linux网络编程:设置非阻塞socket收发数据

    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);
	}
}

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