linux之fcntl函数解析
2013-07-30 16:40
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1、写入锁实例：
[lingyun@localhost fcntl]$ cat fcntl_write.c
/*********************************************************************************
* Copyright: (C) 2013 fulinux<fulinux@sina.com>
* All rights reserved.
*
* Filename: fcntl_write.c
* Description: This file
*
* Version: 1.0.0(07/30/2013~)
* Author: fulinux <fulinux@sina.com>
* ChangeLog: 1, Release initial version on "07/30/2013 04:02:42 PM"
*
********************************************************************************/
#include <unistd.h>
#include <sys/file.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>
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_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);
getchar();
}
}
}
int main(void)
{
int fd;
fd = open("hello",O_RDWR | O_CREAT, 0666);
if(fd < 0)
{
perror("open");
exit(1);
}
lock_set(fd, F_WRLCK);
getchar();
lock_set(fd, F_UNLCK);
getchar();
close(fd);
exit(0);
}
[lingyun@localhost fcntl]$
[lingyun@localhost fcntl]$ touch hello
[lingyun@localhost fcntl]$ ls
fcntl_write.c hello
[lingyun@localhost fcntl]$ gcc fcntl_write.c
[lingyun@localhost fcntl]$ ./a.out
write lock set by 2941
release lock by 2941
[lingyun@localhost fcntl]$
在两个终端上同时运行：
第一个：
[lingyun@localhost fcntl]$ ./a.out
write lock set by 2956
第二个：
[lingyun@localhost fcntl]$ ./a.out
write lock already set by 2956
write lock already set by 2956
第一个：
[lingyun@localhost fcntl]$ ./a.out
write lock set by 2956
release lock by 2956
第二个：
[lingyun@localhost fcntl]$ ./a.out
write lock already set by 2956
write lock already set by 2956
write lock set by 2916
release lock by 2916
互斥锁。
2、读取锁实例：
[lingyun@localhost fcntl_2]$ cat fcntl_read.c
/*********************************************************************************
* Copyright: (C) 2013 fulinux<fulinux@sina.com>
* All rights reserved.
*
* Filename: fcntl_write.c
* Description: This file
*
* Version: 1.0.0(07/30/2013~)
* Author: fulinux <fulinux@sina.com>
* ChangeLog: 1, Release initial version on "07/30/2013 04:02:42 PM"
*
********************************************************************************/
#include <unistd.h>
#include <sys/file.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>
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_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);
getchar();
}
}
}
int main(void)
{
int fd;
fd = open("hello",O_RDWR | O_CREAT, 0666);
if(fd < 0)
{
perror("open");
exit(1);
}
lock_set(fd, F_RDLCK);
getchar();
lock_set(fd, F_UNLCK);
getchar();
close(fd);
exit(0);
}
[lingyun@localhost fcntl_2]$
第一个终端：
[lingyun@localhost fcntl_2]$ ./a.out
read lock set by 3158
release lock by 3158
第二个终端：
[lingyun@localhost fcntl_2]$ ./a.out
read lock set by 3147
release lock by 3147
不是排斥的
三、同时测试写入锁和读取锁实例
让上面两个程序打开同一个文件。
第一个终端：
[lingyun@localhost fcntl_2]$ ./a.out
read lock set by 3238
第二个终端：
[lingyun@localhost fcntl_1]$ ./a.out
read lock already set by 3238
可见被读取锁上锁后写入锁无法上锁，反之亦然。
[lingyun@localhost fcntl_3]$ cat fcntl.c
/*********************************************************************************
* Copyright: (C) 2013 fulinux<fulinux@sina.com>
* All rights reserved.
*
* Filename: fcntl.c
* Description: This file
*
* Version: 1.0.0(08/01/2013~)
* Author: fulinux <fulinux@sina.com>
* ChangeLog: 1, Release initial version on "08/01/2013 02:34:00 PM"
*
********************************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
int main(int argc, char *argv[])
{
int val;
if(argc != 2)
{
perror("argc");
exit(0);
}
if((val = fcntl(atoi(argv[1]), F_GETFL, 0)) < 0)
{
switch(val & O_ACCMODE)
{
case O_RDONLY:
printf("read only");
break;
case O_WRONLY:
printf("write only");
break;
case O_RDWR:
printf("read write");
break;
default:
printf("unknown access mode");
break;
}
if(val & O_APPEND)
printf(", append");
if(val & O_NONBLOCK)
printf(", nonblocking");
#if defined(O_SYNC)
if(val & O_SYNC)
printf(", synchronous writes");
#endif
#if ! defined(_POSIX_C_SOURCE) && defined(O_FSYNC)
if(val & O_FSYNC)
printf(", synchronous writes");
#endif
putchar('\n');
exit(0);
}
}
[lingyun@localhost fcntl]$ cat fcntl_write.c
/*********************************************************************************
* Copyright: (C) 2013 fulinux<fulinux@sina.com>
* All rights reserved.
