利用银行家算法避免死锁

内容导读

互联网集市收集整理的这篇技术教程文章主要介绍了利用银行家算法避免死锁，小编现在分享给大家，供广大互联网技能从业者学习和参考。文章包含5393字，纯文字阅读大概需要8分钟。

内容图文

算法思想：

代码：

#include<iostream>
#include<string>
using namespace std;
#define  numberOfProcess 5
#define  numberOfReSource 3
int *available=new int[numberOfReSource];
int *work=new int[numberOfReSource];
string *securitySequence=new string[numberOfProcess];
typedef struct pcb {
	string pName;//进程名
	string *nameOfReSource = new string[numberOfReSource];//依次存放各类资源的名称
	int *max = new int[numberOfReSource];//max[j]=K表示进程需要Rj类资源的最大数目为K
	int *allocation = new int[numberOfReSource];//allocation[j]=K表示进程已分得Rj类资源的数目为K
	int *need = new int[numberOfReSource];//need[j]=K表示进程还需要Rj类资源K个方能完成任务
	bool finish;
	struct pcb *next;//链接指针指向下一个进程
}PCB;

void printProcess(PCB* p) {//输出进程的相关信息
	PCB *q = p->next;//q指向第一个进程
	cout << endl << "所有进程的相关信息" << endl;
	cout << "         Need        Allocation    Finish" << endl;
	cout << "进程  A   B   C      A   B   C           " << endl;
	while (q) {//遍历进程
		cout << q->pName << "    ";
		cout << q->need[0] << "   " << q->need[1] << "   " << q->need[2] << "      ";
		cout << q->allocation[0] << "   " << q->allocation[1] << "   " << q->allocation[2] << "     ";
		cout << (q->finish ? "true" : "false") << endl;
		q = q->next;//q指向下一个进程
	}
	cout << endl;
}

void initProcess(PCB *p) {//初始化进程
	cout << "初始化进程" << endl;
	cout << "请依次输入资源的名称:";
	string *nameOfReSource = new string[numberOfReSource];//该变量里依次存放资源的名称
	for (int i = 0; i<numberOfReSource; i++)//依次存放各类资源的名称
		cin >> nameOfReSource[i];
	cout << "请依次输入当前可利用资源量:";
	for (int i = 0; i<numberOfReSource; i++)
		cin >> available[i];
	PCB *q = p;
	PCB *r = new PCB;//当前工作指针
	for (int i = 0; i<numberOfProcess; i++) {
		cout << "请输入进程的名字:";
		cin >> r->pName;
		cout << "请依次输入该进程的各类资源的最大需求量(例如:2 3 4 ...):";
		for (int j = 0; j<numberOfReSource; j++)
			cin >> r->max[j];
		cout << "请依次输入该进程的各类资源的已经分配量(例如:2 3 4 ...):";
		for (int j = 0; j<numberOfReSource; j++) {
			cin >> r->allocation[j];
			r->need[j] = r->max[j] - r->allocation[j];
			r->finish = false;
		}
		q->next = r;
		q = r;
		r->next = new PCB;
		r = r->next;//指针后移
	}
	r->next = NULL;
	q->next = NULL;
	q = NULL;
	delete q;//释放结点
	delete r;
	printProcess(p);//输出此时进程的相关信息
	cout << endl;
}

