One 、IO Multiplexing

IO Multiplexing is IO Blocked state , Do something else

Two 、select

Realization function ： monitor ; Can listen to many file descriptors
Prototype ：int select(int maxfd, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, const struct timeval *timeout)
fd_set： File descriptor set , A container , It can save a lot of data （ File descriptor ） Array of
maxfd： Range of file descriptors , Larger than the maximum file descriptor to be checked 1
readfds： Read monitored file descriptor set
writefds： The set of file descriptors that are written to monitor
exceptfds： Set of file descriptors monitored by exceptions
timeval： System defined time

Return value , The number of changes returned successfully 、 Failure to return -1
Generally used to monitor reading

#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <unistd.h>
#include <sys/types.h>
#include <fcntl.h>
#include <sys/stat.h>


int main(int argc, char const *argv[])
{
    
    struct timeval time;
    fd_set r_set;
    fd_set all_set;
    time.tv_sec = 3;
    time.tv_usec = 0;
    
    int fd;
    if((fd = open("/dev/input/mouse0", O_RDWR | O_CREAT, 0655)) < 0)
    {
    
        perror("open file error!");
        exit(1);
    }
    FD_SET(fd, &r_set);
    FD_SET(0, &r_set);

    all_set = r_set; // Temporary deposit all_set
    while (1)
    {
    
        r_set = all_set;  // Set every time , Otherwise, the one who will only monitor the change every time 
        int ret = select(fd + 1, &r_set, NULL, NULL, NULL );

        if (FD_ISSET(fd, &r_set) > 0)
        {
    
            int cor;

            read(fd, &cor, sizeof(cor));

            printf("cor = %d\n", cor);
        }

        if (FD_ISSET(0, &r_set) > 0)
        {
    
            char buffer[1024];

            read(0, buffer, sizeof(buffer));

            printf("buffer = %s\n", buffer);
        }
        
    }

    return 0;
}

attach 、 Some additions

fd_set……

timeval

int select(int maxfd, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, const struct timeval *timeout)

( Baidu explains )
Parameter one ： Maximum file descriptor plus 1.
Parameter two ： Used to check readability ,
Parameter 3 ： Used to check Writeability ,
Parameter 4 ： Used to check out of band data ,
Parameter 5 ： A pointer to a timeval Pointer to structure , Used to decide select wait for I/o The longest time , When you're done, come straight back . If it is empty, it will wait （NULL）.
timeval Definition of structure ：

struct timeval
{
    
	long tv_sec; // seconds second 
	long tv_usec; // microseconds millisecond 
}