lock.c

Linux 下 C 库及常用 系统调用的使用事例

#include <unistd.h>
#include <sys/file.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void lock_set(int fd,int type);
int lock_reg(int fd, int cmd, int type, off_t offset, int whence, off_t len);

int main(int argc, char *argv[])
{
	int fd,nwrite,nread,len, c;
	char reply;
	char buff[100];
	char buf_r[100];
	/*打开文件*/
	fd=open("hello",O_RDWR | O_CREAT, 0666);
	if(fd < 0)
    {
        //printf("open error\n");
        perror("open");
        exit(1);
    }

	/*使用getopt函数获取客户端选项*/
	while ((c = getopt(argc, argv, "w:r")) != -1)
	switch(c)
	{
		/*加上写入锁*/
		case 'w':
			strcpy(buff, optarg);
			lock_set(fd, F_WRLCK);
			len = sizeof(buff);
        		if((nwrite=write(fd,buff,len))>0){
                		printf("write success\n");
			}
			while(1)
			{
				printf("want to unlock?(Y/N)\n");
				scanf("%c",&reply);
				/*给文件上锁*/
				if((reply == 'Y') || (reply == 'y'))
				{
					lock_set(fd, F_UNLCK);
					break;
				}
				else
				{
					sleep(2);
					continue;
				}
			}
			break;
		/*加入读取锁*/
		case 'r':
			lock_set(fd, F_RDLCK);
        		lseek(fd,0,SEEK_SET);
        		if((nread=read(fd,buf_r,100)) > 0){
                		printf("read:%s\n",buf_r);
        		}
			while(1)
			{
				printf("want to unlock?(Y/N)\n");
				scanf("%c",&reply);
				/*给文件上锁*/
				if((reply == 'Y') || (reply == 'y'))
				{
					lock_set(fd, F_UNLCK);
					break;
				}
 				else
				{
					sleep(2);
					continue;
				}
			}
			break;
		default:
			printf("prog [-w+content] [-r]\n");
			break;
	}
	close(fd);
	exit(0);
}

/*测试锁例子*/
lock_test(int fd, int type, off_t offset, int whence, off_t len)
{
	struct flock lock;
	lock.l_type = type; /*可以为F_RDLCK或者F_WRLCK*/
	lock.l_start = offset;
	lock.l_whence = whence;
	lock.l_len = len;
	if(fcntl(fd, F_GETLK, &lock) < 0)
		perror("fcntl");
	if(lock.l_type == F_UNLCK)
		return(0);
	return(lock.l_pid);
}
/*给文件加锁解锁例子*/
int lock_reg(int fd, int cmd, int type, off_t offset, int whence, off_t len)
{
	struct flock lock;
	lock.l_type = type; /*F_RDLCK, F_WRICK, F_UNLCK*/
	lock.l_start = offset;
	lock.l_whence = whence;
	lock.l_len = len;
	return(fcntl(fd, cmd, &lock));
}


/* 加锁函数 */
void lock_set(int fd, int type)
{
    struct flock lock;
    lock.l_whence = SEEK_SET;
    lock.l_start = 0;
    lock.l_len = 0;
    while(1)
    {
        lock.l_type = type;

        if(fcntl(fd, F_SETLK, &lock) == 0)
        {
            if(lock.l_type == F_RDLCK)
            {
                printf("read lock set by %d\n", getpid());
            } 
            else if(lock.l_type == F_WRLCK)
            {
                printf("write lock set by %d\n", getpid());
            }
            else if(lock.l_type == F_UNLCK)
            {
                printf("release lock by %d\n", getpid());
            }

            return;
            
        }

        fcntl(fd, F_GETLK, &lock);

        if(lock.l_type != F_UNLCK)
        {
            if(lock.l_type != F_UNLCK)
            {
                if(lock.l_type == F_RDLCK)
                {
                    printf("read lock already set by %d\n", lock.l_pid);
                }
            }
            else if(lock.l_type == F_WRLCK)
            {
                printf("write lock already set by %d\n", lock.l_pid);
            }
        }
    }
}