银行家算法1.docx
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银行家算法1.docx
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银行家算法1
一个进程序列{P1,…,Pn}是安全的,如果对于每一个进程Pi(1≤i≤n),它以后尚需要的资源量不超过系统当前剩余资源量与所有进程Pj(j
银行家算法:
我们可以把操作系统看作是银行家,操作系统管理的资源相当于银行家管理的资金,进程向操作系统请求分配资源相当于用户向银行家贷款。
操作系统按照银行家制定的规则为进程分配资源,当进程首次申请资源时,要测试该进程对资源的最大需求量,如果系统现存的资源可以满足它的最大需求量则按当前的申请量分配资源,否则就推迟分配。
当进程在执行中继续申请资源时,先测试该进程已占用的资源数与本次申请的资源数之和是否超过了该进程对资源的最大需求量。
若超过则拒绝分配资源,若没有超过则再测试系统现存的资源能否满足该进程尚需的最大资源量,若能满足则按当前的申请量分配资源,否则也要推迟分配。
算法:
n:
系统中进程的总数
m:
资源类总数
Available:
ARRAY【1..m】ofinteger;
Max:
ARRAY【1..n,1..m】ofinteger;
Allocation:
ARRAY【1..n,1..m】ofinteger;
Need:
ARRAY【1..n,1..m】ofinteger;
Request:
ARRAY【1..n,1..m】ofinteger;
简记符号:
Available
Max
Allocation
Need
Request
当进程pi提出资源申请时,系统执行下列
步骤:
(1)若Request≤Need,转
(2);
否则错误返回
(2)若Request≤Available,
转(3);否则进程等待
(3)假设系统分配了资源,则有:
Available:
=Available-Request;
Allocation:
=
Allocation+Request;
Need:
=Need-Request
若系统新状态是安全的,则分配完成
若系统新状态是不安全的,则恢复原状
态,进程等待
为进行安全性检查,定义数据结构:
Work:
ARRAY【1..m】ofinteger;
Finish:
ARRAY【1..n】ofBoolean;
安全性检查的步骤:
(1)Work:
=Available;
Finish:
=false;
(2)寻找满足条件的i:
a.Finish=false;
b.Need≤Work;
如果不存在,则转(4)
(3)Work:
=Work+Allocation;
Finish:
=true;
转
(2)
(4)若对所有i,Finish=true,则系
统处于安全状态,否则处于不安全
状态
/*银行家算法,操作系统概念(OSconceptsSixEdition)
作者:
ctu_85
*/
#include"malloc.h"
#include"stdio.h"
#definealloclensizeof(structallocation)
#definemaxlensizeof(structmax)
#defineavalensizeof(structavailable)
#defineneedlensizeof(structneed)
#definefinilensizeof(structfinish)
#definepathlensizeof(structpath)
structallocation
{
intvalue;
structallocation*next;
};
structmax
{
intvalue;
structmax*next;
};
structavailable
{
intvalue;
structavailable*next;
};
structneed
{
intvalue;
structneed*next;
};
structpath
{
intvalue;
structpath*next;
};
structfinish
{
intstat;
structfinish*next;
};
intmain()
{
introw,colum,status=0,i,j,t,temp,processtest;
structallocation*allochead,*alloc1,*alloc2,*alloctemp;
structmax*maxhead,*maxium1,*maxium2,*maxtemp;
structavailable*avahead,*available1,*available2,*availabletemp,*workhead,*work1,*work2,*worktemp,*worktemp1;
structneed*needhead,*need1,*need2,*needtemp;
structfinish*finihead,*finish1,*finish2,*finishtemp;
structpath*pathhead,*path1,*path2,*pathtemp;
charc;
printf("\nPleaseenterthetypeofsourcesthesystemhas:
\n");
scanf("%d",&colum);
printf("Pleaseenterthenumberofprocessesnowinthememory:
\n");
scanf("%d",&row);
printf("Pleaseentertheallocationarray:
\n");
for(i=0;i { printf("Theallocationforprocessp%d: \n",i); for(j=0;j { printf("Thetype%csystemresourceallocated: \n",'A'+j); if(status==0) { allochead=alloc1=alloc2=(structallocation*)malloc(alloclen); alloc1->next=alloc2->next=NULL; scanf("%d",&allochead->value); status++; } else { alloc2=(structallocation*)malloc(alloclen); scanf("%d,%d",&alloc2->value); if(status==1) { allochead->next=alloc2; status++; } alloc1->next=alloc2; alloc1=alloc2; } } } alloc2->next=NULL; status=0; printf("Pleaseenterthemaxarray: \n"); for(i=0;i { printf("Themaxneededfromprocessp%d: \n",i); for(j=0;j { printf("Thetype%cmaxiumsystemresourcemayneeded: \n",'A'+j); if(status==0) { maxhead=maxium1=maxium2=(structmax*)malloc(maxlen); maxium1->next=maxium2->next=NULL; scanf("%d",&maxium1->value); status++; } else { maxium2=(structmax*)malloc(maxlen); scanf("%d,%d",&maxium2->value); if(status==1) { maxhead->next=maxium2; status++; } maxium1->next=maxium2; maxium1=maxium2; } } } maxium2->next=NULL; status=0; printf("Pleaseentertheavailablearraynowexistsinthesystem: \n"); for(j=0;j { printf("Thetype%cavailablesystemresourcenumber: \n",'A'+j); if(status==0) { avahead=available1=available2=(structavailable*)malloc(avalen); workhead=work1=work2=(structavailable*)malloc(avalen); available1->next=available2->next=NULL; work1->next=work2->next=NULL; scanf("%d",&available1->value); work1->value=available1->value; status++; } else { available2=(structavailable*)malloc(avalen); work2=(structavailable*)malloc(avalen); scanf("%d,%d",&available2->value); work2->value=available2->value; if(status==1) { avahead->next=available2; workhead->next=work2; status++; } available1->next=available2; available1=available2; work1->next=work2; work1=work2; } } available2->next=NULL; work2->next=NULL; status=0; alloctemp=allochead; maxtemp=maxhead; for(i=0;i for(j=0;j { if(status==0) { needhead=need1=need2=(structneed*)malloc(needlen); need1->next=need2->next=NULL; need1->value=maxtemp->value-alloctemp->value; status++; } else { need2=(structneed*)malloc(needlen); need2->value=(maxtemp->value)-(alloctemp->value); if(status==1) { needhead->next=need2; status++; } need1->next=need2; need1=need2; } maxtemp=maxtemp->next; alloctemp=alloctemp->next; } need2->next=NULL; status=0; for(i=0;i { if(status==0) { finihead=finish1=finish2=(structfinish*)malloc(finilen); finish1->next=finish2->next=NULL; finish1->stat=0; status++; } else { finish2=(structfinish*)malloc(finilen); finish2->stat=0; if(status==1) { finihead->next=finish2; status++; } finish1->next=finish2; finish1=finish2; } } finish2->next=NULL;/*Initializationcompleated*/ status=0; processtest=0; for(temp=0;temp { alloctemp=allochead; needtemp=needhead; finishtemp=finihead; worktemp=workhead; for(i=0;i { worktemp1=worktemp; if(finishtemp->stat==0) { for(j=0;j if(needtemp->value<=worktemp->value) processtest++; if(processtest==colum) { for(j=0;j { worktemp1->value+=alloctemp->value; worktemp1=worktemp1->next; alloctemp=alloctemp->next; } if(status==0) { pathhead=path1=path2=(structpath*)malloc(pathlen); path1->next=path2->next=NULL; path1->value=i; status++; } else { path2=(structpath*)malloc(pathlen); path2->value=i; if(status==1) { pathhead->next=path2; status++; } path1->next=path2; path1=path2; } finishtemp->stat=1; } else { for(t=0;t alloctemp=alloctemp->next; finishtemp->stat=0; } } else for(t=0;t { needtemp=needtemp->next; alloctemp=alloctemp->next; } processtest=0; worktemp=workhead; finishtemp=finishtemp->next; } } path2->next=NULL; finishtemp=finihead; for(temp=0;temp { if(finishtemp->value==0) { printf("\nWARNING,thesystemisinnonsafestatus! \n"); exit(0); } finishtemp=finishtemp->next; } printf("\nThesystemisinsafestatus! \n"); printf("\nThesafesequenceis: \n"); do { printf("p%d",pathhead->value); } while(pathhead=pathhead->next); }
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