Slacker cluster has a centralized registry, a zookeeper node, stores information of all the namespaces and servers instances in the cluster. Once a client declared remote functions, by calling `defn-remote` or `use-remote`, it reads all available servers offering that namespace from the registry and create connection to each of them. We the user issues a request, the client randomly pick up a connection from them. So the load is eventually distributed to every instance of slacker servers. And thanks to zookeeper’s notification feature, the client watches certain znode. It will be notified when 1. a connected server goes offline 2. a new server serving required namespace added into the cluster. Thus you don’t have to change client code or restart client when server changes.

To start a slacker server and add it to a cluster, you have to provide cluster information using the new :cluster option:

• :zk is the address of zookeeper node
• :name is a znode qualified string, to identify the cluster

On the client side, it’s important to use APIs from `slacker.client.cluster` instead of `slacker.client`:

If all servers provide ‘slacker.example.api go offline, slacker client will raise a “not-found” exception.

Slacker cluster is also designed with simple and clean in mind. You don’t have to change you business code to make it remote or cluster. Everything is transparent and non-invasive. Enjoy it.

One thing in slacker 0.6.x is you can expose multiple namespaces from a single server.

Suppose you have two namespaces `redday.stats` and `redday.api`, both contains functions you want to expose.

This will expose `redday.stats` and `redday.api` on port 6565.

On the client side, we have a new `use-remote` behaviors like clojure’s use. Instead of local one, it imports functions from a remote namespace to your current namespace.

If you need to configure callback to a particular function, you can still use `defn-remote` to specify the callback function. In slacker 0.6.0, a `:remote-ns` is required when you define such a remote function.

The complete code example (both server and client) can be found here.

In next post, I will explain another big new feature of 0.6.x, cluster support.

无暇去学习Android平台上繁琐的知识，不过好在有Phonegap这样的框架，可以把网页应用转化为本地应用，并且提供访问本地设备的API。通过Phonegap开发的程序还可以直接移植到iphone平台上。ClojureDocs Android就是运行在Phonegap中。

首页：

搜索界面

API函数界面

你可以从github获得代码和签名过的apk：https://github.com/sunng87/clojuredocs-android

Known Issue，phonegap程序在屏幕旋转时会崩溃，已经在2.3和3.2上重现，目前还不清楚具体的原因。(Edit 20120127: Fixed in 1.0.4)

欢迎任何的pull request。

LazyPress后台存储采用mongodb. 正是mongodb的schema free特性降低了项目功能重构的成本, 促进了人们更快更频繁地优化产品的模型. 这应该是文档型数据库之于传统关系型数据库最大的优势. (犹如git之于svn, 开分支的成本要低得多, 看似是一个普通的功能改进, 实则鼓励促进了开发人员通过开分支实现自己的修改)
LazyPress运行在最近发布的compojure 1.0.0和ring 1.0.0上, 打包为标准的Java web应用直接部署在cloudfoundry上. 前端继续使用的是我偏爱的Mootools库, 因为使用了很多新的浏览器技术, 所以目前只能保证在最新的Firefox和Chromium/Chrome上正常使用.

Fork me on github: http://github.com/sunng87/lazypress

Breaking Changes

• New maven coordinator: [slacker "0.4.0"] (groupId renamed to slakcer)
• defremote renamed to defn-remote
• SlackerException removed. slacker now uses slingshot for exception handling
• Rename :async option of defn-remote to :async?

What’s new in 0.4.0

• Add new serialization type :clj
• New interceptors: execution time stats, args logger, slow watch dog
• New HTTP interface
• Server inspect commands
• utility functions/macros defn-remote-all, defn-remote-batch and meta-remote

Get more information on github.

Like many server frameworks, slacker abstracts the request processing as a pipeline. The request object is modified by adding or updating attributes through each node of the pipeline. So it’s easy to add your interceptor into the pipeline, with which you can get the data before and after function executed.

To create such an interceptor, you should use the slacker.interceptor/definterceptor macro and slacker.interceptor/definterceptor+ macro:

(definterceptor name
:before interceptor-function
:after interceptor-function)

(definterceptor+ name [arguments]
:before interceptor-function
:after interceptor-function)

definterceptor+ can accept arguments so you can configure the interceptor when you use it.

