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# 1  
Old 11-07-2010
semaphores

I am having problem with semaphores. I am trying to protect line where process prints so that every process with print in proper order.This is the code..
Code:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <sys/types.h>

union semun {
  int val;
  struct semid_ds *buf;
  unsigned short int *array;
  struct seminfo *_buff;
};

int init (int id ){

 union semun mySemun;
 unsigned short val[1];
 val[0] = 1;
 mySemun.array = val;
 int i;
 i = semctl(id , 0 , SETALL,mySemun);

}

int create (key_t  k , int sem_flag){

  int sid;
  sid = semget(k , 1 , 0600 | sem_flag);
  return sid;

}


int semWait(int id){

 struct sembuf op [1];
 op[0].sem_num = 0 ;
 op[0].sem_op = -1;
 op[0].sem_flg = 0;
 int i = semop(id,op,1);
}

int semSig (int id){

 struct sembuf op[1];
 op[0].sem_num = 0;
 op[0].sem_op  = 1;
 op[0].sem_flg = 0;
 int i = semop(id,op,1);

}

int main (int argc, char *argv[]) {

   pid_t childpid = 0;
   int i, n;
   key_t key = ftok(".",'x');
   int mySem;
   mySem  =  create(key,IPC_CREAT);
   init(mySem);
   int m =semctl(mySem,0,GETVAL,0);

  for (i = 1; i < n; i++)
      if (childpid = fork())
         break;


   semWait(mySem);
   printf("Each process will print something here in proper order");
   semSig(mySem);
  
   return 0;
}

I would like first process to print something then second and so on. But i am getting all process mixed up and not in proper order.I am getting something like this...
Code:
myShell$  ./a.out
proccess1  .........
proccess2  .........
myShell$ proccess3  ........
process4 ...........

Can anyone point me in what i am doing wrong.I think output should print...
Code:
process1
process2
process3
process4

# 2  
Old 11-07-2010
Both of those look in the right order to me. process1, process2, process3, process4. But then, that was never what your program was supposed to be printing. What actually happens?
# 3  
Old 11-07-2010
semaphore

each process should print its process id ,parent id and child id...i just wanted to check if my semaphores are ok....thats all
# 4  
Old 11-07-2010
You might want ot wait for the children after all of them are created. and you might want to fflush() immediately after you print. other than that it looks ok.
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