Archive for 4 月, 2005
与老师探讨问题
彭老师：
又来麻烦您了，上次您给我说了关于“约瑟夫问题”的程序以后，我开始注意自己的程序结构的合理性安排。两次上机作业“多项式操作”和“表达式计算”都做好了，这些天终于把“银行的模拟”做好了，请老师看看。我下面大体说一下程序的思路。
首先，我当然用到了“队列”，因为这个程序是“队列”的应用嘛。我使用了2种队列，分别装“刚进入银行的人”和“在某个队上排队的人”，在程序里面是BankIndoor和BankQueue。关于事件的驱动，我思考了很久，最终我采用了一个存放“函数指针”的链表：
1 2 3 4 5 6 | typedef struct MethodStruct { METHODCALLBACK (*todo)(); METHODSTATE state; MethodStruct *next; }MethodNode; |
把 每一次要触发的事件都存在这个链表里面，而每一个基本时间段里，都由EnumerateAllMethod()这个函数通过遍历链表来达到出发所有事件的 作用。EnumerateAllMethod通过这个链表每一个节点的state值来判断当前是否激发这个事件。通过这个方法就很容易随机地产生顾客。比 如CustomerArrival()这个函数，每次都产生一个随机数，用于EnumerateAllMethod()判断下一次调用它的时间。关于这种 思路，其实我是参考了Windows的消息触发机制。
在这个事件的链表里面，有三个很重要的事件是CustomerArrival()、 CustomerQueue()、CustomerTODO()。分别处理顾客到来，顾客分队，顾客办理事务这三个事件。这三个函数互相不影响。都由 EnumerateAllMethod统一调用，并且各自监视各自的队列。
最后要说的是关于银行关门的处理，银行到达运营时间的时候产生 READYFORCLOSED的标识，这个时候CustomerArrival()就不触发了，而只触发CustomerQueue()、 CustomerTODO()。当CustomerTODO()检查到所有队列都没有顾客了的时候，就把银行标识改为CLOSED，这样就解决了这个问 题。
通过这次练习，我学到了很多东西，不过也萌发了用C语言来实现事件机制的想法，呵呵，但是我还是觉得有一些难。
程序在Visual C++.NET 2003和Dev-C++下均调试通过。程序运行时间为30秒（可以通过修改#define CLOSETIME 30来进行更改）。
源代码：
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 | #include <stdio.h> #include <time.h> #include <stdlib.h> //**************************************** #define WAIT_INDOOR 1 #define WAIT_QUEUE 2 #define QUEUES 5 #define FAILED 0 #define SUCCEEDED 1 #define OPEN 1 #define CLOSED 0 #define READYFORCLOSED 2 #define OVERFLOW 2 #define CLOSETIME 30 #define MINTIMEARRIVAL 2 #define MINTIMETODO 10 typedef int EVENTTYPE; typedef int METHODSTATE; typedef int METHODCALLBACK; typedef long SYSTEMTIME; typedef int STATUS; typedef int BANKSTATE; typedef int CustomerID; //**************************************** typedef struct EventStruct { EVENTTYPE detail; SYSTEMTIME occurtime; CustomerID ID; }EventNode; typedef EventNode *Event; typedef struct QueueStruct { EventNode item; QueueStruct *next; }QueueNode; typedef QueueNode *QueuePtr; typedef struct{ QueuePtr front; QueuePtr rear; }LinkQueue; typedef struct CustomerStruct { SYSTEMTIME arrivaltime; SYSTEMTIME duration; }CustomerNode; typedef struct MethodStruct { METHODCALLBACK (*todo)(); METHODSTATE state; MethodStruct *next; }MethodNode; typedef MethodNode *MethodLink; //***************************************** LinkQueue BankIndoor; LinkQueue BankQueue[QUEUES]; MethodLink Methods; SYSTEMTIME BankClock; BANKSTATE BankState; time_t StartTime,EndTime; CustomerID IDSeed; //***************************************** STATUS InitQueue(LinkQueue &Q) { Q.front=Q.rear=new QueueNode; if (!Q.front) exit(OVERFLOW); Q.front->next=NULL; return SUCCEEDED; } STATUS DestroyQueue(LinkQueue &Q) { while(Q.front) { Q.rear=Q.front->next; delete Q.front; Q.front=Q.rear; } return SUCCEEDED; } STATUS EnQueue(LinkQueue &Q,Event e) { QueuePtr p; p=new QueueNode; if (!p) exit(OVERFLOW); p->item=*e;p->next=NULL; Q.rear->next=p; Q.rear=p; return SUCCEEDED; } STATUS DeQueue(LinkQueue &Q,Event &e) { QueuePtr p; if(Q.front==Q.rear) return FAILED; p=Q.front->next; *e=p->item; Q.front->next=p->next; if (Q.rear==p) Q.rear=Q.front; delete p; return SUCCEEDED; } int QueueLength(LinkQueue Q) { int numbers=0; while(Q.front!