非阻塞式I/O包括非阻塞输入操作,非阻塞输出操作,非阻塞接收外来连接,非阻塞发起外出连接。包括的函数有:read, readv, recv, recvfrom, recvmsg, write, writev, send, sendto, sendmsg, accept。
将socket 设置为非阻塞模式有三总方法:
(1)创建socket的时候,指定socket是异步的,在type的参数中设置SOCK_NONBLOCK标志即可。
int socket(int domain, int type, int protocol);
int s = socket(AF_INET, SOCK_STREAM | SOCK_NONBLOCK, IPPROTO_TCP);
(2)使用fcntl函数:
fcntl(sockfd, F_SETFL, fcntl(sockfd, F_GETFL, 0) | O_NONBLOCK);
(3)使用ioctl函数:
ioctl(sockfd, FIONBIO, 1); //1:非阻塞 0:阻塞
下面改写 linux网络编程:使用多进程实现socket同时收发数据 中的程序
/*=============================================================================
# FileName: nonblocktcp.c
# Desc: set the connetfd unblock
# Author: licaibiao
# LastChange: 2017-02-14
=============================================================================*/
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#define MAXLINE 256
#define PORT 6666
void process_out(int signo)
{
exit(EXIT_SUCCESS);
}
void write_func(int pid, int fd)
{
char* write = "I am server";
printf("write id = %d\n",pid);
signal(SIGUSR1,process_out);
while(1)
{
sleep(1);
send(fd,write,strlen(write)+1,0);
}
}
void read_func(int pid, int fd)
{
char readbuff[MAXLINE];
int n = 0;
printf("read id = %d \n",pid);
memset(&readbuff,0,sizeof(readbuff));
while(1)
{
n = recv(fd, readbuff, MAXLINE, 0);
if(n > 0)
{
printf("server recv data: %s \n",readbuff);
}
else if(n == 0)
{
break;
}
sleep(1);
//printf("===\n");
};
printf("exit read function\n");
kill(pid, SIGUSR1);
exit(EXIT_SUCCESS);
}
int main(void)
{
int listenfd,connetfd;
int on = 1;
int addrlen = 0;
int flags;
pid_t pid, pid_child, pid_send;
struct sockaddr_in server_addr;
struct sockaddr_in client_addr;
if ((listenfd = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0)
{
printf("create socket err \n");
}
addrlen = sizeof(struct sockaddr_in);
memset(&server_addr, 0, addrlen);
server_addr.sin_family = AF_INET;
server_addr.sin_addr.s_addr = htonl(INADDR_ANY);
server_addr.sin_port = htons(PORT);
if (setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0)
{
printf("bind socket error: %s(errno: %d)\n",strerror(errno),errno);
exit(0);
}
if( bind(listenfd, (struct sockaddr*)&server_addr, sizeof(server_addr)) == -1)
{
printf("bind socket error: %s(errno: %d)\n",strerror(errno),errno);
exit(0);
}
if( listen(listenfd, 10) == -1)
{
printf("listen socket error: %s(errno: %d)\n",strerror(errno),errno);
exit(0);
}
printf("wait client accpt \n");
while(1)
{
if( (connetfd = accept(listenfd, (struct sockaddr*)&client_addr, &addrlen)) == -1)
{
printf("accept socket error: %s(errno: %d)",strerror(errno),errno);
continue;
}
/* set NONBLOCK */
flags = fcntl(connetfd, F_GETFL, 0);
fcntl(connetfd, F_SETFL, flags | O_NONBLOCK);
signal(SIGCHLD, SIG_IGN);
pid = fork();
if(pid == -1)
{
printf("fork err \n");
}
if(pid == 0)
{
pid_child = fork();
if(pid_child == 0)
{
pid_send = getpid();
read_func(pid_send, connetfd);
}
else
{
pid_send = getpid();
write_func(pid_send,connetfd);
}
}
}
}
在该程序中,当接收到客户端的一个连接后,将连接描述符设置成非阻塞的:
flags = fcntl(connetfd, F_GETFL, 0);
fcntl(connetfd, F_SETFL, flags | O_NONBLOCK);
这样设置之后,在读和写函数中的send和recv函数都变为了非阻塞模式。在这里我们使用的是sleep来做一个延时循环检测数据可读和数据可发送。在这里常用的套接字超时并不是sleep函数。我们可以使用下面的三种套接字超时方法。
套接字超时:
(1)调用alarm,它在指定超时期满时产生SIGALARM信号,这与linux信号处理类似。
static void sig_alrm(int signo)
{
return; /* just interrupt the recvfrom() */
}
void dg_cli(FILE *fp, int sockfd, const SA *pservaddr, socklen_t servlen)
{
int n;
char sendline[MAXLINE], recvline[MAXLINE + 1];
signal(SIGALRM, sig_alrm);
while (Fgets(sendline, MAXLINE, fp) != NULL) {
sendto(sockfd, sendline, strlen(sendline), 0, pservaddr, servlen);
alarm(5);
if ( (n = recvfrom(sockfd, recvline, MAXLINE, 0, NULL, NULL)) < 0) {
if (errno == EINTR)
fprintf(stderr, "socket timeout\n");
else
err_sys("recvfrom error");
} else {
alarm(0);
recvline[n] = 0; /* null terminate */
fputs(recvline, stdout);
}
}
}
(2)在select 中阻塞等待I/O(select 有内置的时间限制),以此代替直接阻塞在read或write调用上。
int readable_select(int fd, int sec)
{
fd_set rset;
struct timeval tv;
FD_ZERO(&rset);
FD_SET(fd, &rset);
tv.tv_sec = sec;
tv.tv_usec = 0;
return(select(fd+1, &rset, NULL, NULL, &tv));
/* 4> 0 if descriptor is readable */
}
(3)使用较新的SO_RCVTIMEO和SO_SNDTIMEO套接字选项。
void dg_cli(FILE *fp, int sockfd, const SA *pservaddr, socklen_t servlen)
{
int n;
char sendline[MAXLINE], recvline[MAXLINE + 1];
struct timeval tv;
tv.tv_sec = 5;
tv.tv_usec = 0;
setsockopt(sockfd, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv));
while (fgets(sendline, MAXLINE, fp) != NULL) {
sendto(sockfd, sendline, strlen(sendline), 0, pservaddr, servlen);
n = recvfrom(sockfd, recvline, MAXLINE, 0, NULL, NULL);
if (n < 0) {
if (errno == EWOULDBLOCK) {
fprintf(stderr, "socket timeout\n");
continue;
} else
err_sys("recvfrom error");
}
recvline[n] = 0; /* null terminate */
fputs(recvline, stdout);
}
}