问题描述
我用内存映射文件写了一个简单的进程间通信。该代码运行得相对较好，但我将在稍后解释缓冲区的问题。这是代码（C++，Windows）：
#define UNICODE
#define _UNICODE
#include <iostream>
#include <tchar.h>
#include <Windows.h>
int wmain(int argc,wchar_t** argv)
{
if (argc != 2)
{
std::cout << "Usage: `win32mmap w` for writing,or `win32mmap r` for reading.\n";
return -1;
}
HANDLE hMapFile;
HANDLE hEvent;
HANDLE isOpened = CreateEvent(NULL,true,false,L"IsOpened"); // To check if a `win32mmap w` runs
if (wcscmp(argv[1],L"w") == 0)
{
SetEvent(isOpened);
hMapFile = CreateFileMapping(INVALID_HANDLE_VALUE,NULL,PAGE_READWRITE,1024,L"mmapFile");
if (hMapFile == NULL)
{
std::cout << "CreateFileMapping() Error: " << GetLastError() << "\n";
return GetLastError();
}
hEvent = CreateEvent(NULL,L"mmapEvent");
if (hEvent == INVALID_HANDLE_VALUE || hEvent == NULL)
{
std::cout << "CreateEvent() Error: " << GetLastError() << "\n";
return GetLastError();
}
char* buff = (char*)MapViewOfFile(hMapFile,FILE_MAP_WRITE,0);
if (!buff)
{
std::cout << "MapViewOfFile() Error: " << GetLastError() << "\n";
return GetLastError();
}
while (buff[0] != L'.')
{
std::cin >> buff;
SetEvent(hEvent);
}
UnmapViewOfFile(buff);
}
else if (wcscmp(argv[1],L"r") == 0)
{
if (WaitForSingleObject(isOpened,0) == WAIT_TIMEOUT)
{
std::cout << "Waiting for `win32mmap w`...";
WaitForSingleObject(isOpened,INFINITE);
std::cout << "\n";
}
hMapFile = OpenFileMapping(FILE_MAP_ALL_ACCESS,L"mmapFile");
if (hMapFile == NULL)
{
std::cout << "CreateFileMapping() Error: " << GetLastError() << "\n";
return GetLastError();
}
hEvent = OpenEvent(EVENT_ALL_ACCESS,L"mmapEvent");
if (hEvent == INVALID_HANDLE_VALUE || hEvent == NULL)
{
std::cout << "CreateFile() Error: " << GetLastError() << "\n";
return GetLastError();
}
char* buff = (char*)MapViewOfFile(hMapFile,FILE_MAP_READ,0);
if (!buff)
{
std::cout << "MapViewOfFile() Error: " << GetLastError() << "\n";
return GetLastError();
}
if (!buff)
{
std::cout << "MapViewOfFile() Error: " << GetLastError() << "\n";
return GetLastError();
}
while (true)
{
WaitForSingleObject(hEvent,INFINITE);
ResetEvent(hEvent);
if (buff[0] == '.')
