Use and design of Muduo buffer class

Catalog

One 、Buffer Data structure of

Two 、Buffer The operation of

（1） Initial value

（2） towards Buffer Write in 200 byte

（3） from Buffer Read in 50 byte

（4） towards Buffer Write in 200 byte

（5） from Buffer Read in 350 byte

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muduo It's for Chen Shuo's personal use C++ Developed a network library , The code is of great learning value , The summary comes from books 《Linux Multithreaded server-side programming 》, Also written by Chen Shuo , Can cooperate with github Use code together .

muduo github website ：https://github.com/chenshuo/muduo

One 、Buffer Data structure of

 

muduo Designed buffer As a buffer for sending and receiving data ,Buffer Inside is a std::vector<char>, It's a piece of continuous memory , Two of them index,readIndex and writeIndex hold vector The content of is divided into three parts ：prependable、readable、writeable

 

prependable = readIndex;

readable = writeIndex-readIndex

writable = size() - writeIndex

Two 、Buffer The operation of

Suppose the sender sends two messages , The lengths are 50 Byte and 350 byte , The receiver receives the data twice , Every time 200 byte , Then subcontract , Call back the customer code twice , among readIndex and writeIndex Is initialized to 8,size() The initial value is 1032, This process Buffer The data structure changes of are as follows ：

（1） Initial value

 

（2） towards Buffer Write in 200 byte

 

（3） from Buffer Read in 50 byte

 

（4） towards Buffer Write in 200 byte

 

（5） from Buffer Read in 350 byte

 

At this time, all data has been read ,readIndex and writeIndex It will return to its original position for reuse .

muduo Buffer It also supports internal mobility , When readIndex More backward , Leave a huge prependable When space , If you write at this time and writeable Space is not enough ,Buffer Memory will not be reallocated , Instead, move the existing data to the front , Vacate writable Space .