使用感受

之前对Thrift的理解有点不准确，使用之后发现Thrift比想象中的要简单得多。

Thrift做的事情就是跨语言的分布式RPC，通过编写.thrift文件声明接口类和方法，client调用定义的方法，Server端实现定义的接口。尽管的确RPC是须要网络请求，但不像Netty这样的NIO网络编程库(还要关注许多传输数据中的细节，比方数据怎样序列化、怎样在字节数组里建立结构、怎样在两端解析字节数组、怎样处理Handler里的事件状态、怎样把多个Handler按顺序串起来)，Thrift掩盖了传输数据这件事情，开发人员使用的时候就是纯纯的RPC的使用感受。

基本使用

Thrift使用起来差点儿没有不论什么门槛，能够看这篇的文章，尽管有点老，可是看完之后基本使用起来没有不论什么障碍了。

官方给出的更加全面些，全面在.thrift文件中能够声明的东西列的更全些。

以下看看两个.thrift的定义：

shared.thrift

/** * This Thrift file can be included by other Thrift files that want to share * these definitions. */namespace java com.baidu.mordor.sink.servicestruct SharedStruct {  1: i32 key  2: string value}service SharedService {  SharedStruct getStruct(1: i32 key)}

tutorial.thrift

/** * The first thing to know about are types. The available types in Thrift are: * *  bool        Boolean, one byte *  byte        Signed byte *  i16         Signed 16-bit integer *  i32         Signed 32-bit integer *  i64         Signed 64-bit integer *  double      64-bit floating point value *  string      String *  binary      Blob (byte array) *  map
     
        Map from one type to another *  list
      
           Ordered list of one type *  set
       
             Set of unique elements of one type * * Did you also notice that Thrift supports C style comments? */// Just in case you were wondering... yes. We support simple C comments too./** * Thrift files can reference other Thrift files to include common struct * and service definitions. These are found using the current path, or by * searching relative to any paths specified with the -I compiler flag. * * Included objects are accessed using the name of the .thrift file as a * prefix. i.e. shared.SharedObject */include "shared.thrift"/** * Thrift files can namespace, package, or prefix their output in various * target languages. */namespace java com.baidu.mordor.sink.service/** * Thrift lets you do typedefs to get pretty names for your types. Standard * C style here. */typedef i32 MyInteger/** * Thrift also lets you define constants for use across languages. Complex * types and structs are specified using JSON notation. */const i32 INT32CONSTANT = 9853const map
        
          MAPCONSTANT = {'hello':'world', 'goodnight':'moon'}/** * You can define enums, which are just 32 bit integers. Values are optional * and start at 1 if not supplied, C style again. */enum Operation {  ADD = 1,  SUBTRACT = 2,  MULTIPLY = 3,  DIVIDE = 4}/** * Structs are the basic complex data structures. They are comprised of fields * which each have an integer identifier, a type, a symbolic name, and an * optional default value. * * Fields can be declared "optional", which ensures they will not be included * in the serialized output if they aren't set.  Note that this requires some * manual management in some languages. */struct Work {  1: i32 num1 = 0,  2: i32 num2,  3: Operation op,  4: optional string comment,}/** * Structs can also be exceptions, if they are nasty. */exception InvalidOperation {  1: i32 what,  2: string why}/** * Ahh, now onto the cool part, defining a service. Services just need a name * and can optionally inherit from another service using the extends keyword. */service Calculator extends shared.SharedService {   void ping(),   i32 add(1:i32 num1, 2:i32 num2),   i32 calculate(1:i32 logid, 2:Work w) throws (1:InvalidOperation ouch),   /**    * This method has a oneway modifier. That means the client only makes    * a request and does not listen for any response at all. Oneway methods    * must be void.    */   oneway void zip()}
        
       
      
     

Thrift通过IDL(接口定义语言)，在.thrift文件中声明接口类和方法，声明struct结构、const、Exception等，还能够include别的.thrift文件，这套语法与C很类似。通过编写IDL和generate代码，做到了不同语言之间的RPC，client实现接口类和使用结构类的时候很easy好用。

上面样例的代码能够从官方下载到，能够放到本地看一下他的使用，很easy。

Thrift重要组件

Thrift API里三个重要组成部分：Protocal，Transport，Server。

Protocal定义了消息怎样序列化。常见的是TBinaryProtocol，TJSONProtocol，TCompactProtocol。

Transport定义了消息在client和服务端怎样通信。常见的是TSocket，TFramedTransport，TNonblockingTransport等。

Server从transport端接收序列化后的消息，依据protocal反序列化回来，然后调用用户实现的消息handler(接口实现类)，最后把返回的数据序列化后再传回给client。常见的TServer为TSimpleServer，THsHaServer，TThreadPoolServer，TNonBlockingServer，TThreadedSelectorServer。以下会详细介绍各个Server的特点，开发人员须要选择适合自己场景的一套 Server+相应的Transport+相应的Protocol。

TServer说明

Thrift实现的几种不同的TServer。对于Java而言，版本号按0.9.0为准：

TSimpleServer在sever端仅仅有一个I/O堵塞的单线程，每次仅仅接受并服务一个client，适合測试使用，不能用于线上服务。

TNonblockingServer改动了TSimpleServer里堵塞的缺点，借助NIO里的Selector实现非堵塞I/O，同意多个client连接而且client能够使用select()选择。可是处理消息和select()的是同一个线程，当有大量client连接的时候，性能是不理想的。

 THsHaServer(半同步半异步server)在以上基础上，使用一个单独线程来处理网络I/O，一个worker线程池来处理消息。优点是仅仅要有空暇worker线程，消息能够被及时、并行处理，吞吐量会大一些。

TThreadedSelectorServer，与THsHaServer的差别是处理网络I/O也是多线程了，它维护两个线程池，一个负责网络I/O，一个负责数据处理。优点是当网络I/O是瓶颈的情况下，性能比THsHaServer更好。

TThreadPoolServer有一个专用的线程来接收connections，连接被建立后，会从ThreadPoolExecutor里取一个工作线程来负责这次连接，直到连接断开后线程回到线程池里，且线程池大小可配。也就是说，并发性的大小可依据服务器设定，假设不介意开许多线程的话，TThreadPoolServer是个还不错的选择。

全文完 :)