Select model for I/O model

I have just taken a look at the relevant knowledge of the I/O model and made a summary to share with you.

The selct model refers to the operation in the socket set fd_set (multiple sockets can be connected together to form a socket set)

The socket set is also divided into three forms. The corresponding relationships are as follows:

Socket set Event occurredWhat exactly?

The readfds select function waits for pending connection requests or data reading or connection shutdown/restart/interruption.

The writefds select function waits for a successful connection (call Connect) or data to be writable.

Wait TFDs select function waiting for connection failure or OOB data readable

The following method is used to determine whether to read and write data. For example:

Test whether a socket S is readable and add it to readfds. Wait until the select function returns. After the call is complete, check whether s is still in readfds.

The general process is as follows:

(1) initialize a socket set fdsocket and add the listening socket handle slisten to this set:

Fd_set fdsocket;

Fd_set (slisten, & fdsocket );

(2) When a copy of The fdsockt set fdread is passed to the select function, when an event occurs, the Select function will remove the outstanding socket handle not found in fdread and return:

Fd_set fdread = fdsocket;

Int nret =: Select (0, & fdread, null );

(3) Compare the original fdsocket set with fdread processed by select to determine which sockets have pending I/O and further process them:

For (INT I = 0; I <(INT) fdsocket. fd_count; I ++)
{
If (fd_isset (fdsocket. fd_array [I], & fdread) // you can check whether the object is readable.
{
If (fdsockt. fd_array [I] = slisten) // indicates that the listener socket wants to connect.
{
Sockaddr_in addrremote;
Int naddrlen = sizeof (addrremote );
Socket snew =: accept (slisten, (sockaddr *) & addrremote, & naddrlen );
Fd_set (snew, & fdsockt );
}
Else // indicates that the data is readable.
{
Char sztext [256];
Int nrecv =: Recv (fdsocket. fd_array [I], sztext, strlen (sztext), 0 );
}
}
}

You can know whether it can be written, which is similar to this one.

The advantage of the model selection is that multiple socket requests can be processed in a single thread, but the number of sockets added to the fd_set structure is limited by default. The maximum number of sockets can be up to 1024.

If there are too many sockets, you have to set these 1000 sockets before calling the SELECT statement. After the SELECT statement is returned, check the 1000 sockets on the right.

Finally, I like the following sentence:

Some persistence makes a series of accidents.

Select model for I/O model