操作系统实验九之写者优先问题

一、代码实现

读者进程和写者进程如下：
Main.cpp

#include <pthread.h>#include <sys/types.h>#include <semaphore.h>#include <unistd.h>#include "buffer.h"#include "deal.h"#define MAX 20struct sto{    sem_t mutex1;//保证read操作原子性    sem_t mutex2;//保证write操作原子性    sem_t single;//保证每次只有一个读者进入临界区。这样，写者即到即写(只用等一个人)。    sem_t r;//读者是否可以读；可以读时r>0.    sem_t wrt;//写者是否可以读取共享数据段};struct sto shared;int readcount;int writecount;void *Read(void *arg){    Instruction *ins = (Instruction*)arg;    sleep(ins->start);//等待一段时间，开始申请资源    sem_wait(&shared.single);//只有一个读者准备进入临界区，其他被阻塞    sem_wait(&shared.r); //最后一个写者完成操作，则把权利交还给读者    sem_wait(&shared.mutex1);//保证操作原子性    readcount++;    if(readcount == 1) sem_wait(&shared.wrt);//为了保证在读取期间，没有写者操作数据;互斥    sem_post(&shared.mutex1);    sem_post(&shared.r);//给写者创造占领先机的机会    sem_post(&shared.single);    //开始读取共享数据段    cout<<"Reader "<<ins->serial_num<<" is reading."<<endl;    sleep(ins->last);    cout<<"Reader "<<ins->serial_num<<" end reading."<<endl;    //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.mutex1);    readcount--;    if(readcount == 0) sem_post(&shared.wrt);    sem_post(&shared.mutex1);    return(NULL);}void *Write(void *arg){    Instruction *ins = (Instruction*)arg;    sleep(ins->start);    //来一个写者，写者数量即加1    sem_wait(&shared.mutex2);    writecount++;    if(writecount == 1) sem_wait(&shared.r);    sem_post(&shared.mutex2);    //写者读取共享数据段    sem_wait(&shared.wrt);    cout<<"Writer "<<ins->serial_num<<" is writing."<<endl;    sleep(ins->last);    cout<<"Writer "<<ins->serial_num<<" end writing."<<endl;    sem_post(&shared.wrt);    //如果所有写者写完，把权利交还读者    sem_wait(&shared.mutex2);    writecount--;    if(writecount == 0) sem_post(&shared.r);    sem_post(&shared.mutex2);    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.mutex1, 0, 1);    sem_init(&shared.mutex2, 0, 1);    sem_init(&shared.single, 0, 1);    sem_init(&shared.wrt, 0, 1);    sem_init(&shared.r, 0, 1);    readcount = 0;    writecount = 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<<ins->serial_num<<" "<<ins->character<<" ";        cout<<ins->start<<" "<<ins->last<<" ";        cout<<endl;*/    }    sem_destroy(&shared.mutex1);    sem_destroy(&shared.mutex2);    sem_destroy(&shared.wrt);    sem_destroy(&shared.r);    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 <stdio.h>#insem_destroy(&shared.mutex2);    sem_destroy(&shared.wrt);    sem_destroy(&shared.r);    sleep(50);    return 0;}clude <stdlib.h>#include <string.h>#include <cstdlib>#include <iostream>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：

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

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　　实验结果如图：