bool securityAlgorithm(PCB *p) {//安全性检查算法
	PCB *m = p->next;//m指向第一个结点
	PCB *s = p->next;//s指向第一个结点
	int count = 0;
	bool flag = true;
	for (int i = 0; i<numberOfReSource; i++)//初始化work变量
		work[i] = available[i];
	cout << "初始时刻work变量的值:";
	for (int j = 0; j<numberOfReSource; j++)
		cout << work[j] << " ";
	cout << endl;
	while (s) {//将所有进程的finish初始化为false
		s->finish = false;
		s = s->next;
	}
	while (true) {//安全性检测
		flag = true;
		for (int j = 0; j<numberOfReSource; j++)
			if (m->need[j]>work[j] && !m->finish) {
				flag = false;
				break;
			}
		if (flag && !m->finish) {//找到符合条件的进程
			securitySequence[count++] = m->pName;//将该进程的名称加到安全序列中
			for (int j = 0; j<numberOfReSource; j++)//修改work变量的值
				work[j] = work[j] + m->allocation[j];
			m->finish = true;//修改finish
			cout << endl << "当前选中的进程:" << m->pName << endl;
			cout << "该进程预分配后work变量的值:";//输出此刻work变量的值
			for (int j = 0; j<numberOfReSource; j++)
				cout << work[j] << " ";
			cout << endl;
		}
		m = m->next;//m指向下一个进程
		if (m == NULL)//m指向第一个进程
			m = p->next;
		s = p->next;
		flag = false;
		for (int i = 0; i<numberOfProcess; i++) {
			if (s->finish) {
				s = s->next;
				continue;
			}
			flag = true;
			for (int j = 0; j<numberOfReSource; j++)
				if (s->need[j]>work[j]) {
					flag = false;
					break;
				}
			if (flag)//当前进程符合条件
				break;
			s = s->next;
		}
		if (!flag)//退出整个循环
			break;
	}
	flag = true;
	s = p->next;
	for (int i = 0; i<numberOfProcess; i++) {
		if (!s->finish) {
			flag = false;
			break;
		}
		s = s->next;
	}
	if (flag) {//全为true
		cout << endl << "当前系统是安全的" << endl;
		cout << "安全序列:";
		for (int i = 0; i<numberOfProcess; i++)
			cout << securitySequence[i] << " ";
		cout << endl;
		printProcess(p);
		return true;
	}
	else {//不全为false
		cout << "当前系统是不安全的" << endl;
		printProcess(p);
		return false;
	}
}

int main() {
	PCB *p = new PCB;
	PCB *q;
	initProcess(p);//初始化操作
	securityAlgorithm(p);//安全性检测
	string nameOfRequestResource;//请求资源的进程名
	int *requestResource = new int[numberOfReSource];
	bool flag = true;
	while (true) {
		cout << endl << "请输入发出请求资源的进程的名字:";
		cin >> nameOfRequestResource;
		cout << "请依次输入请求向量:";
		for (int i = 0; i<numberOfReSource; i++) {
			cin >> requestResource[i];
		}
		q = p->next;
		while (q) {//找到当前进程
			if (q->pName == nameOfRequestResource)
				break;
			q = q->next;
		}
		cout << endl << "银行家算法开始进行检查" << endl << endl;
		flag = true;
		for (int i = 0; i<numberOfReSource; i++) {
			if (requestResource[i]>q->need[i] || requestResource[i]>available[i]) {
				flag = false;
				break;
			}
		}
		if (flag) {//符合条件
			cout << "银行家算法检查过后发现符合要求" << endl << endl;
			for (int i = 0; i<numberOfReSource; i++) {
				available[i] -= requestResource[i];
				q->allocation[i] += requestResource[i];
				q->need[i] -= requestResource[i];
			}
			cout << "下面进行安全性算法检查" << endl << endl;
			if (!securityAlgorithm(p))//当前系统处于不安全状态
				for (int i = 0; i<numberOfReSource; i++) {
					available[i] += requestResource[i];
					q->allocation[i] -= requestResource[i];
					q->need[i] += requestResource[i];
				}
		}
		else//不符合条件
			cout << "银行家算法检查之后发现不符合要求" << endl << endl;
		cout << endl;
		string choose;
		cout << endl << "是否还有进程要申请资源,若是则输入YES，否则输入NO:";
		cin >> choose;
		if (choose == "NO")
			break;
	}
	q = NULL;
	delete q;
	return 0;
}

结果：

内容总结

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