{
break;
}
std::cout << buff << "\n";
}
UnmapViewOfFile(buff);
}
else
{
std::cout << "Usage: `win32mmap w` for writing,or `win32mmap r` for reading.\n";
return -1;
}
CloseHandle(hMapFile);
return 0;
}
该程序是一个简单的进程间通信“聊天”，它依赖于内存映射文件。要使用该程序，您需要制作该程序的两个可执行实例：win32mmap w 和win32mmap r。第一个实例用于键入在第二个实例中显示的文本。当您在第一个实例中输入 . 时，它们都会被终止。
我的问题是当我运行程序的 2 个实例时，我在第一个实例 (Hello) 中输入世界 win32mmap w，第二个实例按预期显示 Hello。但是当我在第一个实例中输入 Hello World 时，第二个实例只显示单词 World 而不是 Hello World。如何修复缓冲区将获取整个文本的代码？
解决方法
在用新数据覆盖之前，您的写入器不会等待读取器使用数据。
您需要 2 个事件 - 一个让读取器在缓冲区有数据要读取时等待发出信号，另一个让写入器在缓冲区需要数据时等待发出信号。
试试这个：
#define UNICODE
#define _UNICODE
#include <iostream>
#include <tchar.h>
#include <Windows.h>
const DWORD BufSize = 1024;
int wmain(int argc,wchar_t** argv)
{
if (argc != 2)
{
std::cout << "Usage: `win32mmap w` for writing,or `win32mmap r` for reading.\n";
return -1;
}
HANDLE hMapFile;
char* buff;
HANDLE hNeedDataEvent;
HANDLE hHasDataEvent;
DWORD dwError;
HANDLE isOpened = CreateEvent(NULL,TRUE,FALSE,L"IsOpened"); // To check if a `win32mmap w` runs
if (isOpened == NULL)
{
dwError = GetLastError();
std::cout << "CreateEvent() Error: " << dwError << "\n";
return dwError;
}
if (wcscmp(argv[1],L"w") == 0)
{
hMapFile = CreateFileMapping(INVALID_HANDLE_VALUE,NULL,PAGE_READWRITE,BufSize,L"mmapFile");
if (hMapFile == NULL)
{
dwError = GetLastError();
std::cout << "CreateFileMapping() Error: " << dwError << "\n";
SetEvent(isOpened);
return dwError;
}
buff = (char*) MapViewOfFile(hMapFile,FILE_MAP_WRITE,BufSize);
if (!buff)
{
dwError = GetLastError();
std::cout << "MapViewOfFile() Error: " << dwError << "\n";
SetEvent(isOpened);
return dwError;
}
hNeedDataEvent = CreateEvent(NULL,L"mmapNeedDataEvent");
if (hNeedDataEvent == NULL)
{
dwError = GetLastError();
std::cout << "CreateEvent() Error: " << dwError << "\n";
SetEvent(isOpened);
return dwError;
}
hHasDataEvent = CreateEvent(NULL,L"mmapHasDataEvent");
if (hHasDataEvent == NULL)
{
dwError = GetLastError();
std::cout << "CreateEvent() Error: " << dwError << "\n";
SetEvent(isOpened);
return dwError;
}
SetEvent(isOpened);
while (WaitForSingleObject(hNeedDataEvent,INFINITE) == WAIT_OBJECT_0)
{
std::cin.get(buff,BufSize);
ResetEvent(hNeedDataEvent);
SetEvent(hHasDataEvent);
if (buff[0] == L'.') break;
}
}
else if (wcscmp(argv[1],L"r") == 0)
{
if (WaitForSingleObject(isOpened,0) == WAIT_TIMEOUT)
{
std::cout << "Waiting for `win32mmap w`...";
WaitForSingleObject(isOpened,INFINITE);
std::cout << "\n";
}
hMapFile = OpenFileMapping(FILE_MAP_READ,L"mmapFile");
if (hMapFile == NULL)
{
dwError = GetLastError();
std::cout << "CreateFileMapping() Error: " << dwError << "\n";
return dwError;
}
char* buff = (char*) MapViewOfFile(hMapFile,FILE_MAP_READ,BufSize);
if (!buff)
{
dwError = GetLastError();
std::cout << "MapViewOfFile() Error: " << dwError << "\n";
return dwError;
}
hNeedDataEvent = OpenEvent(SYNCHRONIZE,L"mmapNeedDataEvent");
if (hNeedDataEvent == NULL)
{
dwError = GetLastError();
std::cout << "OpenEvent() Error: " << dwError << "\n";
return dwError;
}
hHasDataEvent = OpenEvent(SYNCHRONIZE,L"mmapHasDataEvent");
if (hHasDataEvent == NULL)
{
dwError = GetLastError();
std::cout << "OpenEvent() Error: " << dwError << "\n";
return dwError;
}
do
{
SetEvent(hNeedDataEvent);
if (WaitForSingleObject(hHasDataEvent,INFINITE) != WAIT_OBJECT_0)
break;
std::cout << buff << "\n";
ResetEvent(hHasDataEvent);
}
while (buff[0] != '.');
}
else
{
std::cout << "Usage: `win32mmap w` for writing,or `win32mmap r` for reading.\n";
return -1;
}
UnmapViewOfFile(buff);
CloseHandle(hMapFile);
CloseHandle(hNeedDataEvent);
CloseHandle(hHasDataEvent);
CloseHandle(isOpened);
return 0;
}