Chapter 14__高级IO

struct flock {
    short     l_type;         /* F_RDLCK, F_WRLCK, or F_UNLCK */
    short     l_whence;       /* SEEK_SET, SEEK_CUR, SEEK_END */
    OFF_T     l_start;        /* starting offset relative to l_whence */
    OFF_T     l_len;          /* len == 0 means "until end of file" */
    pid_t     l_pid;          /* Process ID of the process holding the lock, 
    　                           returned with F_GETLK */
};

关于struct flock，锁的范围是这么算的
(l_whence + l_start) ~ (l_whence + l_start + l_len)
//  不同的系统，对定义的flock结构，可能不同。 

#include <stdio.h>
#include <fcntl.h>
#include <sys/file.h>
#include <stdlib.h>
#include <unistd.h>

void printLockName(int lockType)
{
    printf("lock type = %d\n", lockType);
    switch (lockType)
    {
        case F_RDLCK : printf("lock type is F_RDLCK\n"); break;
        case F_WRLCK : printf("lock type is F_WRLCK\n"); break;
        case F_UNLCK : printf("lock type is F_UNLCK\n"); break;
        default : printf("not lock type !\n"); 
    }
}

void setFlock(struct flock *lock, int type, off_t offset, int whence, off_t len)
{
    lock->l_type = type;
    lock->l_start = offset;
    lock->l_whence = whence;
    lock->l_len = len;
}

int lock_reg(int fd, int cmd, int type, off_t offset, int whence, off_t len)
{
    struct flock lock;
    setFlock(&lock, type, offset, whence, len);
    return (fcntl(fd, cmd, &lock));
}

pid_t lock_test(int fd, int type, off_t offset, int whence, off_t len)
{
    struct flock lock;
    setFlock(&lock, type, offset, whence, len);

    if (fcntl(fd, F_GETLK, &lock) < 0)
        printf("fcntl error");

    printLockName(lock.l_type);
    if (lock.l_type == F_UNLCK)
        return 0;

    return lock.l_pid;
}

void putexit(char *p)
{
    printf("%s\n", p);
    exit(1);
}

#include <stdio.h>
#include <fcntl.h>

int main(int argc, char *argv[])
{
    int fd = open("/home/long/myc/tem.file", O_RDONLY);
    if (fd < 0)
        putexit("open file error!");

    if (lock_reg(fd, F_SETLK, F_RDLCK, 0, SEEK_SET, 0) == 0)
        printf("lock_reg OK\n");

    printf("getpid() = %d\n", getpid());
    sleep(10);
    close(fd);
    return 0;
}

#include <stdio.h>
#include <fcntl.h>

int main(int argc, char *argv[])
{
    int fd = open("/home/long/myc/tem.file", O_WRONLY);
    if (fd < 0)
        putexit("open file error!");

    int pid = -1;
    pid = lock_test(fd, F_WRLCK, 0, SEEK_SET, 0);
    printf("lock pid = %d\n", pid);

    sleep(10);
    char buf[] = "hello\0";
    if(write(fd, buf, sizeof(buf)) < 0)
        perror("wrire error");

    close(fd);
    return 0;
}