*
* Filename: fcntl_write.c
* Description: This file
*
* Version: 1.0.0(07/30/2013~)
* Author: fulinux <fulinux@sina.com>
* ChangeLog: 1, Release initial version on "07/30/2013 04:02:42 PM"
*
********************************************************************************/
#include <unistd.h>
#include <sys/file.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>
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_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);
getchar();
}
}
}
int main(void)
{
int fd;
fd = open("hello",O_RDWR | O_CREAT, 0666);
if(fd < 0)
{
perror("open");
exit(1);
}
lock_set(fd, F_WRLCK);
getchar();
lock_set(fd, F_UNLCK);
getchar();
close(fd);
exit(0);
}
[lingyun@localhost fcntl]$
[lingyun@localhost fcntl]$ touch hello
[lingyun@localhost fcntl]$ ls
fcntl_write.c hello
[lingyun@localhost fcntl]$ gcc fcntl_write.c
[lingyun@localhost fcntl]$ ./a.out
write lock set by 2941
release lock by 2941
[lingyun@localhost fcntl]$
在两个终端上同时运行：
第一个：
[lingyun@localhost fcntl]$ ./a.out
write lock set by 2956
第二个：
[lingyun@localhost fcntl]$ ./a.out
write lock already set by 2956
write lock already set by 2956
第一个：
[lingyun@localhost fcntl]$ ./a.out
write lock set by 2956
release lock by 2956
第二个：
[lingyun@localhost fcntl]$ ./a.out
write lock already set by 2956
write lock already set by 2956
write lock set by 2916
release lock by 2916
互斥锁。
2、读取锁实例：
[lingyun@localhost fcntl_2]$ cat fcntl_read.c
/*********************************************************************************
* Copyright: (C) 2013 fulinux<fulinux@sina.com>
* All rights reserved.
*
* Filename: fcntl_write.c
* Description: This file
*
* Version: 1.0.0(07/30/2013~)
* Author: fulinux <fulinux@sina.com>
* ChangeLog: 1, Release initial version on "07/30/2013 04:02:42 PM"
*
********************************************************************************/
#include <unistd.h>
#include <sys/file.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>
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_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);
getchar();
}
}
}
int main(void)
{
int fd;
fd = open("hello",O_RDWR | O_CREAT, 0666);
if(fd < 0)
{
perror("open");
exit(1);
}
lock_set(fd, F_RDLCK);
getchar();
lock_set(fd, F_UNLCK);
getchar();
close(fd);
exit(0);
}
[lingyun@localhost fcntl_2]$
第一个终端：
[lingyun@localhost fcntl_2]$ ./a.out
read lock set by 3158
release lock by 3158
第二个终端：
[lingyun@localhost fcntl_2]$ ./a.out
read lock set by 3147
release lock by 3147
不是排斥的
三、同时测试写入锁和读取锁实例
让上面两个程序打开同一个文件。
第一个终端：
[lingyun@localhost fcntl_2]$ ./a.out
read lock set by 3238
第二个终端：
[lingyun@localhost fcntl_1]$ ./a.out
read lock already set by 3238
可见被读取锁上锁后写入锁无法上锁，反之亦然。
[lingyun@localhost fcntl_3]$ cat fcntl.c
/*********************************************************************************
* Copyright: (C) 2013 fulinux<fulinux@sina.com>
* All rights reserved.
*
* Filename: fcntl.c
* Description: This file
*
* Version: 1.0.0(08/01/2013~)
* Author: fulinux <fulinux@sina.com>
* ChangeLog: 1, Release initial version on "08/01/2013 02:34:00 PM"
*
********************************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
int main(int argc, char *argv[])
{
int val;
if(argc != 2)
{
perror("argc");
exit(0);
}
if((val = fcntl(atoi(argv[1]), F_GETFL, 0)) < 0)
{
switch(val & O_ACCMODE)
{
case O_RDONLY:
printf("read only");
break;
case O_WRONLY:
printf("write only");
break;
case O_RDWR:
printf("read write");
break;
default:
printf("unknown access mode");
break;
}
if(val & O_APPEND)
printf(", append");
if(val & O_NONBLOCK)
printf(", nonblocking");
#if defined(O_SYNC)
if(val & O_SYNC)
printf(", synchronous writes");
#endif
#if ! defined(_POSIX_C_SOURCE) && defined(O_FSYNC)
if(val & O_FSYNC)
printf(", synchronous writes");
#endif
putchar('\n');
exit(0);
}
}
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