p10-4.c

SUN Solaris8平台下进程间通信

#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>
#include "filelock.h"
#include "err_exit.h"
const char *test_file = "/usr/local/games/score.dat ";
struct userid {
    char *user_name;
    int index;
    int score;
};
/* 读出并输出游戏得分记录 */
void read_score(int fd, struct userid *user) 
{
    off_t offset;
    int len;
    struct userid user_record,comm_record;
    int record_len = sizeof(struct userid);
    /* 读取霸主得分，霸主得分记录位于文件的开始。首先置等待读锁 */
    if (READW_LOCK(fd,0,SEEK_SET, record_len) == -1)    
       err_exit("READ_LOCK error");
    lseek(fd, 0L,SEEK_SET);
    read(fd, &comm_record, record_len);
    /* 释放读锁 */
    if (UN_LOCK(fd, 0L,SEEK_SET, record_len) == -1) 
        printf("Process %d - failed to unlock region\n");
    /* 读取用户得分，用户得分记录在文件中的位置根据user的index算出 */
    offset = user_record.index * record_len;
    lseek(fd, offset,SEEK_SET);
    read(fd, &user_record, record_len);
    /* 输出得分记录 */
    scores_report(&comm_record, &user_record);
    return;
}
void record_score(int fd, struct userid *user, int value)
{
    off_t offset;
    struct userid user_record,comm_record;
    int record_len = sizeof(struct userid);
    /* 确定用户得分记录在文件中的位置并读用户得分记录 */
    offset = user->index * record_len;
    lseek(fd, offset,SEEK_SET);
    read(fd, &user_record, record_len);
    /* 若用户当前得分高于历史最高分，更新历史最高分；若还高于霸主得分，更改霸主记录 */
    if (user_record.score < value ){ 
        /* 更改历史最高分 */
       user_record.score = value;       
       write(fd, &user_record, record_len);  
        /* 读取霸主得分，为此，首先设置等待写锁。，霸主得分记录位于文件的开始. */
       if (WRITEW_LOCK(fd,0,SEEK_SET, record_len) == -1)    
          err_exit("WRITEW_LOCK error");
       lseek(fd, 0L, SEEK_SET);
       read(fd, &comm_record, record_len);
        /* 若新霸主诞生，更改霸主记录 */
       if (comm_record.score < value){ 
           comm_record.score = value;
           comm_record.user_name = user->user_name;
           lseek(fd, 0L, SEEK_SET);
           write(fd, &comm_record, record_len);
        }
        /* 释放写锁 */    
        if (UN_LOCK(fd, 0L,SEEK_SET, record_len) == -1) 
           err_exit("UN_LOCK error");
    }
    return;
}