操作系统实验七之有限缓冲问题

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一、实验描述

　　利用有限缓冲问题的解决思想，实现生产者消费者问题，主要利用线程同步机制完成。使用三个信号量: empty (以记录有多少空位)、full (以记录有多少满位)以及mutex (二进制信号量或互斥信号量，以保护对缓冲插入与删除的操作)。对于本项目， empty 与full 将采用标准计数信号量，而mutex 将采用二进制信号量。生产者与消费者作为独立线程，在empty、full、mutex 的同步前提下，对缓冲进行插入与删除。

二、实验测试样例

　　测试数据文件包括n行测试数据，分别描述创建的n个线程是生产者还是消费者，以及生产者或消费者存放或取产品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，P表示生产者，C表示消费者。第三字段为一个正数，表示存放或取出操作的开始时间：线程创建后，延迟相应时间(单位为秒)后发出对共享资源的使用申请。第四字段为一个正数，表示操作的持续时间。第五字段为一个正数（仅生产者有），表示生产的产品号。当线程申请成功后，开始对共享资源的操作，该操作持续相应时间后结束，并释放共享资源。例如：

1 C 3 5
2 P 4 5 1
3 C 5 2
4 C 6 5
5 P 7 3 2
6 P 8 4 3

三、知识准备

　　Linux POSIX线程互斥和同步相关知识。
　　
|：mutex初始化
线程的互斥量mutex数据类型是pthread_mutex_t。使用前要对它进行初始化，有两种方法:
(1)静态分配的互斥量的初始化：

static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER

(2)动态分配的互斥量的初始化：

首先申请内存(malloc)，再用pthread_mutex_init进行初始化。释放时，必须先调用pthread_mutex_destroy，而后再释放内存(free)。

例如：

//创建10个线程计算0～9的和。#include <stdio.h>#include <stdlib.h>#include <pthread.h>#include <errno.h>#define THREAD_NUMBER 10static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER; int sum =0;void* inc(void *arg) //线程执行的函数{   int i =(*(int *)arg);    pthread_mutex_lock(&mutex);   sum = sum +i;    pthread_mutex_unlock(&mutex);   return NULL;}int main(int argc, char *argv[]){   pthread_t pt[THREAD_NUMBER];   int i;   int arg[THREAD_NUMBER];       for(i=0; i<THREAD_NUMBER; i++) {       arg[i]=i;           if(pthread_create(&pt[i], NULL, inc, (void *)&arg[i])!=0){          printf("pthread_create error\n");          exit(1);       }          }   for(i=0; i<THREAD_NUMBER; i++)       if(pthread_join(pt[i],NULL)!=0){          printf("pthread_join error\n");          exit(1);       }   printf("sum is %d\n",sum);   pthread_mutex_destroy(&mutex);   return 0;}

|：POSIX 信号量
　　POSIX 信号量在多线程编程中可以起到同步或互斥的作用。用POSIX 信号量可以实现传统操作系统P、V操作(即对应课本的wait、signal)。
　　由于POSIX信号量不是内核负责维护，所以当进程退出后，POSIX信号量自动消亡。

#include <semaphore.h>//定义信号量sem_t  sem；//创建信号量int sem_init(sem_t *sem, int pshared, unsigned int value);//相当于wait操作，即申请资源。int sem_wait(sem_t * sem);//是函数sem_wait()的非阻塞版本。若信号量大于0，它直接将信号量sem的值减一并返回0；否则，它立即返回错误类型EAGAIN。int sem_trywait(sem_t * sem);//相当于signal操作，释放资源int sem_post(sem_t * sem);//获得信号量当前值int sem_getvalue(sem_t * sem, int * sval);//用来释放信号量int sem_destroy(sem_t * sem);

四、代码实现

buffer.h

#ifndef BUFFER_H_#define BUFFER_H_#include <iostream>#define BUFFER_SIZE 5using namespace std;typedef int buffer_item;struct Buffer{    Buffer(){        count = 0;        front = 0;        rear = 0;        for(int i = 0; i < BUFFER_SIZE; i++){            items[i] = 0;        }    }    buffer_item items[BUFFER_SIZE];    int count;    int front;    int rear;};int insert_item(buffer_item item);int remove_item();#endif

buffer.cpp

#include "buffer.h"Buffer *buffer = new Buffer();int insert_item(buffer_item item){    if(buffer->count < BUFFER_SIZE){        buffer->items[buffer->rear] = item;        cout << "Product: " << buffer->items[buffer->rear] << endl;        buffer->count++;        buffer->rear++;        if(buffer->rear % BUFFER_SIZE == 0) buffer->rear = 0;        return 0;    }    return -1;}int remove_item(){    if(buffer->count > 0){        cout<< "Consume: " << buffer->items[buffer->front] << endl;        buffer->items[buffer->front] = 0;        buffer->count--;        buffer->front++;        if(buffer->front % BUFFER_SIZE == 0) buffer->front = 0;        return 0;    }    return -1;}

deal.h

#ifndef DEAL_H_#define DEAL_H_#include <stdio.h>#include <stdlib.h>#include <string.h>#include <cstdlib>#include <iostream>using namespace std;typedef struct Data{    Data(){        serial_num = 0;        character = ' ';        start = 0;        last = 0;        product = 0;    }    int serial_num;    char character;    int start;    int last;    int product;} 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;                    case 4: ins->product = atoi(tmp.c_str());                            tmp = "";                            break;                }                j++;            }        }    }    return ins;}

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 mutex;    sem_t nempty;    sem_t nstored;};struct sto shared;void *produce(void *arg){    Instruction *ins = (Instruction*)arg;    sem_wait(&shared.nempty);    sem_wait(&shared.mutex);    sleep(ins->start);    insert_item(ins->product);    sleep(ins->last);    sem_post(&shared.mutex);    sem_post(&shared.nstored);    return(NULL);}void *consume(void *arg){    Instruction *ins = (Instruction*)arg;    sem_wait(&shared.nstored);    sem_wait(&shared.mutex);    sleep(ins->start);    remove_item();    sleep(ins->last);    sem_post(&shared.mutex);    sem_post(&shared.nempty);    return(NULL);}int main(){    FILE *fp;    char file[MAX];    int i;    pthread_t tid_produce;    pthread_t tid_consumer;    Instruction *ins = new Data();    sem_init(&shared.mutex, 0, 1);    sem_init(&shared.nempty, 0, 5);    sem_init(&shared.nstored, 0, 0);    fp = fopen("test.txt", "r");    while(fgets(file, MAX, fp)){        ins = Deal(file);        if(ins->character == 'P'){            pthread_create(&tid_produce, NULL, produce, (void*)ins);        }        else{            pthread_create(&tid_consumer, NULL, consume, (void*)ins);        }        /*cout<<ins->serial_num<<" "<<ins->character<<" ";        cout<<ins->start<<" "<<ins->last<<" ";        cout<<ins->product<<endl;*/    }    sem_destroy(&shared.mutex);    sem_destroy(&shared.nempty);    sem_destroy(&shared.nstored);    sleep(60);    return 0;}

Makefile

CC = g++objects = Main.o buffer.o deal.oMain: $(objects)    $(CC) -o Main $(objects) -pthreadMain.o: Main.cppbuffer.o: buffer.hdeal.o: deal.h.PHONY: cleanclean:    -rm Main $(objects)

五、实验结果

这里写图片描述

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