reader.c

《Linux应用开发技术详解》附书光盘中的例程。

/**********  reader.c  ***********/

#include <sys/types.h>
#include <sys/mman.h>
#include <semaphore.h>
#include <errno.h>
#include <sys/stat.h>
#include <sys/fcntl.h>

char shm_fn[] = "my_shm";
char sem_fn[] = "my_sem";

/**** READER ****/

main(){
  caddr_t shmptr;
  int shmdes, index;
  sem_t *semdes;
  int SHM_SIZE;

  /* Open the shared memory object */
 SHM_SIZE = sysconf(_SC_PAGE_SIZE);

  if ( (shmdes = shm_open(shm_fn, O_RDWR, 0)) == -1 ) {
     perror("shm_open failure");
     exit();
   }

  if((shmptr = mmap(0, SHM_SIZE, PROT_WRITE|PROT_READ, MAP_SHARED,
               shmdes,0)) == (caddr_t) -1){
     perror("mmap failure");
    exit();
  }

 /* Open the Semaphore */

 semdes = sem_open(sem_fn, 0, 0644, 0);

 if(semdes == (void*) -1){
   perror("sem_open failure");
   exit();
 }

 /* Lock the semaphore */

 if(!sem_wait(semdes)){

  /* Access to the shared memory area */

   for(index = 0; index < 100; index++)
        printf("The shared memory shmptr[%d] = %d\n", index,shmptr[index]);

  /* Release the semaphore lock */

   sem_post(semdes);
  }
  munmap(shmptr, SHM_SIZE);

  /* Close the shared memory object */

  close(shmdes);

  /* Close the Semaphore */

  sem_close(semdes);
  sem_unlink(sem_fn);
}