=Q.rear) { Q.front=Q.front->next; numbers++; } return numbers; } int PlaceCustomer() { int min=0; for (int i=0;i<QUEUES;i++) { if(QueueLength(BankQueue[i])<=QueueLength(BankQueue[min])) min=i; } return min; } //***************************************** METHODCALLBACK CustomerArrival() { SYSTEMTIME nexttime; Event node; if (BankState==READYFORCLOSED) return 32767; node=new EventNode; node->detail=WAIT_INDOOR; node->occurtime=BankClock; node->ID=IDSeed++; srand((unsigned)time(0)); nexttime=rand()%MINTIMEARRIVAL; EnQueue(BankIndoor,node); printf("Customer %d arrived in %d\n",node->ID,BankClock); delete node; return nexttime; } METHODCALLBACK CustomerQueue() { Event node; int nexttime; node=new EventNode; if (DeQueue(BankIndoor,node)!=FAILED) { node->detail=WAIT_QUEUE; srand((unsigned)time(0)); nexttime=rand()%MINTIMETODO+1; node->occurtime=nexttime; printf("Customer %d placed in queue %d(%d)\n",node->ID,PlaceCustomer(),nexttime); EnQueue(BankQueue[PlaceCustomer()],node); } delete node; return 0; } METHODCALLBACK CustomerTODO() { Event node; int counter=0; node=new EventNode; for (int i=0;i<QUEUES;i++) { if (DeQueue(BankQueue[i],node)!=FAILED) { //printf("%d\n",node->occurtime); if (node->occurtime<=0) { printf("Customer %d has left from queue %d\n",node->ID,i); } else { node->occurtime--; EnQueue(BankQueue[i],node); } counter++; } } delete node; if (counter==0&&BankState==READYFORCLOSED) BankState=CLOSED; return 0; } //判断是否到了停止营业的时间 METHODCALLBACK CheckForClose() { if(BankClock==CLOSETIME) { BankState=READYFORCLOSED; printf("The bank is ready for close.\n"); } return 0; } //时钟 METHODCALLBACK Clock() { BankClock++; return 0; } //**************************************** STATUS InitMethods() { if (Methods==NULL) { Methods=new MethodNode; Methods->state=0; Methods->next=NULL; Methods->todo=Clock; return SUCCEEDED; } else return FAILED; } STATUS RegisterMethod(METHODCALLBACK (*m)()) { MethodLink pointer; MethodLink node; pointer=Methods; while(pointer->next!=NULL) pointer=pointer->next; node=new MethodNode; if (node==NULL) return FAILED; node->state=0; node->next=NULL; node->todo=m; pointer->next=node; return SUCCEEDED; } STATUS RegisterAllMethod() { RegisterMethod(CheckForClose); RegisterMethod(CustomerArrival); RegisterMethod(CustomerQueue); RegisterMethod(CustomerTODO); return SUCCEEDED; } STATUS DeleteAllMethod() { MethodLink pointer; MethodLink node; pointer=Methods; while(pointer->next!=NULL) { node=pointer; pointer=pointer->next; delete node; } return SUCCEEDED; } STATUS EnumerateAllMethod() { MethodLink pointer; pointer=Methods; time(&EndTime); if (difftime(EndTime,StartTime)>=1.0) { time(&StartTime); while(pointer!=NULL) { if(pointer->state==0) pointer->state=pointer->todo(); else pointer->state--; pointer=pointer->next; } } return SUCCEEDED; } STATUS OpenForTheDay() { BankClock=0; BankState=OPEN; IDSeed=0; //********************** InitMethods(); RegisterAllMethod(); InitQueue(BankIndoor); for (int i=0;i<QUEUES;i++) InitQueue(BankQueue[i]); time(&StartTime); printf("The bank is open.\n"); return SUCCEEDED; } STATUS CloseForTheDay() { DestroyQueue(BankIndoor); for(int i=0;i<QUEUES;i++) DestroyQueue(BankQueue[i]); DeleteAllMethod(); printf("The bank is closed.\n"); return SUCCEEDED; } //***************************************** int main() { OpenForTheDay(); while(BankState!=CLOSED) { EnumerateAllMethod(); } CloseForTheDay(); system("PAUSE"); return 0; } |
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