See a simple example:

Then, add it to your slacker server by

Now you can log every function call of your slacker server.

For more detail about the interceptor framework, especially the request data, please check the wiki page.

In slacker 0.3.0, there is a built-in interceptor to stats function calls. You can find it at slacker.interceptors.stats. The stats data is expose via JMX. You can also write monitoring application to retrieve the data.

And there will be more built-in interceptors in 0.4.0, includes function call time stats and logging.

Connection Pool

Generally, pooling connection is a good idea in high concurrence application. To make slacker for real world, connection pool support is a high-prioritized feature in its development. The new connection pool is backended by commons-pool which you might familiar with. To use connection pool, just create slacker client with a new function `slackerc-pool`

Then you can use this pool just like a single client.

Some options are available to configure the pool by your wish:

• :max-active, max connections opened by the pool
• :exhausted-action
  • :fail throw an exception when pool exhausted.
  • :block block current thread and wait until max-wait exceed (throw an exception)
  • :grow automatically create new connection and add it to pool
• :max-wait max wait time before throwing an exception
• :min-idle minimal number of pool hold idle connections

The options are inherited from GenericObjectPool, you can find detailed information from their javadoc.

JSON Serialization

slacker just added json serialization provided by clj-json. According to my test, clj-json is 1x faster than carbonite in serialization.

However, with json serialization, you may lost some clojure types like keyword and set in type conversion. You should be caution when using json as serialization method.

In next release, I am planning to use fastjson as json lib which provides option to write type name into json so it could be a full featured serialization for clojure. And fastjson is claimed even faster than jackson.

Performance

slacker gains high performance with its non-blocking server, serialization and direct function call. As tested on a dual 6 core server, it reaches 10000+ TPS for a single client (50 connections, 50 threads). The server just use 35% CPU so I consider it could have even more TPS if there is two or more client machines.

So if you are interested in some benchmarks, you can test it with client like this. All the requests are using synchronous call because I believe it’s the most common case you use slacker.

Next steps

Inspired by discussion in cn-clojure mailing list, I’m going to add HTTP transport for slacker. With HTTP transport, it’s easier to debug and evaluate your clojure functions, it also makes slacker available to ClojureScript.

At lst, thanks Zach Tellman for reviewing my client code.

网站开通的第一时间，我提交了exaile-doubanfm-gnome-shell-extension，经过review和修改，这个扩展也得到了进一步的完善，适配了gnome-shell 3.2的风格。

你可以从这个地址直接安装启用
https://extensions.gnome.org/extension/24/exaile-doubanfm-control/

它会在exaile douban.fm启动后显示一个菜单在gnome-shell上，你可以通过这个菜单进行基本的操作。

如果喜欢，别忘了在extension.gnome.org上vote一下 ：）

In addition to APIs introduced in last post, asynchronous approach is supported in client API :

If you add option `:async` to defremote, then the function facade will return a promise. You have to deref it by yourself. Also you can use the `:callback` option in defremote to specify a callback function.

This gives you much more flexibility of using remote function. But be careful it will break consistency between local and remote mode.

To use slacker, add it to your project.clj

You can find examples on the github page.

这次的更新修正了长久依赖困绕用户登录问题，现在我们有一个专门的界面来输入验证码。这个功能要感谢DigitalPig用户在github的报告（鞭策作用），此外，我参考了豆瓣电台banshee插件的实现，节省了研究含验证码登录的时间，感谢。总而言之，没有用户的推动，这个项目也不会坚持这么久。

除此之外，插件还有一些支持了新的豆瓣说的推荐，优化了播放列表载入的策略。

另外值得highlight的是，对应的gnome-shell扩展发布了0.0.2版本，唯一的更新是专辑封面现在会显示在gnome-shell的菜单中。

你可以从github获得最新的插件和gnome-shell扩展：

• exaile-doubanfm-plugin 0.0.11-captcha: https://github.com/sunng87/exaile-doubanfm-plugin/downloads
• exaile-doubanfm-gnome-shell-extension 0.0.2: https://github.com/sunng87/exaile-doubanfm-gnome-shell-extension/tarball/0.0.2

安装豆瓣电台插件请参考这里。gnome-shell扩展直接解压至~/.local/share/gnome-shell/extensions/即可

有任何问题都可以在github或这里留言。