This is my lab report on 11/04/96:


    1  Example of using shared memory:


       #include <stdio.h>
       #include <sys/types.h>
       #include <sys/ipc.h>
       #include <sys/shm.h>

       #define SHM_MODE  (SHM_R|SHM_W)


       int main(void)  {

              int shmid;
              char *shmptr;
              int *p, *q;
              pid_t pid;

              shmid = shmget(IPC_PRIVATE, sizeof(int), SHM_MODE);

              pid = fork();

              if ( pid == 0)  {  // CHILD PROCESS

                    shmptr = (char *)shmat (shmid, 0 , 0);
                    p = (int *)shmptr;

           // READ AN INTEGER TO p, p IS IN SHARED MEMORY.

                    printf("Enter an integer:");
                    scanf("%d", p);

                    shmctl(shmid, IPC_RMID, 0);

                    exit(0);
                               }

                 else  // PARENT PROCESS
                      {

                    shmptr = (char *)shmat (shmid, 0, 0);

             //LET q POINTS TO THE SAME ADDRESS.

                    q = (int *)shmptr;

                    wait();

                    printf("The number was %d\n", *q);

                    shmctl ( shmid, IPC_RMID, 0);

                    exit(0);
                     }

         }


     Non blocking terminal IO:

       We need to read from the terminal in a non blocking way. 

        Example:

           #include <stdio.h>
           #include <fcntl.h>
           
           #define LINESIZE 128

           void menu (void);

           main ()
           {
              char line[LINESIZE];
              int size;
              int fd;

              menu();
              
              fd = open("/dev/tty, O_RDONLY | O_NONBLOCK, "r");

              for ( ; ; )  {
                   
                    sleep(1);
                    size = read(fd, line, 1);
                   
                    if (size > 0)  
                        if (line[0] == '1')  // INPUT IS '1'
                                  {
                             while ((size = read(fd, line, 1)) >0) ;

                             printf("Your choice is 1.\n");
                             menu();
                                    }
                           else {
                             printf("Your choice is 2.\n");
                             break;
                                 }
                        else 
                          printf("Spinning\n");  
                       }
                 }

           void menu(void) {
                  printf("1. Print Statistics.\n");
                  printf("2. Terminate.\n");
                  printf("Enter choice [1|2] > \n");
                }