使用信号SIGALRM 为 recvfrom 设置超时，防止死等待

 1 #include "apue.h"
 2 static void sig_alarm(int);
 3 void do_cli(int sockfd,FILE* fp,(SA*)pserveraddr,socklen_t servlen)
 4 {    
 5     char sendbuf[maxlen],recvbuf[maxlen];
 6     int n;
 7     while((fgets(sendbuf,maxlen,fp))!=NULL)
 8     {    
 9         singal(SIGALRM,sig_alrm);    //register an signal exec function
10         sendto(sockfd,sendbuf,strlen(sendbuf),0,pserveraddr,servlen);
11         alarm(5);
12         if((n=recvfrom(sockfd,recvbuf,maxlen,0,NULL,NULL))<0)
13         {
14             if(errno==EINTR)    //time out
15             {
16                 fprintf(stderr,"time out 5 sec!\n");
17             }
18             else{                //recv error
19                 perror("recv error!\n");
20             }
21         }
22         else
23         {
24             alarm(0);    // turn off alarm . we have successed recv a message;
25             recvbuf[n]='\0';
26             fputs(recvbuf,stdout);
27         }
28     }
29 
30 }
31 static void sig_alarm(int signo)
32 {
33     return;
34 }