一、實驗描述
利用有限緩衝問題的解決思想,實現生產者消費者問題,主要利用線程同步機制完成。使用三個信號量: empty (以記錄有多少空位)、full (以記錄有多少滿位)以及mutex (二進制信號量或互斥信號量,以保護對緩衝插入與刪除的操作)。對於本項目, empty 與full 將採用標準計數信號量,而mutex 將採用二進制信號量。生產者與消費者作爲獨立線程,在empty、full、mutex 的同步前提下,對緩衝進行插入與刪除。
二、實驗測試樣例
測試數據文件包括n行測試數據,分別描述創建的n個線程是生產者還是消費者,以及生產者或消費者存放或取產品的開始時間和持續時間。每行測試數據包括四個字段,各個字段間用空格分隔。第一字段爲一個正整數,表示線程序號。第二字段表示相應線程角色,P表示生產者,C表示消費者。第三字段爲一個正數,表示存放或取出操作的開始時間:線程創建後,延遲相應時間(單位爲秒)後發出對共享資源的使用申請。第四字段爲一個正數,表示操作的持續時間。第五字段爲一個正數(僅生產者有),表示生產的產品號。當線程申請成功後,開始對共享資源的操作,該操作持續相應時間後結束,並釋放共享資源。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、知識準備
Linux POSIX線程互斥和同步相關知識。
|:mutex初始化
線程的互斥量mutex數據類型是pthread_mutex_t。 使用前要對它進行初始化,有兩種方法:
(1)靜態分配的互斥量的初始化:
static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER
(2)動態分配的互斥量的初始化:
首先申請內存(malloc),
再用pthread_mutex_init進行初始化。
釋放時,必須先調用pthread_mutex_destroy,而後再釋放內存(free)。
例如:
//創建10個線程計算0~9的和。
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <errno.h>
#define THREAD_NUMBER 10
static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
int sum =0;
void* inc(void *arg) //線程執行的函數
{
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 信號量
POSIX 信號量在多線程編程中可以起到同步或互斥的作用。用POSIX 信號量可以實現傳統操作系統P、V操作(即對應課本的wait、signal)。
由於POSIX信號量不是內核負責維護,所以當進程退出後,POSIX信號量自動消亡。
#include <semaphore.h>
//定義信號量
sem_t sem;
//創建信號量
int sem_init(sem_t *sem, int pshared, unsigned int value);
//相當於wait操作,即申請資源。
int sem_wait(sem_t * sem);
//是函數sem_wait()的非阻塞版本。若信號量大於0,它直接將信號量sem的值減一併返回0;否則,它立即返回錯誤類型EAGAIN。
int sem_trywait(sem_t * sem);
//相當於signal操作,釋放資源
int sem_post(sem_t * sem);
//獲得信號量當前值
int sem_getvalue(sem_t * sem, int * sval);
//用來釋放信號量
int sem_destroy(sem_t * sem);
四、代碼實現
buffer.h
#ifndef BUFFER_H_
#define BUFFER_H_
#include <iostream>
#define BUFFER_SIZE 5
using 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 20
struct 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.o
Main: $(objects)
$(CC) -o Main $(objects) -pthread
Main.o: Main.cpp
buffer.o: buffer.h
deal.o: deal.h
.PHONY: clean
clean:
-rm Main $(objects)