struct sigaction
{void (*sa_handler) (int);sigset_t sa_mask;int sa_flags;void (*sa_restorer) (void);}

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string.h>
#include <unistd.h>
#include <signal.h>
#include <fcntl.h> int listenfd1;void do_sigio(int sig)
{int clifd, clilen;struct sockaddr_in cli_addr;char buffer[256];clifd = accept(listenfd1, (struct sockaddr *) &cli_addr, &clilen);bzero(buffer, 256);read(clifd, buffer, 255);printf("Listenfd1 Message%s\r\n", buffer);
}int main(int argc, char *argv[])
{//绑定监听7779端口的fdstruct sockaddr_in serv_addr1;listenfd1 = socket(AF_INET, SOCK_DGRAM, 0);bzero((char *) &serv_addr1, sizeof(serv_addr1));serv_addr1.sin_family = AF_INET;serv_addr1.sin_port = htons(7779);serv_addr1.sin_addr.s_addr = INADDR_ANY;struct sigaction sigio_action;memset(&sigio_action, 0, sizeof(sigio_action));sigio_action.sa_flags = 0;sigio_action.sa_handler = do_sigio;sigaction(SIGIO, &sigio_action, NULL);fcntl(listenfd1, F_SETOWN, getpid());int flags;flags = fcntl(listenfd1, F_GETFL, 0);flags |= O_ASYNC | O_NONBLOCK;fcntl(listenfd1, F_SETFL, flags);bind(listenfd1, (struct sockaddr *) &serv_addr1, sizeof(serv_addr1));while(1);close(listenfd1);return 0;}

#include <stdio.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <string.h>
#include <unistd.h>int main(int argc, char* argv[])
{int socketfd, n;socketfd = socket(AF_INET, SOCK_DGRAM, 0);struct sockaddr_in serv_addr;bzero((char *)&serv_addr, sizeof(serv_addr));serv_addr.sin_family = AF_INET;serv_addr.sin_port = htons(7779);connect(socketfd,(struct sockaddr *)  &serv_addr, sizeof(serv_addr));write(socketfd, "client message", 14);return 0;}