deadlock.c

unix环境高级编程的源代码

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

static void lockabyte(const char *, int, off_t);

int
main(void)
{
    int        fd;
    pid_t    pid;

        /* Create a file and write two bytes to it */
    if ( (fd = creat("templock", FILE_MODE)) < 0)
        err_sys("creat error");
    if (write(fd, "ab", 2) != 2)
        err_sys("write error");

    TELL_WAIT();
    if ( (pid = fork()) < 0)
        err_sys("fork error");

    else if (pid == 0) {            /* child */
        lockabyte("child", fd, 0);
        TELL_PARENT(getppid());
        WAIT_PARENT();
        lockabyte("child", fd, 1);

    } else {                        /* parent */
        lockabyte("parent", fd, 1);
        TELL_CHILD(pid);
        WAIT_CHILD();
        lockabyte("parent", fd, 0);
    }
    exit(0);
}

static void
lockabyte(const char *name, int fd, off_t offset)
{
    if (writew_lock(fd, offset, SEEK_SET, 1) < 0)
        err_sys("%s: writew_lock error", name);

    printf("%s: got the lock, byte %d\n", name, offset);
}