操作系统实验之八读者优先问题

一、代码实现

读者进程和写者进程如下：
Main.cpp

#include 
#include 
#include 
#include 
#include "buffer.h"
#include "deal.h"
#define MAX 20

struct sto{
    sem_t mutex;
    sem_t wrt;
};
struct sto shared;
int readcount;

void *Read(void *arg)
{
    Instruction *ins = (Instruction*)arg;
    sleep(ins->start);//等待一段时间，开始申请资源

    //有读者请求资源，则读者数目加1
    //判断是否有写者在使用共享数据段，有的话，等待
    sem_wait(&shared.mutex);
    readcount++;
    if(readcount == 1) sem_wait(&shared.wrt);
    sem_post(&shared.mutex);

    //开始读取共享数据段
    cout<<"Reader "<serial_num<<" is reading."<last);
    cout<<"Reader "<serial_num<<" end reading."<//读取完毕后,读者数目减去1。
    //只有全部读者读取完毕后，唤醒写者线程
    sem_wait(&shared.mutex);
    readcount--;
    if(readcount == 0) sem_post(&shared.wrt);
    sem_post(&shared.mutex);

    return(NULL);
}

void *Write(void *arg)
{
    Instruction *ins = (Instruction*)arg;
    sleep(ins->start);

    //写者读取共享数据段
    sem_wait(&shared.wrt);
    cout<<"Writer "<serial_num<<" is writing."<last);
    cout<<"Writer "<serial_num<<" end writing."<shared.wrt);

    return(NULL);
}

int main()
{
    FILE *fp;
    char file[MAX];
    int i;

    pthread_t tid_read;
    pthread_t tid_write;
    Instruction *ins = new Data();
    sem_init(&shared.mutex, 0, 1);
    sem_init(&shared.wrt, 0, 1);
    readcount = 0;

    fp = fopen("test.txt", "r");
    while(fgets(file, MAX, fp)){
        ins = Deal(file);
        if(ins->character == 'R'){
            pthread_create(&tid_read, NULL, Read, (void*)ins);
        }
        else{
            pthread_create(&tid_write, NULL, Write, (void*)ins);
        }
        /*cout<serial_num<<" "<character<<" ";
        cout<start<<" "<last<<" ";
        cout<

    }

    sem_destroy(&shared.mutex);
    sem_destroy(&shared.wrt);

    sleep(50);

    return 0;
}

为了便于测试，完成以下两段辅助代码：
deal.h

#ifndef DEAL_H_
#define DEAL_H_

#include 
#include 
#include 
#include 
#include 
using namespace std;

typedef struct Data{
    Data(){
        serial_num = 0;
        character = ' ';
        start = 0;
        last = 0;
    }

    int serial_num;
    char character;
    int start;
    int last;
} Instruction;

Instruction *Deal(char file[]);

#endif

deal.cpp

#include "deal.h"

Instruction *Deal(char file[]){
    Instruction *ins = new Data();
    int i;
    int j = 0;
    string tmp = "";

    int len = strlen(file);
    for(i = 0; i < len; i++){
        if(file[i] != ' ' && file[i] != '\n')
            tmp += file[i];

        else{
            if(tmp != ""){
                switch(j){
                    case 0: ins->serial_num = atoi(tmp.c_str());
                            tmp = "";
                            break;
                    case 1: ins->character = tmp.at(0);
                            tmp = "";
                            break;
                    case 2: ins->start = atoi(tmp.c_str());
                            tmp = "";
                        break;
                    case 3: ins->last = atoi(tmp.c_str());
                            tmp = "";
                        break;
                }
                j++;
            }
        }
    }
    return ins;
}

二、测试数据及结果

　　测试数据文件包括n行测试数据，分别描述创建的n个线程是读者还是写者，以及读写操作的开始时间和持续时间。每行测试数据包括四个字段，各个字段间用空格分隔。第一字段为一个正整数，表示线程序号。第二字段表示相应线程角色，R表示读者，W表示写者。第三字段为一个正数，表示读写操作的开始时间：线程创建后，延迟相应时间(单位为秒)后发出对共享资源的读写申请。第四字段为一个正数，表示读写操作的持续时间。当线程读写申请成功后，开始对共享资源的读写操作，该操作持续相应时间后结束，并释放共享资源。例如：

---

1 R 3 5
2 W 4 5
3 R 5 2
4 R 6 5
5 W 7 3

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　　测试结果：