异步IO操作与同步操作区别：

1. 在CreateFile里的FILE_FLAG_OVERLAPPED标志
2. 异步操作函数LPOVERLAPPED参数

接收IO请求完成通知

1. 触发设备内核对象
   缺点：同一个设备内核对象有可能进行多次读写操作，这样第一个完成这个设备内核对象就会被触发，所以这种方式不可以使用于这种情形
   

   void Test1()
   {
       HANDLE hFile = ::CreateFile(_T("aaa.txt"),
           GENERIC_READ,
           FILE_SHARE_READ,
           NULL,
           OPEN_EXISTING,
           FILE_FLAG_OVERLAPPED,
           NULL);
       if(!hFile)
       {
           wcout<<L"CreateFile Failed ErroCode:"<<::GetLastError()<<endl;
           return ;
       }
       DWORD dwFileSize = ::GetFileSize(hFile,0);
       wcout<<L"FileSize:"<<dwFileSize<<endl;
       char * pFileContent = new char[10000000];
       DWORD dwReaded = 0;
       OVERLAPPED o_Read = {0};
       DWORD bReadDone = ::ReadFile(hFile,
           pFileContent,
           10000000,
           &dwReaded,
           &o_Read);
       DWORD dwError = ::GetLastError();
       if(!bReadDone && (dwError == ERROR_IO_PENDING))
       {
           WaitForSingleObject(hFile,INFINITE);
           bReadDone = TRUE;
       }
   
       if(bReadDone)
           wcout<<L"I/O Code:"<<o_Read.Internal<<" TransedBytes:"<<o_Read.InternalHigh<<endl;
       else
           wcout<<"Error:"<<::GetLastError()<<endl;
       ::CloseHandle(hFile);
       delete [] pFileContent;
   }

2. 触发事件内核对象
   

   void Test2()
   {
       HANDLE hFile = ::CreateFile(_T("aaa.txt"),
           GENERIC_WRITE,
           FILE_SHARE_READ,
           NULL,
           OPEN_EXISTING,
           FILE_FLAG_OVERLAPPED,
           NULL);
       if(!hFile)
       {
           wcout<<L"CreateFile Failed ErroCode:"<<::GetLastError()<<endl;
           return ;
       }
       DWORD dwFileSize = ::GetFileSize(hFile,0);
       wcout<<L"FileSize:"<<dwFileSize<<endl;
       LARGE_INTEGER liDis = {0};
       LARGE_INTEGER liRet = {0};
       ::SetFilePointerEx(hFile,liDis,&liRet,FILE_END);
       wcout<<L"PreWrite File Pos:"<<liRet.LowPart<<endl;
       char * pFileContent = new char[10000000];
       memset(pFileContent,‘z‘,10000000);
       DWORD dwReaded = 0;
       OVERLAPPED o_Write = {0};
       o_Write.Offset = liRet.LowPart;
       o_Write.hEvent = ::CreateEvent(NULL,FALSE,FALSE,NULL);
       DWORD bReadDone = ::WriteFile(hFile,
           pFileContent,
           10000000,
           &dwReaded,
           &o_Write);
       DWORD dwError = ::GetLastError();
       if(!bReadDone && (dwError == ERROR_IO_PENDING))
       {
           WaitForSingleObject(o_Write.hEvent,INFINITE);
           bReadDone = TRUE;
       }
   
       if(bReadDone)
           wcout<<L"I/O Code:"<<o_Write.Internal<<" TransedBytes:"<<o_Write.InternalHigh<<endl;
       else
           wcout<<"Error:"<<::GetLastError()<<endl;
       ::CloseHandle(hFile);
       delete [] pFileContent;
   }

3. 可提醒IO
   

   void Test3()
   {
       //可提醒IO
       HANDLE hFile = ::CreateFile(_T("aaa.txt"),
           GENERIC_WRITE,
           FILE_SHARE_READ,
           NULL,
           OPEN_EXISTING,
           FILE_FLAG_OVERLAPPED,
           NULL);
       if(!hFile)
       {
           wcout<<L"CreateFile Failed ErroCode:"<<::GetLastError()<<endl;
           return ;
       }
       DWORD dwFileSize = ::GetFileSize(hFile,0);
       wcout<<L"FileSize:"<<dwFileSize<<endl;
       LARGE_INTEGER liDis = {0};
       LARGE_INTEGER liRet = {0};
       ::SetFilePointerEx(hFile,liDis,&liRet,FILE_END);
       wcout<<L"PreWrite File Pos:"<<liRet.LowPart<<endl;
       char * pFileContent = new char[10000000];
       memset(pFileContent,‘g‘,10000000);
       DWORD dwReaded = 0;
       OVERLAPPED o_Write = {0};
       o_Write.Offset = liRet.LowPart;
       DWORD bReadDone = ::WriteFileEx(hFile,
           pFileContent,
           10000000,
           &o_Write,
           FileIOCompletionRoutine);
   
       ::CloseHandle(hFile);
       SleepEx(10000,TRUE);
       delete [] pFileContent;
   }

   
   可提醒IO的优劣：
   （1）由于回调函数的原因，最终不得不把大量信息放在全局变量中。使代码变的更加复杂
   （2）发出请求线程和完成处理必须是同一线程，没有达到线程负载均衡
   可提醒IO相关函数
   （1）QueueUserAPC函数
        a.这个函数允许我们手动增加APC项。
        b.可以强制线程退出等待状态比如WaitForSingleObjectEx 以下是示例代码
   

   VOID WINAPI APCFunc(ULONG_PTR pvParam)
   {
       //Nothing To Do
   }
   
   UINT WINAPI ThreadFunc(PVOID pvParam)
   {
       wcout<<L"start Wait...."<<endl;
       DWORD dw = ::WaitForSingleObjectEx(pvParam,INFINITE,TRUE);
       if(dw == WAIT_OBJECT_0)
       {
           wcout<<L"Event signaled"<<endl;
           return 0;
       }
       else if(dw == WAIT_IO_COMPLETION)
       {
           wcout<<L"QueueUserApc Forced us out of a wait state"<<endl;
           return 0;
       }
       return 0;
   }
   void Test4()
   {
       //利用QueueUserApc来停止线程等待
       HANDLE hEvent = ::CreateEvent(NULL,FALSE,FALSE,NULL);
       HANDLE hThread = (HANDLE) _beginthreadex(NULL,0,ThreadFunc,hEvent,0,NULL);
       Sleep(5000);
       QueueUserAPC(APCFunc,hThread,NULL);
       WaitForSingleObject(hThread,INFINITE);
       CloseHandle(hThread);
       CloseHandle(hEvent);
   }

4. I/O完成端口
   待续

异步设备IO 《windows核心编程》第10章学习<待续>