C语言银行家算法

算法简介
银行家算法（Banker’s Algorithm）是一个避免死锁（Deadlock）的著名算法，是由艾兹格·迪杰斯特拉在1965年为T.H.E系统设计的一种避免死锁产生的算法。它以银行借贷系统的分配策略为基础，判断并保证系统的安全运行。

算法目的
为了了解系统的资源分配情况，假定系统的任何一种资源在任意时刻只能被一个进程使用，任何进程已经占用的资源只能由进程自己释放，而不能由其他进程抢占，当进程申请的资源不能满足时，必须等待。因此只要资源分配算法能保证进程的资源请求，且不出现循环等待，则系统不会出现死锁。

算法原理
在避免死锁的方法中，所施加的限制条件较弱，有可能获得令人满意的系统性能。在该方法中把系统的状态分为安全状态和不安全状态，只要能使系统始终都处于安全状态，便可以避免发生死锁。

银行家算法的基本思想是分配资源之前，判断系统是否是安全的；若是，才分配。它是最具有代表性的避免死锁的算法。

设进程cusneed提出请求REQUEST [i]，则银行家算法按如下规则进行判断。

(1)如果REQUEST [cusneed] [i]<= NEED[cusneed][i]，则转（2)；否则，出错。
(2)如果REQUEST [cusneed] [i]<= AVAILABLE[i]，则转（3)；否则，等待。
(3)系统试探分配资源，修改相关数据：
AVAILABLE[i]-=REQUEST[cusneed][i];

ALLOCATION[cusneed][i]+=REQUEST[cusneed][i];

NEED[cusneed][i]-=REQUEST[cusneed][i];

(4)系统执行安全性检查，如安全，则分配成立；否则试探险性分配作废，系统恢复原状，进程等待。
安全性检查算法

（1）设置两个工作向量Work=AVAILABLE;FINISH
（2）从进程集合中找到一个满足下述条件的进程，
FINISH==false;

NEED<=Work;

如找到，执行（3)；否则，执行（4)

(3)设进程获得资源，可顺利执行，直至完成，从而释放资源。
Work=Work+ALLOCATION;

Finish=true;

GOTO 2

原始代码：

#include
#define true 1
#define false 0
#define processNum 5
#define resourceNum 3
#define MAXINT 9999
typedef int bool;

int available[resourceNum]={3,3,2};
int maxRequest[processNum][resourceNum]={7,5,3,3,2,2,9,0,2,2,2,2,4,3,3};
int allocation[processNum][resourceNum]={0,1,0,2,0,0,3,0,2,2,1,1,0,0,2};
int need[processNum][resourceNum]={7,4,3,1,2,2,6,0,0,0,1,1,4,3,1};
bool Finish[processNum];
int safeSeries[processNum]={MAXINT, MAXINT , MAXINT , MAXINT , MAXINT};
int request[resourceNum];

void Init()
{
    int i, j;
    printf("输入进程数量、资源数量\n");
    //scanf("%d %d",&processNum,&resourceNum);
    printf("输入当前资源可用数目\n");
    for(i = 0; i < resourceNum; i++){
        scanf("%d",&available[i]);
    }
    printf("输入最大需求矩阵\n");
    for(i = 0; i < processNum; i++){
        for(j = 0; j < resourceNum; j++){
            scanf("%d",&maxRequest[i][j]);
        }
    }
    printf("输入分配矩阵\n");
    for(i = 0; i < processNum; i++){
        for(j = 0; j < resourceNum; j++){
            scanf("%d",&allocation[i][j]);
        }
    }
    printf("输入当前需求矩阵\n");
    for(i = 0; i < processNum; i++){
        for(j = 0; j < resourceNum; j++){
            scanf("%d",&need[i][j]);
        }
    }
}

void showInfo()
{
    int i,j;
    printf("当前资源剩余：");
    for(j = 0; j < resourceNum; j++){
        printf("%d ",available[j]);
    }
    printf("\n");
    printf(" PID\t Max\t\tAllocation\tNeed\n");
    for(i = 0; i < processNum; i++){
        printf(" P%d\t",i);
        for(j = 0; j < resourceNum; j++){
            printf("%d ",maxRequest[i][j]);
        }
        printf("\t\t");
        for(j = 0; j < resourceNum; j++){
            printf("%d ",allocation[i][j]);
        }
        printf("\t\t");
        for(j = 0; j < resourceNum; j++){
            printf("%d ",need[i][j]);
        }
        printf("\n");
    }
}

bool isSafe()
{
    int i,j,k;
    int trueFinished = 0;
    int work[resourceNum];
    for(i = 0; i < resourceNum; i++){
        work[i]=available[i];
    }

