一名过客, 我对这个问题的理解是这样的,仅供参考,因为忙可能不会继续回复此帖,见谅-_-:
立场不同, 问题的理解也不同.
1. 超市客户的角度,我们需要描述购物过程(进门,购物,出门), 那么有多少个用户就会有多少个并发线程或进程. 也就是说每个用户就是一个独立的线程,他们之间需要用信号量进行同步.这应该适用用户作为已知条件的情况,比如已经知道张三,李四,王五等人的时候,他们就是我们描述的对象.
2. 超市运行角度, 我们同样需要描述购物过程(进门,购物,出门), 但是这时只会有两个并发线程或进程, 一个客户进门购物进程和一个客户出门进程. 超市是我们的描述目标, 超市提供了这两种服务,我们需要用信号量来同步进门和出门两种服务. 本人认为, 此题适合这种情况. 下面是我提供的这种情况的解决方案:
Semaphores:
MarketFreeSpace: 0 ~ 500, initilized to 500
CustomersInMarket: 0 ~ 500, initilized to 0
DoorsAvaiable: 0 ~ 6, intilized to 6
In:
P(MarketFreeSpace);
P(DoorsAvaiable);
Shopping();
V(CustomersInMarket);
V(DoorsAvaiable);
Out:
P(CustomersInMarket);
P(DoorsAvaiable);
Cashing();
V(MarketFreeSpace);
V(DoorsAvaiable);
附源代码:
// Semaphore.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#include "Windows.h"
HANDLE hSemSpace;
HANDLE hSemPeople;
HANDLE hSemDoors;
void InMarket(const char * threadName)
{
long lPrevCountPeople;
long lPrevCountDoors;
WaitForSingleObject(hSemSpace, INFINITE);
WaitForSingleObject(hSemDoors, INFINITE);
printf("%s: I am into market.\n", threadName);
ReleaseSemaphore(hSemPeople,1, &lPrevCountPeople);
ReleaseSemaphore(hSemDoors, 1, &lPrevCountDoors);
printf("%s: Current %d people in market.\n", threadName, lPrevCountPeople + 1);
printf("%s: Current %d doors opened.\n", threadName, lPrevCountDoors + 1);
}
void OutMarket(const char * threadName)
{
long lPrevCountSpace;
long lPrevCountDoors;
WaitForSingleObject(hSemPeople, INFINITE);
WaitForSingleObject(hSemDoors, INFINITE);
printf("%s: I am out market.\n", threadName);
ReleaseSemaphore(hSemSpace, 1, &lPrevCountSpace);
ReleaseSemaphore(hSemDoors, 1, &lPrevCountDoors);
printf("%s: Current %d doors opened.\n", threadName, lPrevCountDoors + 1);
printf("%s: Current %d free space for people in market.\n", threadName, lPrevCountSpace + 1);
}
DWORD WINAPI ThreadInMarket(LPVOID lpParameter)
{
while(TRUE)
{
InMarket("ThreadInMarket");
}
return 0;
}
DWORD WINAPI ThreadOutMarket(LPVOID lpParameter)
{
while(TRUE)
{
OutMarket("ThreadOutMarket");
}
return 0;
}
int _tmain(int argc, _TCHAR* argv[])
{
HANDLE hInMarket;
HANDLE hOutMarket;
DWORD dwWaitResult;
long lPrevCount;
setbuf(stdout, NULL);
//Open/Create semaphore
hSemSpace = CreateSemaphore(NULL, 1, 1, L"Space");
if(hSemSpace == NULL)
{
printf("CreateSemaphore \"Space\" fail, erro code:%d\n, exit", GetLastError());
return 0;
}
else
{
printf("CreateSemaphore \"Space\" succeeds.\n");
}
hSemPeople = CreateSemaphore(NULL, 0, 1, L"People");
if(hSemPeople == NULL)
{
printf("CreateSemaphore \"People\" fail, erro code:%d\n, exit", GetLastError());
return 0;
}
else
{
printf("CreateSemaphore \"People\" succeeds.\n");
}
hSemDoors = CreateSemaphore(NULL, 1, 1, L"Doors");
if(hSemDoors == NULL)
{
printf("CreateSemaphore \"Doors\" fail, erro code:%d\n, exit", GetLastError());
return 0;
}
else
{
printf("CreateSemaphore \"Doors\" succeeds.\n");
}
hInMarket = CreateThread(NULL, 0, ThreadInMarket, NULL, CREATE_SUSPENDED, NULL);
hOutMarket =CreateThread(NULL, 0, ThreadOutMarket, NULL, CREATE_SUSPENDED, NULL);
ResumeThread(hInMarket);
ResumeThread(hOutMarket);
while(TRUE)
{
Sleep(10000);
}
return 0;
}
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计算机理论与工程 → 『 计算机考研交流 』 → [求助]操作系统，PV原语的问题
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2008/1/18 11:01:00
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