svshm/svshm_xfr_writer.c

This is svshm/svshm_xfr_writer.c (Listing 48-2, page 1003), an example from the book, The Linux Programming Interface.

The source code file is copyright 2022, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

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  Cover of The Linux Programming Interface

Function list (Bold in this list means a function is not static)

#include "semun.h"              /* Definition of semun union */
#include "svshm_xfr.h"
int
main(int argc, char *argv[])
{
    int semid, shmid, bytes, xfrs;
    struct shmseg *shmp;
    union semun dummy;

    semid = semget(SEM_KEY, 2, IPC_CREAT | OBJ_PERMS);
    if (semid == -1)
        errExit("semget");

    if (initSemAvailable(semid, WRITE_SEM) == -1)
        errExit("initSemAvailable");
    if (initSemInUse(semid, READ_SEM) == -1)
        errExit("initSemInUse");

    shmid = shmget(SHM_KEY, sizeof(struct shmseg), IPC_CREAT | OBJ_PERMS);
    if (shmid == -1)
        errExit("shmget");

    shmp = shmat(shmid, NULL, 0);
    if (shmp == (void *) -1)
        errExit("shmat");

    /* Transfer blocks of data from stdin to shared memory */

    for (xfrs = 0, bytes = 0; ; xfrs++, bytes += shmp->cnt) {
        if (reserveSem(semid, WRITE_SEM) == -1)         /* Wait for our turn */
            errExit("reserveSem");

        shmp->cnt = read(STDIN_FILENO, shmp->buf, BUF_SIZE);
        if (shmp->cnt == -1)
            errExit("read");

        if (releaseSem(semid, READ_SEM) == -1)          /* Give reader a turn */
            errExit("releaseSem");

        /* Have we reached EOF? We test this after giving the reader
           a turn so that it can see the 0 value in shmp->cnt. */

        if (shmp->cnt == 0)
            break;
    }

    /* Wait until reader has let us have one more turn. We then know
       reader has finished, and so we can delete the IPC objects. */

    if (reserveSem(semid, WRITE_SEM) == -1)
        errExit("reserveSem");

    if (semctl(semid, 0, IPC_RMID, dummy) == -1)
        errExit("semctl");
    if (shmdt(shmp) == -1)
        errExit("shmdt");
    if (shmctl(shmid, IPC_RMID, 0) == -1)
        errExit("shmctl");

    fprintf(stderr, "Sent %d bytes (%d xfrs)\n", bytes, xfrs);
    exit(EXIT_SUCCESS);
}

 

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