银行家算法的C语言实现
银行家算法的C语言实现
近日在学习操作系统，发现国外的教材远比国内的教材更加容易理解，有时感觉操作系统是一个不折不扣的坑，书中的每一句话，其实都需要足够长的代码来描述它。
尤其是在拜读了川合秀实的三十天自制操作系统后，感觉自己对操作系统的理解不再那么抽象化了，而开始变得有血有肉起来了。
银行家算法是在系统资源有限的情况下，避免进程出现死锁的一种解决办法。
示例代码如下：
#include<stdio.h>
#include<stdlib.h>
#define TRUE 1
#define FALSE 0
int i,j,g,k;
int allocation[100][100],max[100][100],available[100];
int need[100][100];
int n_process,request[100][100],work[100],total[100];
int finish[100],temp=0;
int flag,finish_flag,safe_flag,complete_flag;
int response;
void initialize_process_resource_type();
void initialize_max();
void initialize_allocation();
void calculate_need();
void calculate_available();
void resource_request();
void safe_state_check();
void print_all();
void check_complete();
void run_time_allocation();
void release_resources();
void main()
{
initialize_process_resource_type();
initialize_max();
initialize_allocation();
calculate_need();
calculate_available();
print_all();
flag=FALSE;
while(flag==FALSE)
{
if(complete_flag==TRUE)
{
printf("\n\n All Processes has Completed");
printf(“Simulated Execution \n”);
flag=TRUE;
}
release_resources();
// system(“tput clear”);
// system(“tput clear”);
print_all();
printf("\n Enter the Run-Time Allocation…..");
run_time_allocation();
safe_state_check();
if(safe_flag==TRUE)
{
printf("\n Granting Request…..");
resource_request();
print_all();
}
else
{
printf("\n Request is not Granted !!");
printf(“This request leads to the”);
printf(“Unsafe State……..”);
}
printf("\nTry another Allocation?[y=1/n=0]:");
scanf("%d",&response);
flag=FALSE;
if(response==0) flag=TRUE;
}
printf("\n\n……Simulation of Banker’s");
printf(“Algorithm is Completed Successfully.\n”);
}
void initialize_process_resource_type()
{
printf("\nEnter the number of Processer:");
scanf("%d",&i);
printf("\nEnter the number of Types of Resources:");
scanf("%d",&j);
for(k=1;k<=j;k++)
{
printf("\nEnter the Total Resources of type %d:",k);
scanf("%d",&total[k]);
}
}
void initialize_max()
{
for(g=1;g<=i;g++)
{
for(k=1;k<=j;k++)
{
printf("\nEnter Max-Need of resource of");
printf(“type %d for Process %d:",k,g);
scanf("%d”,&max[g][k]);
}
}
}
void initialize_allocation()
{
for(g=1;g<=i;g++)
{
for(k=1;k<=j;k++)
{
printf("\nEnter Allocation of resource of");
printf(“type %d for Process %d:",k,g);
flag=FALSE;
while(flag==FALSE)
{
scanf("%d”,&allocation[g][k]);
flag=TRUE;
if(allocation[g][k]>max[g][k])
{
flag=FALSE;
printf("\nInvalid Allocation !!");
printf("\nReEnter Allocation of Resource");
printf(“of type %d for Process %d:",k,g);
}
}
}
}
}
void calculate_need()
{
for(g=1;g<=i;g++)
{
for(k=1;k<=j;k++)
{
need[g][k]=max[g][k]-allocation[g][k];
}
}
}
void calculate_available()
{
for(k=1;k<=j;k++)
{
temp=0;
for(g=1;g<=i;g++)
temp+=allocation[g][k];
available[k]=total[k]-temp;
}
}
void resource_request()
{
for(k=1;k<=j;k++)
{
if(request[n_process][k]<=need[n_process][k])
{
if(request[n_process][k]<=available[k])
{
available[k]-=request[n_process][k];
allocation[n_process][k]+=request[n_process][k];
need[n_process][k]-=request[n_process][k];
}
else
printf("\n ERROR!Availability is greater than request..”);
}
printf("\nError!! Request is greater than need…");
}
}
void safe_state_check()
{
for(k=1;k<=i;k++)
work[k]=available[k];
for(g=1;g<=i;g++)
finish[g]=FALSE;
for(g=1;g<=i;g++)
for(k=1;k<=j;k++)
{
if(finish[g]==FALSE&&need[g][k]<=work[k])
{
work[k]+=allocation[g][k];
finish[g]=TRUE;
}
}
complete_flag=TRUE;
for(g=1;g<=i;g++)
if(finish[g]==FALSE)
complete_flag=FALSE;
safe_flag=FALSE;
if(finish[n_process]==TRUE)
safe_flag=TRUE;
}
void print_all()
{
printf("\nProcess and Resource State……….");
printf("\nProcess Allocation Max Need “);
for(g=1;g<=i;g++)
{
printf("\n%d “,g);
for(k=1;k<=j;k++)
printf("%d”,allocation[g][k]);
printf(” “);
for(k=1;k<=j;k++)
printf("%d”,max[g][k]);
printf(" “);
for(k=1;k<=j;k++)
printf("%d”,need[g][k]);
}
printf("\nTotal Resources:");
for(k=1;k<=j;k++)
printf("%d",total[k]);
printf("\nAvailable:");
for(k=1;k<=j;k++)
printf("%d",available[k]);
printf("\n");
}
void check_complete()
{
complete_flag=FALSE;
}
void run_time_allocation()
{
printf("\nEnter the Process Number(1 to %d):",i);
flag=FALSE;
while(flag==FALSE)
{
flag=TRUE;
scanf("%d",&n_process);
if(n_process<1||n_process>i)
{
printf("\nReEnter the Process Number(1 to %d):",i);
flag=FALSE;
}
}
g=n_process;
for(k=1;k<=j;k++)
{
printf("\nEnter Resource of type");
printf("%d allocation for process %d:",k,g);
scanf("%d",&request[g][k]);
}
}
void release_resources()
{
for(g=1;g<=i;g++)
{
for(k=1;k<=j;k++)
{
if((allocation[g][k]==max[g][k])&&(allocation[g][k]!=0))
{
printf("\nThe Process %d is ready to deallocate",g);
printf(“Resource type %d by %dnumbers”,k,max[g][k]);
printf(“Release[y=1/n=0]:”);
scanf("%d",&response);
if(response==1)
{
available[k]+=allocation[g][k];
allocation[g][k]=0;
max[g][k]=0;
}
}
}
}
}