プログラムのソース: pshm_ucase.h

The following header file is included by both programs below. Its primary purpose is to define a structure that will be imposed on the memory object that is shared between the two programs.

#include <sys/mman.h>
#include <fcntl.h>
#include <semaphore.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \
                        } while (0)
#define BUF_SIZE 1024   /* Maximum size for exchanged string */
/* Define a structure that will be imposed on the shared
   memory object */
struct shmbuf {
    sem_t  sem1;            /* POSIX unnamed semaphore */
    sem_t  sem2;            /* POSIX unnamed semaphore */
    size_t cnt;             /* Number of bytes used in 'buf' */
    char   buf[BUF_SIZE];   /* Data being transferred */
};

プログラムのソース: pshm_ucase_bounce.c

The "bounce" program creates a new shared memory object with the name given in its command-line argument and sizes the object to match the size of the shmbuf structure defined in the header file. It then maps the object into the process's address space, and initializes two POSIX semaphores inside the object to 0.

After the "send" program has posted the first of the semaphores, the "bounce" program upper cases the data that has been placed in the memory by the "send" program and then posts the second semaphore to tell the "send" program that it may now access the shared memory.

/* pshm_ucase_bounce.c
   Licensed under GNU General Public License v2 or later.
*/
#include <ctype.h>
#include "pshm_ucase.h"
int
main(int argc, char *argv[])
{
    if (argc != 2) {
        fprintf(stderr, "Usage: %s /shm-path\n", argv[0]);
        exit(EXIT_FAILURE);
    }
    char *shmpath = argv[1];
    /* Create shared memory object and set its size to the size
       of our structure */
    int fd = shm_open(shmpath, O_CREAT | O_EXCL | O_RDWR,
                      S_IRUSR | S_IWUSR);
    if (fd == -1)
        errExit("shm_open");
    if (ftruncate(fd, sizeof(struct shmbuf)) == -1)
        errExit("ftruncate");
    /* Map the object into the caller's address space */
    struct shmbuf *shmp = mmap(NULL, sizeof(*shmp),
                               PROT_READ | PROT_WRITE,
                               MAP_SHARED, fd, 0);
    if (shmp == MAP_FAILED)
        errExit("mmap");
    /* Initialize semaphores as process-shared, with value 0 */
    if (sem_init(&shmp->sem1, 1, 0) == -1)
        errExit("sem_init-sem1");
    if (sem_init(&shmp->sem2, 1, 0) == -1)
        errExit("sem_init-sem2");
    /* Wait for 'sem1' to be posted by peer before touching
       shared memory */
    if (sem_wait(&shmp->sem1) == -1)
        errExit("sem_wait");
    /* Convert data in shared memory into upper case */
    for (int j = 0; j < shmp->cnt; j++)
        shmp->buf[j] = toupper((unsigned char) shmp->buf[j]);
    /* Post 'sem2' to tell the to tell peer that it can now
       access the modified data in shared memory */
    if (sem_post(&shmp->sem2) == -1)
        errExit("sem_post");
    /* Unlink the shared memory object. Even if the peer process
       is still using the object, this is okay. The object will
       be removed only after all open references are closed. */
    shm_unlink(shmpath);
    exit(EXIT_SUCCESS);
}

プログラムのソース: pshm_ucase_send.c

The "send" program takes two command-line arguments: the pathname of a shared memory object previously created by the "bounce" program and a string that is to be copied into that object.

The program opens the shared memory object and maps the object into its address space. It then copies the data specified in its second argument into the shared memory, and posts the first semaphore, which tells the "bounce" program that it can now access that data. After the "bounce" program posts the second semaphore, the "send" program prints the contents of the shared memory on standard output.

/* pshm_ucase_send.c
   Licensed under GNU General Public License v2 or later.
*/
#include <string.h>
#include "pshm_ucase.h"
int
main(int argc, char *argv[])
{
    if (argc != 3) {
        fprintf(stderr, "Usage: %s /shm-path string\n", argv[0]);
        exit(EXIT_FAILURE);
    }
    char *shmpath = argv[1];
    char *string = argv[2];
    size_t len = strlen(string);
    if (len > BUF_SIZE) {
        fprintf(stderr, "String is too long\n");
        exit(EXIT_FAILURE);
    }
    /* Open the existing shared memory object and map it
       into the caller's address space */
    int fd = shm_open(shmpath, O_RDWR, 0);
    if (fd == -1)
        errExit("shm_open");
    struct shmbuf *shmp = mmap(NULL, sizeof(*shmp),
                               PROT_READ | PROT_WRITE,
                               MAP_SHARED, fd, 0);
    if (shmp == MAP_FAILED)
        errExit("mmap");
    /* Copy data into the shared memory object */
    shmp->cnt = len;
    memcpy(&shmp->buf, string, len);
    /* Tell peer that it can now access shared memory */
    if (sem_post(&shmp->sem1) == -1)
        errExit("sem_post");
    /* Wait until peer says that it has finished accessing
       the shared memory */
    if (sem_wait(&shmp->sem2) == -1)
        errExit("sem_wait");
    /* Write modified data in shared memory to standard output */
    write(STDOUT_FILENO, &shmp->buf, len);
    write(STDOUT_FILENO, "\n", 1);
    exit(EXIT_SUCCESS);
}