    for(i = 0; i < processNum; i++){
        Finish[i]=false;
    }
    i = 0;
    int temp = 0;
    while(trueFinished != processNum){
        int j =0;
        if(Finish[i]!= true){
            for(j = 0; j < resourceNum; j++){
                if(need[i][j] > work[j]){break;}
            }
        }
        if(j == resourceNum){
            Finish[i]=true;
            SafeInfo(work,i);
            for(k = 0; k < resourceNum; k++){
                work[k]+=allocation[i][k];
            }
            int k2;
            safeSeries[trueFinished++] = i;
        }
        i++;
        if(i >= processNum)
        {
            i = i % processNum;
            if(temp == trueFinished)
                break;
        }
        temp = trueFinished;
    }

    if(trueFinished == processNum){
        printf("\n系统安全！\n\n安全序列为：");
        for(i = 0; i < processNum; i++){
            printf("%d ",safeSeries[i]);
        }
        return true;
    }
    printf("******系统不安全！******\n");
    return false;
}

void SafeInfo(int *work, int i)
{
    int j;
    printf(" P%d\t",i);
    for(j = 0; j < resourceNum; j++){
        printf("%d ",work[j]);
    }
    printf("\t\t");
    for(j = 0; j < resourceNum; j++){
        printf("%d ",need[i][j]);
    }
    printf("\t ");
    for(j = 0; j < resourceNum; j++){
        printf("%d ",allocation[i][j]);
    }
    printf("\t\t");
    for(j = 0; j < resourceNum; j++){
        printf("%d ",allocation[i][j]+work[j]);
    }
    printf("\n");
}


int main()
{
    int i,j,curProcess;
    int wheInit = 0;
    printf("是否使用内置数据？0是，1否：");
    scanf("%d",&wheInit);
    if(wheInit)
        Init();  //可以不使用，选用内置的数据进行测试
    printf("---------------------------------------------------------\n");
    showInfo();
    printf("\n系统安全情况分析\n");
    printf(" PID\t Work\t\tNeed\tAllocation\tWork+Allocation\n");
    isSafe();
    while(true){
        printf("\n---------------------------------------------------------\n");
        printf("\n输入要分配的进程：");
        scanf("%d",&curProcess);
        printf("\n输入要分配给进程P%d的资源：",curProcess);
        for(j = 0; j < resourceNum; j++){
            scanf("%d", &request[j]);
        }
        for(j = 0; j < resourceNum; j++){
            if(request[j] <= need[curProcess][j])continue;
            else{printf("ERROR！\n");break;}
        }
        if(j == resourceNum){
            for(j = 0; j < resourceNum; j++){
                if(request[j] <= need[curProcess][j])continue;
                else{printf("资源不足，等待中！\n");break;}
            }
            if(j == resourceNum){
                for(j = 0; j < resourceNum; j++){
                    available[j] -= request[j];
                    allocation[curProcess][j] += request[j];
                    need[curProcess][j] -= request[j];
                }
                printf("\n系统安全情况分析\n");
                printf(" PID\t Work\t\tNeed\tAllocation\tWork+Allocation\n");
                if(isSafe()){
                    printf("分配成功！\n");
                    showInfo();
                }else{
                    for(j = 0; j < resourceNum; j++){
                        available[j] += request[j];
                        allocation[curProcess][j] -= request[j];
                        need[curProcess][j] += request[j];
                    }
                    printf("分配失败！\n");
                    showInfo();
                }
            }
        }
    }
}

修正后的代码：参考评论Sean0977

#include
#define true 1
#define false 0
#define processNum 5
#define resourceNum 3
#define MAXINT 9999
typedef int bool;

int available[resourceNum]={3,3,2};
int maxRequest[processNum][resourceNum]={7,5,3,3,2,2,9,0,2,2,2,2,4,3,3};
int allocation[processNum][resourceNum]={0,1,0,2,0,0,3,0,2,2,1,1,0,0,2};
int need[processNum][resourceNum]={7,4,3,1,2,2,6,0,0,0,1,1,4,3,1};
bool Finish[processNum];
int safeSeries[processNum]={MAXINT, MAXINT , MAXINT , MAXINT , MAXINT};
int request[resourceNum];

void Init()
{
    int i, j;
    printf("输入进程数量、资源数量\n");
    //scanf("%d %d",&processNum,&resourceNum);
    printf("输入当前资源可用数目\n");
    for(i = 0; i < resourceNum; i++){
        scanf("%d",&available[i]);
    }
    printf("输入最大需求矩阵\n");
    for(i = 0; i < processNum; i++){
        for(j = 0; j < resourceNum; j++){
            scanf("%d",&maxRequest[i][j]);
        }
    }
    printf("输入分配矩阵\n");
    for(i = 0; i < processNum; i++){
        for(j = 0; j < resourceNum; j++){
            scanf("%d",&allocation[i][j]);
        }
    }
    printf("输入当前需求矩阵\n");
    for(i = 0; i < processNum; i++){
        for(j = 0; j < resourceNum; j++){
            scanf("%d",&need[i][j]);
        }
    }
}

