文件区域使用fcntl锁定文件，并且测试

最近研究文件区域，稍微总结一下，以后继续补充：

//lock1.c
/*
程序首先创立一个文件，并且以可读的方式打开，然后在文件中添加一些内容，接着
在文件中设置两个区域，第一个区域为10-30字节，应用共享锁；第二个区域为40-50
字节，应用独占锁，然后程序调用fcntl函数来锁定这两个区域，并在关闭文件和退出程序前等待一分钟
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>

const char *test_file = "/tmp/test_lock";

int main()
{
    int file_desc;
    int byte_count;
    char *byte_to_write = "A";
    struct flock region_1;
    struct flock region_2;
    int res;
    file_desc = open(test_file,O_RDWR | O_CREAT,0666);
    if(!file_desc)
    {
        fprintf(stderr,"Unable to open %s for read/write\n",test_file);
        exit(EXIT_FAILURE);
    }
    for(byte_count = 0;byte_count < 100;byte_count++)
    {
        write(file_desc,byte_to_write,1);
    }
    /*将文件10-30字节设为区域1，并在其上设置共享锁*/
    region_1.l_type = F_RDLCK;
    region_1.l_whence = SEEK_SET;
    region_1.l_start = 10;
    region_1.l_len = 20;
    /*将文件40-50字节设为区域2，并在其上设置独占锁*/
    region_2.l_type = F_WRLCK;
    region_2.l_whence = SEEK_SET;
    region_2.l_start = 40;
    region_2.l_len = 10;
    
    printf("Process %d locking file\n",getpid());
    res = fcntl(file_desc,F_SETLK,®ion_1);
    if(res == -1)
    {
        fprintf(stderr,"Failed to lock region 1\n");
    }
    res = fcntl(file_desc,F_SETLK,®ion_2);
    if(res == -1)
    {
        fprintf(stderr,"Failed to lock region 2\n");
    }
    
    sleep(60);
    
    printf("Process %d closing file\n",getpid());
    close(file_desc);
    exit(EXIT_SUCCESS);
    return 0;
}

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//lock2.c

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

const char *test_file = "/tmp/test_lock";
#define SIZE_TO_TRY 5

void show_lock_info(struct flock *to_show);

int main()
{
    int file_desc;
    int res;
    struct flock region_to_test;
    int start_byte;
    
    file_desc = open(test_file,O_RDWR | O_CREAT,0666);
    if(!file_desc)
    {
        fprintf(stderr,"Unable to open %s for read/write",test_file);
        exit(EXIT_FAILURE);
    }
    
    for(start_byte = 0;start_byte < 99;start_byte++)
    {
        region_to_test.l_type = F_WRLCK;
        region_to_test.l_whence = SEEK_SET;
        region_to_test.l_start = start_byte;
        region_to_test.l_len = SIZE_TO_TRY;
        region_to_test.l_pid = -1;
        printf("Testing F_WRLCK on region from %d to %d\n",start_byte,start_byte+SIZE_TO_TRY);
    
		res = fcntl(file_desc,F_GETLK,®ion_to_test);
		if(res == -1)
		{
		    fprintf(stderr,"F_GETLCK falied\n");
		    exit(EXIT_FAILURE);
		}
		
		if(region_to_test.l_pid != -1)
		{
		    printf("Lock would fail.F_GETLK returned.\n");
		    show_lock_info(®ion_to_test);
		}
		else
		{
		    printf("F_WRLCK - LOCK would succeed\n");
		}
		region_to_test.l_type = F_RDLCK;
		region_to_test.l_whence = SEEK_SET;
		region_to_test.l_start = start_byte;
		region_to_test.l_len = SIZE_TO_TRY;
		region_to_test.l_pid = -1;
		printf("Testing F_RDLCK on region from %d to %d\n",start_byte,start_byte+SIZE_TO_TRY);
		res = fcntl(file_desc,F_GETLK,®ion_to_test);
		if(res == -1)
		{
		    fprintf(stderr,"F_GETLCK falied\n");
		    exit(EXIT_FAILURE);
		}
		if(region_to_test.l_pid != -1)
		{
		    printf("Lock would fail.F_GETLK returned.\n");
		    show_lock_info(®ion_to_test);
		}
		else
		{
		    printf("F_RDLCK - LOCK would succeed\n");
		}
	}
	close(file_desc);
	exit(EXIT_SUCCESS);
}

void show_lock_info(struct flock *to_show)
{
    printf("\tl_type %d",to_show->l_type);
    printf("\tl_whence %d",to_show->l_whence);
    printf("\tl_start %d",to_show->l_start);
    printf("\tl_len %d",to_show->l_len);
    printf("\tl_pid %d",to_show->l_pid);
}

为了测试锁，首先运行lock1（后台运行）,然后再运行lock2

$ ./lock1 &

[1] 6321

[anpan@anpan 数据管理]$ Process 6321 locking file

Process 6321 closing file

./lock2

Testing F_WRLCK on region from 0 to 5

F_WRLCK - LOCK would succeed

Testing F_RDLCK on region from 0 to 5

F_RDLCK - LOCK would succeed

Testing F_WRLCK on region from 1 to 6

F_WRLCK - LOCK would succeed

Testing F_RDLCK on region from 1 to 6

F_RDLCK - LOCK would succeed

………………………………

文章结束给大家分享下程序员的一些笑话语录：看到有人回帖“不顶不是中国人”，他的本意是想让帖子沉了。

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文件和区域
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