socket Blocking and non blocking modes

This article discusses Linux Under the socket Socket

One 、 Sync 、 Asynchronous blocking and non blocking

1. Sync ： Ask and wait IO How the operation is completed
2. asynchronous ： After actively requesting data , You can handle other tasks , Then wait IO Notice of completion of operation
3. Blocking ： The thread continues to wait for the data in the resource to be ready , Until a response is returned
4. Non blocking ： The thread returns the result directly , Does not wait for the resource to prepare the data before responding to the result

summary ：

• Synchronous and asynchronous refer to IO operation , Synchronization is the thread waiting IO Completion , Induction is IO Upon completion, the thread will receive a notification
• Blocking and non blocking are threads , Blocking may occur at IO period , It can also happen in IO Before

for example , For a simple server program （socket、bind、listen、accept）, We usually say that the program will block in accept() It's about , and accept() The operation of the function is synchronous

Two 、 What is? socket Blocking / Non-blocking mode ?

1） Establishing a connection connect

• Blocking mode ,connect First send SYN Request to server , When the client receives a message from the server SYN When confirming , be connect return , Otherwise, it will be blocked all the time .

• Non blocking mode ,connect Will enable TCP Three handshakes of the agreement , however connect The function does not wait for the connection to be established before returning , It's about going back to , The error code returned is EINPROGRESS, Indicates that a process is in progress .

2） Receiving connection accept

• Call... In blocking mode accept() function , When there is no new connection , The process goes to sleep , Until a connection is available , To return to .
• Call... In non blocking mode accept() The function immediately returns , There are connections that return client socket descriptors . When there is no new connection , Will return EWOULDBLOCK Error code , It means that it should have been blocked .

3） Read and write operations read/write

• When the read / write buffer is filled , In blocking mode, the program will block in read/write, Instead of blocking mode read/write The error code will be returned directly

3、 ... and 、 How to set up socket Blocking / Non-blocking mode ?

• socket() Function created socket The default is blocking Of
• socket() The function prototype ：

int socket(int domain, int type, int protocol);

/*1.domain： Protocol domain , Also known as protocol family , It determines socket Address type of  * 2.type： Appoint socket type , It is associated with protocol Corresponding  * 3.protocol： Specify transport protocol , Such as IPPROTO_TCP The specified transport protocol is TCP,IPPTOTO_UDP The specified transport protocol is UDP, When protocol by 0 when , Will automatically select type Default protocol corresponding to type  */

• take socket Setting to non blocking mode has Two kinds of Way :

1. stay establish socket when , Specify the created socket Non blocking （type Parameter SOCK_NONBLOCK sign ）

int sockfd = socket(AF_INET, SOCK_STREAM | SOCK_NONBLOCK, IPPROTO_TCP);

2. Use fcntl() and ioctl() Function settings socket Is non-blocking mode

fcntl(sockfd, F_SETFL, fcntl(sockfd, F_GETFL, 0) | O_NONBLOCK);  
   
ioctl(sockfd, FIONBIO, 1);  //1: Non blocking  0: Blocking