DataCenter

datacenter 可用来在整个 skynet 网络做跨节点的数据共享。

Datacenter can be used for data sharing across nodes over the whole Skynet network.

当你需要跨节点通讯时，虽然只要持有其它节点的地址，就可以发送消息。但地址如何获得，却是一个问题。

When you need across nodes data transmission, you only need the address of the other node to send a message, but it's a problem on how to get this address.

早期的 skynet 提供了具名服务的特性，可以给一个服务起一个唯一的名字，用名字即可发送消息。但目前更推荐的做法是通过 datacenter 或 UniqueService。

In the early implementation of Skynet, it offers a naming service, from the name you can tell it assigns each service a unique name and send messages with that name. But now the most recommended way is to send it over Datacenter or use UniqueService.

datacenter 类似一个全网络共享的注册表。它是一个树结构，任何人都可以向其中写入一些合法的 lua 数据，其它服务可以从中取出来。所以你可以把一些需要跨节点访问的服务，自己把其地址记在 datacenter 中，需要的人可以读出。

Datacenter is similar to a shared registry for the network. It's in tree struct, anybody can write data in with valid Lua format, the other services can get data from there. So you can put the address of services that require across nodes data sharing in Datacenter and data consumer can read it.

datacenter 是一个 lua 库，使用：

Datacenter is a Lua lib, use:

local datacenter = require "skynet.datacenter"

可以进入。

to get in.

一共有三个方法：

There are three ways to use it:

datacenter.set(key1, key2, ... , value) 可以向 key1.key2 设置一个值 value 。这个 api 至少需要两个参数，没有特别限制树结构的层级数。

datacenter.set(key1, key2, ... , value) set key1, key2... with value. this API requires at least two parameters, there is no limitation on how many levels of the tree.

datacenter.get(key1, key2, ...) 从 key1.key2 读一个值。这个 api 至少需要一个参数，如果传入多个参数，则用来读出树的一个分支。

datacenter.get(key1, key2, ...) get the value from key1, key2... this API requires at least one parameter, if multiple values are passed in, it'll return the branch of the tree.

datacenter.wait(key1, key2, ...) 同 get 方法，但如果读取的分支为 nil 时，这个函数会阻塞，直到有人更新这个分支才返回。当读写次序不确定，但你需要读到其它地方写入的数据后再做后续事情时，用它比循环尝试读取要好的多。wait 必须作用于一个叶节点，不能等待一个分支。

datacenter.wait(key1, key2, ...) similar to get, but if the branch is nil, it will be blocked until there is an update in this branch. When read-write is not in order but you need to wait until you get the data of a specified node, it's better to use it than polling reading. wait has to be on a leave node not on a branch.

注意：这三个 api 都会阻塞住当前 coroutine ，留心异步重入的问题。

Note: these 3 API will block the current coroutine. be careful on the reentrant async problem.

和 UniqueService 相比较，datacenter 使用起来更加灵活。你还可以通过它来交换 Multicast 的频道号等各种信息。但是，datacenter 其实是通过在 master 节点上部署了一个专门的数据中心服务来共享这些数据的。所有对 datacenter 的查询，都需要和中心节点通讯（如果你是多节点的架构的话），这有时会造成瓶颈。如果你只需要简单的服务地址管理，UniqueService 做的更好，它会在每个节点都缓存查询结果。

Compared to UniqueService, datacenter is more flexible. You can use it to exchange the channel info of Multicast. However, Datacenter set a data-sharing service on the master node to achieve data sharing. Querying Datacenter requires communications with the master node (if you are using a multiple nodes framework), which might cause a bottleneck sometimes. If you only need simple data addressing management, UniqueService would be a better choice, it'll cache the querying results on each node.

在cluster模式下使用 Use in cluster mode

该功能在cluster模式下不能直接使用，需要自己实现。

this feature is not available in cluster mode, use needs to implement it.