Question

我正在尝试选择呼叫的客户端服务器代码。但是一旦我从客户端发送到服务器，服务器不断从客户端发送的缓冲区中读取，即使客户端在Ist包之后没有发送任何内容。我在哪里做错了？

以下是代码片段：

fd_set readSet,master_list_read;
FD_ZERO(&master_list_read);
FD_SET(STDIN, &master_list_read);//stdin manually trigger reading
FD_SET(sockfd, &master_list_read);//tcp socket

struct timeval tv;
int retval;
tv.tv_sec = 10;
tv.tv_usec = 0;
while(1)
{ 
bool idle=false;
char *buffer=NULL;
int n;

tv.tv_sec = 10;
readSet=master_list_read;
retval = select(sockfd+1, &readSet, NULL, NULL,&tv);
if (retval == -1) 
{
    perror("Error in select\n");
    exit(4);
}
else if(retval==0)
{ 
    printf("*********SEND SUCCESSFUL******\n");
}       
else 
{   
if(FD_ISSET(0, &readSet))
{
    bzero(buf,256);
    fgets(buf,256,stdin); 
    if (send(sockfd, buffer,n, 0) == -1) perror("error in sending MSG to server\n");
}

else  if (FD_ISSET(sockfd, &readSet))  // receives data from server,print it on StdOutput
{  
    bzero(buf,256);
    int nbytes = recv(sockfd, buf, 256,0);
    if(nbytes<=0)
    {
        perror("recv error from server \n");
        exit(0);
    }
}

} //END OF ELSE 
} //end of while
close(sockfd);          
return 0;

Answer 1

select()循环中的while(1)调用会使readSet保持不变。这意味着稍后FD_ISSET（）检查成功。

解决方案很简单：在每次迭代时清除fd_set：

FD_ZERO(&master_list_read);
FD_SET(STDIN, &master_list_read);
FD_SET(sockfd, &master_list_read);
// only now the select() returns what you need
retval = select(sockfd+1, &master_list_read, NULL, NULL,&tv);

// use the master_list_read later

简单地复制fd_set并不能解决问题。

服务器卡在客户端缓冲区中连续选择和读取

1 个答案: