linux编程fcntl获取和设置文件锁

#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,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,&lock ) == -1 ) {
                        printf( "释放锁失败n" );
                }else{
                        printf( "释放锁成功n" );
                }
        }

        return 0;
}