#include <stdio.h>

#include <stdlib.h>

#include <unistd.h>

#include <sys/types.h>

#include <sys/stat.h>

#include <fcntl.h>

#include <string.h>

#define ERR_EXIT( m ) \

        do \

        { \

                perror( m ); \

                exit( EXIT_FAILURE ); \

        }while( 0 )

int main( int argc, char* argv[] ) {

        if( argc != 2 ) {

                fprintf( stderr, "usage:%s filename", argv[0] );

                exit( EXIT_FAILURE );

        }

        int fd;

        fd = open( argv[1], O_RDWR | O_TRUNC | O_CREAT, 0666 );

        if( -1 == fd ) {

                ERR_EXIT( "文件打开失败" );

        }

        struct flock lock;

        memset( &lock, 0, sizeof( lock ) );

        lock.l_type = F_WRLCK; //写锁

        lock.l_whence = SEEK_SET;

        lock.l_start = 0;

        lock.l_len = 0;

        //加文件写锁, 另一个进程操作文件 直接报错

        //int ret = fcntl( fd, F_SETLK, &lock );

        //加文件写锁, 另一个进程操作文件 会等待这个进程释放锁

        int ret = fcntl( fd, F_SETLKW, &lock );

        if( -1 == ret ) {

                ERR_EXIT( "加锁失败" );

        }else {

                printf( "加锁成功\n" );

                printf( "输入任意字符解锁\n" );

                getchar();

                lock.l_type = F_UNLCK;

                if ( fcntl( fd, F_SETLK, &lock ) == -1 ) {

                        printf( "释放锁失败\n" );

                }else{

                        printf( "释放锁成功\n" );

                }

        }

        return 0;

}