTE:

1、结合下面的例子来看，上面这段话的意思其实是method invocation只是往queue中添加了一个request/message，method execution在另外一个thread中进行；

2、 这个名称的由来是什么？何为active？在 rosettacode Active object 中对这个问题进行了解释

3、其实我编写的很多multithread application都可以归入到active object pattern的范畴

The pattern consists of six elements:

• A proxy, which provides an interface towards clients with publicly accessible methods.
• An interface which defines the method request on an active object.
• A list of pending requests from clients.
• A scheduler, which decides which request to execute next.
• The implementation of the active object method.
• A callback or variable for the client to receive the result.

Example

NOTE:

1、原文给出的是Java的例子

stackoverflow Explain “Active-object” pattern

comments

Active-object is the Command Pattern, implemented concurrently.

A

NOTE: 1、非常形象生动的比喻

2、结合下面的比喻来理解wikipedia Active object中的内容

The Active object pattern's goal is to separate the method calling from method execution. It is like a waiter in a restaurant, who just hands the orders from the customers to the chef.

When a customer orders some food from the waiter

the customer is the Client, the waiter is the Proxy

he writes it up on a paper (obviously doesn't start to cook it),

the paper is the MethodRequest, the table's number on the paper is the Future object

gives the paper to the chef, who decides which cook should prepare it (who has time).

the chef is the Scheduler who has a list of papers (ActivationList) and the cooks are the Servant-s

NOTE:

1、**ActivationList**其实对应的就是queue

When the meal is ready, the cook places it on the serve bar and the waiter brings it to the customers table.

Client reads the method's result, from the Result object.

Implementation

1、需要一个message queue。

TODO

1、wikipedia Active object

2、stackoverflow To use Active object or not?

3、https://sites.google.com/site/kjellhedstrom2/active-object-with-cpp0x