c - Reading from FIFO(named pipe) in While loop without body -

im trying make tic tac toe game server-client in c. on server side have read fifo(named pipe) 2 pids. made loop run until read (from fifo) return value different zero(mean client wrote pid fifo).

i have reason, on laptop it's not working , on buddy laptop it's working. same code!! have no clue why happening.

and when add body first while loop , put printf("1"); in it. it's work , pid1 reads pid fifo.

the code of server:

#include <stdio.h> #include <sys/stat.h>  #include <fcntl.h> #include <unistd.h> #include <signal.h> #include <sys/ipc.h> #include <sys/shm.h> #include <string.h>  void main() {     int fd,shmid;     key_t shmkey;     void *shm_add;     pid_t pid,pid1=0,pid2=0;     mkfifo("fifo_clienttoserver",400);     fd=open("fifo_clienttoserver",o_nonblock | o_rdonly);     pid=fork();     if(pid==0)     {         while(read(fd,&pid1,sizeof(pid_t))==0); //(1)      }     else     {         wait();         while(read(fd,&pid2,sizeof(pid_t))==0)         {             if(pid2!=pid1)                 break;         }            remove("fifo_clienttoserver");     }     printf("\nfirst pid= %d\nsecond pid= %d\n",pid1,pid2); } 

the code of client:

#include <stdio.h> #include <sys/stat.h>  #include <fcntl.h> #include <unistd.h> #include <signal.h> #include <stdbool.h>  void my_handler(int signum);  bool over=false; int board[3][3]={{0,0,0},{0,0,0},{0,0,0}}; char tav; static bool first=false;  void main() {     int fd;     pid_t pid1=getpid();     signal(sigusr2, my_handler);     fd=open("fifo_clienttoserver",o_wronly);     write(fd,&pid1,sizeof(pid_t));     printf("%d\n",pid1);     while(!over);  }  void my_handler(int signum) {     char geth;     printf("1");     //check if signal sigusr2.     if (signum == sigusr2)     {     if(!first)     {         tav='x';         printf("x");         first=true;     }     else     {         tav='c';         printf("c");     }     } } 

it's weird , dont know how deal it! when change line (1) while(read(fd,&pid1,sizeof(pid_t))==0){printf("1");} it's working , pid1 value.

please me.

man read:

if process has pipe open writing , o_nonblock set, read() shall return -1 , set errno [eagain].

so, while loop breaks without read.

in event, busy waiting bad. drop o_nonblock or use

    fd_set readfds;     fd_zero(&readfds);     fd_set(fd, &readfds);     select(fd+1, &readfds, null, null, null); 

before read().