Network Programming socket-Overview of TCP select

I/O model:

1. Blocking I/O model

2. Non-blocking I/O model: Use fcntl to set the socket to non-blocking, and then round-robin to read data, which will consume a lot of CPU time;

3. I/O multiplexing model: blocking on select;

4. Signal-driven I/O model:

5. asynchronous I/O model: aio_read. The signal is generated only when the data has been copied to the application process buffer.

Select:

The last time parameter of select:

1. If it is null, it indicates that it will wait forever;

2. If the specific time is not 0, it indicates that the return time cannot exceed this time;

3. The second and microsecond values in the struct are both 0, indicating no waiting, that is, polling;

The first parameter of select refers to the number. It is the maximum descriptor to be tested plus 1, because the descriptor starts from 0 and its maximum value is specified by fd_setsize, to increase the descriptor set size, you must first increase the value of fd_setsize and then re-compile the kernel;

Each time the SELECT statement is re-called, all the locations in the descriptor set must be set to 1, because 2, 3, and 4 parameters are value-result parameters, when the function returns, it is changed to a ready descriptor set;

Read now:

1. The data in the socket receiving buffer is greater than or equal to the so_rcvlowat mark size;

2. Receive the TCP connection of Fin; read returns 0;

3. If it is a listener socket, the number of completed Connections cannot be 0;

4. the socket has an error to be processed; read returns-1, and the error code is obtained and cleared through errno or so_error socket options.

Prepare for writing:

1. The available space in the socket sending buffer is greater than or equal to the so_sndlowat mark size;

2. Write of the connection is disabled, and write will generateSigpipeSignal;

3. The non-blocking connect socket has been established or failed;

4. the socket has an error to be processed; write returns-1, and the error code is obtained and cleared through errno or so_error socket options.

Note:

So_rcvlowat for TCP and UDP, the default value is 1;

For TCP and UDP, the default value of sndlowat is 2048;

The integer returned by getsockopt is the socket to be processed error. so_error is then reset from kernel to 0;

Refer:

UNIX Network programmingvolume 1, third edition: thesockets networking API

Network Programming socket-Overview of TCP select