linux编程fcntl获取和设置文件锁

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#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; }