void showInfo()
{
    int i,j;
    printf("当前资源剩余：");
    for(j = 0; j < resourceNum; j++){
        printf("%d ",available[j]);
    }
    printf("\n");
    printf(" PID\t Max\t\tAllocation\tNeed\n");
    for(i = 0; i < processNum; i++){
        printf(" P%d\t",i);
        for(j = 0; j < resourceNum; j++){
            printf("%d ",maxRequest[i][j]);
        }
        printf("\t\t");
        for(j = 0; j < resourceNum; j++){
            printf("%d ",allocation[i][j]);
        }
        printf("\t\t");
        for(j = 0; j < resourceNum; j++){
            printf("%d ",need[i][j]);
        }
        printf("\n");
    }
}

bool isSafe()
{
    int i,j,k;
    int trueFinished = 0;
    int work[resourceNum];
    for(i = 0; i < resourceNum; i++){
        work[i]=available[i];
    }

    for(i = 0; i < processNum; i++){
        Finish[i]=false;
    }
    i = 0;
    int temp = 0;
    while(trueFinished != processNum){
        int j =0;
        if(Finish[i]!= true){
            for(j = 0; j < resourceNum; j++){
                if(need[i][j] > work[j]){break;}
            }
        }
        if(j == resourceNum){
            Finish[i]=true;
            SafeInfo(work,i);
            for(k = 0; k < resourceNum; k++){
                work[k]+=allocation[i][k];
            }
            int k2;
            safeSeries[trueFinished++] = i;
        }
        i++;
        if(i >= processNum)
        {
        	if(flag==0)
        	{
        		temp=trueFinished;
        		temp0=trueFinished;        		
			}
            i = i % processNum;         
            if(flag==1){
            temp=trueFinished;
            if(temp == temp0)
                break;
            else
            	temp0=temp;
            }        
            flag=1;
        }
        temp = trueFinished;
    }

    if(trueFinished == processNum){
        printf("\n系统安全！\n\n安全序列为：");
        for(i = 0; i < processNum; i++){
            printf("%d ",safeSeries[i]);
        }
        return true;
    }
    printf("******系统不安全！******\n");
    return false;
}

void SafeInfo(int *work, int i)
{
    int j;
    printf(" P%d\t",i);
    for(j = 0; j < resourceNum; j++){
        printf("%d ",work[j]);
    }
    printf("\t\t");
    for(j = 0; j < resourceNum; j++){
        printf("%d ",need[i][j]);
    }
    printf("\t ");
    for(j = 0; j < resourceNum; j++){
        printf("%d ",allocation[i][j]);
    }
    printf("\t\t");
    for(j = 0; j < resourceNum; j++){
        printf("%d ",allocation[i][j]+work[j]);
    }
    printf("\n");
}


int main()
{
    int i,j,curProcess;
    int wheInit = 0;
    printf("是否使用内置数据？0是，1否：");
    scanf("%d",&wheInit);
    if(wheInit)
        Init();  //可以不使用，选用内置的数据进行测试
    printf("---------------------------------------------------------\n");
    showInfo();
    printf("\n系统安全情况分析\n");
    printf(" PID\t Work\t\tNeed\tAllocation\tWork+Allocation\n");
    isSafe();
    while(true){
        printf("\n---------------------------------------------------------\n");
        printf("\n输入要分配的进程：");
        scanf("%d",&curProcess);
        printf("\n输入要分配给进程P%d的资源：",curProcess);
        for(j = 0; j < resourceNum; j++){
            scanf("%d", &request[j]);
        }
        for(j = 0; j < resourceNum; j++){
            if(request[j] <= need[curProcess][j])continue;
            else{printf("ERROR！\n");break;}
        }
        if(j == resourceNum){
            for(j = 0; j < resourceNum; j++){
                if(request[j] <= need[curProcess][j])continue;
                else{printf("资源不足，等待中！\n");break;}
            }
            if(j == resourceNum){
                for(j = 0; j < resourceNum; j++){
                    available[j] -= request[j];
                    allocation[curProcess][j] += request[j];
                    need[curProcess][j] -= request[j];
                }
                printf("\n系统安全情况分析\n");
                printf(" PID\t Work\t\tNeed\tAllocation\tWork+Allocation\n");
                if(isSafe()){
                    printf("分配成功！\n");
                    showInfo();
                }else{
                    for(j = 0; j < resourceNum; j++){
                        available[j] += request[j];
                        allocation[curProcess][j] -= request[j];
                        need[curProcess][j] += request[j];
                    }
                    printf("分配失败！\n");
                    showInfo();
                }
            }
        }
    }
}

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