lockf( fd, mode, size );

mode 为 1 时表示加锁，为 0 时表示解锁。

#include
     
      #include
      
       #include
       
        #include
        
         #include
         
          int main(){    pid_t pid;    int retval;    char buf[6] = "hello";    if( (pid = fork() )< 0 )    {        printf("fork error\n");        exit(-1);    }    else if( pid == 0 )    {        while(1)        {            if( lockf(1,1,0) < 0 )            {                printf("lockf on error\n");                exit(-1);            }            sleep(1);            printf("this is in child!\n");            sleep(1);            printf("this is in child!\n");            if( lockf(1,0,0) <0 )            {                printf("lockf off error\n");                exit(-1);                                }            sleep(1);        }        printf("this is child end\n");        exit(-1);    }    //wait(&retval);    while(1)    {        if( lockf(1,1,0) < 0 )        {            printf("lockf on error\n");            exit(-1);        }        sleep(1);        printf("this is in parent!\n");        sleep(1);        printf("this is in parent!\n");        if( lockf(1,0,0) <0 )        {            printf("lockf off error\n");            exit(-1);                            }        sleep(1);    }    printf("this is parent process end\n");    return 0;}