【计算机专业】操作系统 银行家算法详解.doc

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1、银行家算法 开放分类： 算法 银行家算法是一种最有代表性的避免死锁的算法。要解释银行家算法，必须先解释操作系统安全状态和不安全状态。安全状态：如果存在一个由系统中所有进程构成的安全序列P1，Pn，则系统处于安全状态。安全状态一定是没有死锁发生。不安全状态:不存在一个安全序列。不安全状态一定导致死锁。那么什么是安全序列呢？安全序列：一个进程序列P1，Pn是安全的，如果对于每一个进程Pi(1in），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 i )当前占有资源量之和。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

2、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:ARRAY1.m of integer;Max:ARRAY1.n,1.m of i

3、nteger;Allocation:ARRAY1.n,1.m of integer;Need:ARRAY1.n,1.m of integer;Request:ARRAY1.n,1.m of integer;简记符号：AvailableMaxAllocationNeedRequest当进程pi提出资源申请时，系统执行下列步骤：（1）若RequestNeed,转（2）；否则错误返回（2）若RequestAvailable,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;Ne

4、ed:=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:ARRAY1.m of integer;Finish:ARRAY1.n of Boolean;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.NeedWork;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

5、/* 银行家算法，操作系统概念(OS concepts Six Edition)作者：ctu_85*/#include malloc.h#include stdio.h#define alloclen sizeof(struct allocation)#define maxlen sizeof(struct max)#define avalen sizeof(struct available)#define needlen sizeof(struct need)#define finilen sizeof(struct finish)#define pathlen sizeof(struct

6、path)struct allocationint value;struct allocation *next;struct maxint value;struct max *next;struct availableint value;struct available *next;struct needint value;struct need *next;struct pathint value;struct path *next;struct finishint stat;struct finish *next;int main()int row,colum,status=0,i,j,t

7、,temp,processtest;struct allocation *allochead,*alloc1,*alloc2,*alloctemp;struct max *maxhead,*maxium1,*maxium2,*maxtemp;struct available *avahead,*available1,*available2,*availabletemp,*workhead,*work1,*work2,*worktemp,*worktemp1;struct need *needhead,*need1,*need2,*needtemp;struct finish *finihead

8、,*finish1,*finish2,*finishtemp;struct path *pathhead,*path1,*path2,*pathtemp;char c;printf(nPlease enter the type of sources the system has:n);scanf(%d,&colum);printf(Please enter the number of processes now in the memory:n);scanf(%d,&row);printf(Please enter the allocation array:n);for(i=0;irow;i+)

9、printf(The allocation for process p%d:n,i);for (j=0;jnext=alloc2-next=NULL;scanf(%d,&allochead-value);status+;elsealloc2=(struct allocation *)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(Please

10、 enter the max array:n);for(i=0;irow;i+)printf(The max needed from process p%d:n,i);for (j=0;jnext=maxium2-next=NULL;scanf(%d,&maxium1-value);status+;elsemaxium2=(struct max *)malloc(maxlen);scanf(%d,%d,&maxium2-value);if(status=1)maxhead-next=maxium2;status+;maxium1-next=maxium2;maxium1=maxium2;max

11、ium2-next=NULL;status=0;printf(Please enter the available array now exists in the system:n);for (j=0;jnext=available2-next=NULL;work1-next=work2-next=NULL;scanf(%d,&available1-value);work1-value=available1-value;status+;elseavailable2=(struct available*)malloc(avalen);work2=(struct available*)malloc

12、(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

13、;irow;i+)for (j=0;jnext=need2-next=NULL;need1-value=maxtemp-value-alloctemp-value;status+;elseneed2=(struct need *)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-ne

14、xt=NULL;status=0;for(i=0;inext=finish2-next=NULL;finish1-stat=0;status+;elsefinish2=(struct finish*)malloc(finilen);finish2-stat=0;if(status=1)finihead-next=finish2;status+;finish1-next=finish2;finish1=finish2;finish2-next=NULL; /*Initialization compleated*/status=0;processtest=0;for(temp=0;temprow;

15、temp+)alloctemp=allochead;needtemp=needhead;finishtemp=finihead;worktemp=workhead;for(i=0;istat=0)for(j=0;jnext,worktemp=worktemp-next)if(needtemp-valuevalue)processtest+;if(processtest=colum)for(j=0;jvalue+=alloctemp-value;worktemp1=worktemp1-next;alloctemp=alloctemp-next;if(status=0)pathhead=path1

16、=path2=(struct path*)malloc(pathlen);path1-next=path2-next=NULL;path1-value=i;status+;elsepath2=(struct path*)malloc(pathlen);path2-value=i;if(status=1)pathhead-next=path2;status+;path1-next=path2;path1=path2;finishtemp-stat=1;elsefor(t=0;tnext;finishtemp-stat=0;elsefor(t=0;tnext;alloctemp=alloctemp

17、-next;processtest=0;worktemp=workhead;finishtemp=finishtemp-next;path2-next=NULL;finishtemp=finihead;for(temp=0;tempvalue=0)printf(nWARNING,the system is in nonsafe status!n);exit(0);finishtemp=finishtemp-next;printf(nThe system is in safe status!n);printf(nThe safe sequence is: n);doprintf(p%d ,pathhead-value);while(pathhead=pathhead-next);