linux flock使用示例代码

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代码如下：

#include <stdlib.h>

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/stat.h>

int main(int args, char** argv)
{
int n1 = atoi(argv[1]);
int n2 = atoi(argv[2]);
int n3 = atoi(argv[3]);
printf("%d %d lock %d - %d \n", args, n1, n2, n3);

printf("pid [%d] \n", getpid());

int fd = open("1.log", O_RDWR|O_CREAT, S_IRUSR|S_IWUSR);
if(fd == -1)
        printf("open error %d", errno);
struct flock flk;
flk.l_type = n1 == 1 ? F_WRLCK : F_RDLCK;
flk.l_whence = SEEK_SET;
flk.l_start = n2;
flk.l_len = n3;
int nRet = fcntl(fd, F_SETLK, &flk);
printf("fcntl lock ret:%d \n", nRet);
if(nRet == -1)
{
flk.l_type = F_RDLCK;
flk.l_whence = SEEK_SET;
flk.l_start = n2;
flk.l_len = n3;
nRet = fcntl(fd, F_GETLK, &flk);
printf("type F_WRLCK[%d] F_RDLCK[%d] F_UNLCK[%d]\n", F_WRLCK, F_RDLCK, F_UNLCK);
printf("whence SEEK_SET[%d] SEEK_CUR[%d] SEEK_END[%d] \n", SEEK_SET, SEEK_CUR , SEEK_END);
printf("ret[%d]    current lock pid[%d] type[%d] whence[%d] start[%d] len[%d] \n", nRet, flk.l_pid, flk.l_type, flk.l_whence, flk.l_start, flk.l_len);

struct stat buf;
nRet = stat("1.log", &buf);
printf("stat ret:%d   fileSize:%d \n", nRet, buf.st_size);
}
sleep(10);
return 0;
}

3个参数，参数1：1 是写锁，0是读锁；参数2：起始字节索引；参数3：待锁字节长度

./a.out 1 0 10

./a.out 0 2 4

如果锁失败，会获取当前锁的信息并打印；

如果锁了10字节，解锁中间的一个字节，会被分割变成2个锁

详见 unix环境高级编程14.2节

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