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One 、 brief introduction

         The last article combines echo The server side introduces server How was it created , Next, let's look at how to send data after establishing a connection .
         The last article also used this picture , In the middle of the channel That's what we're going to talk about today . The data transmission will be explained in more detail later .

First ,channel What is it? ？
channel, Channels can also be called pipes . It can read and write at the same time , And streams can only read or write , passageway （Channel） It's two-way , Can read operation , You can also write operations .
Channels can read and write data asynchronously .
Channels can read data from the buffer , You can also write data to the buffer .
We see the following client.cpp in , That's what I used channel Realize data interaction . ad locum , The channel represents the communication line from the client to the server .

So this article makes a simple analysis of the channel .

Two 、 The code analysis

First of all channel Base class of , You can see all the channel Are based on protobuf Of RpcChannel and Describable, There are two functions that need to be implemented ,Weight() On behalf of the current Channel The weight of ,CheckHealth() health examination . It's a virtual function because channel There are many forms , such as SelectiveChannel、PartitionChannel etc. .

Then realize ChannelOptions class , Yes channel Summarize the options of .
such as connect_timeout_ms Yes, the connection timed out , Note that the timeout is rpc The connection inside the framework timed out .
timeout_ms The control is once rpc Requested timeout .
The notes are very detailed , I won't list them all .

stay channel.cpp The default parameters are given in .

And then look channel The initialization . Also overloaded multiple versions , It's all called to InitSingle().

The key content is here .GlobalInitializeOrDie() Perform operations such as protocol and load balancing method registration , The global only needs to be executed once . Then this server_addr_and_port Insert into socketmap And put the corresponding socket_id Save to _server_id For subsequent use ,socketmap Save sth IP+port To socket_id Correspondence of .

Then there is the most important and core CallMethod Method . All operations involving pipes will be completed by calling this function here . Every request is bound with a controller, First, initialize according to the passed in attributes cntl, Then set the protocol and retry mechanism , Subsequent operations are basically carried out around it .

This was followed by a response to this request controller Make relevant assignment , It is mainly divided into two parts , First, if each timeout parameter is not set , Just use _options Parameters of , In particular, the connection timed out , As the note says , Because the connection is all rpc Call frequently used , Alone for cntl Setting doesn't make sense , So direct use _options Inside . The second is related to the actual content of this request response、 Packing function 、 Called methods, etc .

Next set up timer And the current request completed _deadline_us, Overtime and backup_request_ms All need to wait timer. There are three situations , One is backup_request_ms Set valid conditions , Second, there is no effective backup_request_ms But there are effective timeout_ms Local conditions , Third, the situation of neither .
The first case will use HandleBackupRequest Set up a for backup_request Of bthread_timer, That is, how long will it take to launch backup request , Will also make use of timeout_out formation deadline_us.（ This Handle And the next Handle All belong to the category of system call ）

The second is only timeout , Use HandleTimeout As a setting bthread_timer and deadline_us, Processing timeout required after arrival .

When everything is set . You can submit the transmission . Use of is cntl->IssueRPC(), This function is analyzing controller I'll explain it in detail when . The core method is actually through the processing of various settings , Finally, after completing the sending of a request .

Finally, the two methods that implement the base class , It's just a normal channel class .
Weight stay controller Yes lb You'll get his value when you , It is 0. That is, at present Channel All connected server And .
Ordinary Channel Of CheckHealth() By judging the corresponding _lb Whether it can be connected to a valid server Realized .

summary

That's all for today , This paper mainly combines how to send data to channel Detailed source code analysis , Later blogs will continue to analyze other codes .