devzero.c

unix环境高级编程的源代码

#include    <sys/types.h>
#include    <sys/mman.h>
#include    <fcntl.h>
#include    "ourhdr.h"

#define    NLOOPS        1000
#define    SIZE        sizeof(long)    /* size of shared memory area */

static int    update(long *);

int
main()
{
    int        fd, i, counter;
    pid_t    pid;
    caddr_t    area;

    if ( (fd = open("/dev/zero", O_RDWR)) < 0)
        err_sys("open error");
    if ( (area = mmap(0, SIZE, PROT_READ | PROT_WRITE,
                                      MAP_SHARED, fd, 0)) == (caddr_t) -1)
        err_sys("mmap error");
    close(fd);        /* can close /dev/zero now that it's mapped */

    TELL_WAIT();
    if ( (pid = fork()) < 0) {
        err_sys("fork error");
    } else if (pid > 0) {            /* parent */
        for (i = 0; i < NLOOPS; i += 2) {
            if ( (counter = update((long *) area)) != i)
                err_quit("parent: expected %d, got %d", i, counter);
            TELL_CHILD(pid);
            WAIT_CHILD();
        }

    } else {                        /* child */
        for (i = 1; i < NLOOPS + 1; i += 2) {
            WAIT_PARENT();
            if ( (counter = update((long *) area)) != i)
                err_quit("child: expected %d, got %d", i, counter);
            TELL_PARENT(getppid());
        }
    }
    exit(0);
}
static int
update(long *ptr)
{
    return( (*ptr)++ );    /* return value before increment */
}