c.cpp

本程序可以用于实现操作系统中有关pv操作的演示的.

#include <stdio.h>
#include <Windows.h>
//缓冲区和信号量
HANDLE g_hBuffer = NULL;
HANDLE g_hSemSynR = NULL, g_hSemSynM = NULL, g_hSemSynP = NULL,g_hSemMutex = NULL;
char* g_pszBuffer = NULL;
//在缓冲区中的位置指针
unsigned char g_nR = 0, g_nM = 0, g_nP = 0;
//P,V操作
void P(HANDLE hSem)
{  
	WaitForSingleObject(hSem, INFINITE);
}
void V(HANDLE hSem)
{  
	ReleaseSemaphore(hSem, 1, NULL);
}
void main()
{//创建共享内存,大小为320 + 3B=10条记录 + 3个指针
	g_hBuffer= CreateFileMapping((HANDLE)0xFFFFFFFF, NULL,PAGE_READWRITE, 0, 323, "my_buffer");
	if(g_hBuffer == NULL)// 如果创建失败
	{  
		printf("创建或连接共享内存失败!\n");
		return;  
	}
	else if(GetLastError()==ERROR_ALREADY_EXISTS)
	{//如果已经存在这个同名对象, 说明共享内存已经创建
		g_pszBuffer=(char*)MapViewOfFile(g_hBuffer,FILE_MAP_WRITE | FILE_MAP_READ, 0,0,0);
		unsigned char *pnPoint = (unsigned char*)g_pszBuffer;
		g_nR = pnPoint[0];
		g_nM = pnPoint[1];
		g_nP = pnPoint[2];
	}
	else 
	{// 经过上面的检查, 说明这是第一次创建共享内存
		g_pszBuffer=(char*)MapViewOfFile(g_hBuffer, FILE_MAP_WRITE | FILE_MAP_READ, 0,0,0);
		// 初始化内存
		memset(g_pszBuffer, 0, 323);
		g_nR = g_nM = g_nP = 0;
	}
//创建信号量
	g_hSemSynR=CreateSemaphore(NULL, 10, 10, "my_sem_R");
	g_hSemSynM=CreateSemaphore(NULL, 0, 10, "my_sem_M");
	g_hSemSynP=CreateSemaphore(NULL, 0, 10, "my_sem_P");
	g_hSemMutex=CreateSemaphore(NULL, 0, 1, "my_sem_C");
	if(g_hSemSynR == NULL || g_hSemSynM == NULL || g_hSemSynP == NULL)	
	{// 如果创建失败 
		printf("创建或连接信号量失败!\n");
		return;  
	}//以上的代码对所有的程序都是一样的
	UnmapViewOfFile(g_pszBuffer);//断开和共享内存的连接
	CloseHandle(g_hBuffer);//关闭这个句柄
	return;
}