OVERLAPPED I/O 异步APC

APC简介:APC

附: 套接字中的WSAOVERLAPPED 和 OVERLAPPED 是一个东西.

OVERLAPPED 中的InternalHigh 用于显示当前读取了多少字节. Internal 用于显示错误信息, 0 即无错误;

GetOverlappedResult 返回的字节以及错误都是根据 OVERLAPPED 结构中的字段来提取的.

这也是为什么GetOverlappedResult 需要的OVERLAPPED结构是一开始初始化的那个

同时也是为什么每个io操作都需要唯一一份OVERLAPPED.

注意: 如果想要复用OVERLAPPED结构(即在一次操作完成之后) . 一定要memset OVERLAPPED ,让其内部清0 .因为内部还

残留上一次操作的记录;

第一个例子. 第二个例子使用APC 来解决一些问题

/*首先使用 OVERLAPPED  结构, 其中有Event 对象, 可用可不用,这个例子先不用CreateFile 其中一个参数使用 FILE_FLAG_OVERLAPPED ReadFile  默认同步, 在最后一个参数使用 OVERLAPPED  ;ReadFile  返回TRUE ，则代表已经读完了否则应该检查 GetLastError , 系统是否为此安排了等待.如果 GetLastError == ERROR_IO_PENDING ,则成功了, 等着取数据, 否则失败之后可以使用 GetOverlappedResult(最后一个参数为TRUE) / WaitForSingObject 来等待直到完成;*/void read_overlapped(const TCHAR * path)
{//这里没有使用其中的 Event 对象. OVERLAPPED overlap = {0};DWORD bytesReaded = 0;BOOL ret = FALSE;char * buf = new char[8196 * 10];// 注意:FILE_FLAG_OVERLAPPED HANDLE hFile = CreateFile(path,GENERIC_READ,FILE_SHARE_READ,0,OPEN_EXISTING,FILE_FLAG_OVERLAPPED,NULL);if(INVALID_HANDLE_VALUE == hFile){cout << "INVALID_HANDLE_VALUE" << endl;return;}//从哪开始读文件 overlap.Offset = 0;//注意overlap 需要传入ret = ReadFile(hFile,buf,8196*10,&bytesReaded,&overlap);//直接就完成了, 您的计算机硬盘可真快if(ret){cout << "done :" <<  bytesReaded << endl;cout << buf << endl;}else{//检测一下错误, 确认是否已经进入准备状态DWORD err = GetLastError();//okif(ERROR_IO_PENDING == err ){//GetOverlappedResult(hFile,&overlap,&bytesReaded,TRUE); 相当于WaitForSingObject//这样其实不太好 , 浪费cpu.while(1){cout << "LOADing: " << GetLastError() << endl;ret = GetOverlappedResult(hFile,&overlap,&bytesReaded,FALSE);if(ret){cout << "ret:" << ret << ",bytesread:" << bytesReaded << endl;break;}}}else{cout << "err : " << err << endl;}}CloseHandle(hFile);
}

通过OVERLAPPED 中的事件对象,对同一个文件读取多次 .

void read_overlapped2(const TCHAR * path)
{HANDLE event_handles[2];OVERLAPPED overlap[2] = {0};char * buf[2] = {0};DWORD  num = 0;HANDLE hFile = CreateFile(path,GENERIC_READ,FILE_SHARE_READ,0,OPEN_EXISTING,FILE_FLAG_OVERLAPPED,NULL);if(INVALID_HANDLE_VALUE == hFile){cout << "INVALID_HANDLE_VALUE" << endl;return;}BOOL ret = 0;int success_len = 0;for(int i = 0; i < 2; ++i){event_handles[i] = CreateEvent(0,TRUE,FALSE,NULL);overlap[i].hEvent = event_handles[i];overlap[i].Offset = i*1000 + i;buf[i] = new char[8196 * 1024];ret = ReadFile(hFile,buf[i],8196 +overlap[i].Offset  ,&num,&overlap[i]);if(ret){cout << "index:" << i << ", is done" << endl;cout << "index:" << i << ",num:" << num;cout << "index:" << i << buf[i] << endl;++success_len;}else {if(GetLastError() != ERROR_IO_PENDING){cout << "index:" << i << "failed" << endl;delete[] buf[i];SetEvent(event_handles[i]);}else {++success_len;}}}cout << "success_len:" << success_len << endl;WaitForMultipleObjects(success_len,event_handles,TRUE,-1);ret = GetOverlappedResult(hFile,&overlap[0],&num,FALSE);cout << "ret:" << ret << ", num:" << num << endl;ret = GetOverlappedResult(hFile,&overlap[1],&num,FALSE);cout << "ret:" << ret << ", num:" << num << endl;CloseHandle(hFile);}

使用ReadFileEx APC:

const int count = 2;
HANDLE event_io;
void CALLBACK ioCompletionRoutine(_In_    DWORD        dwErrorCode,_In_    DWORD        dwNumberOfBytesTransfered,_Inout_ LPOVERLAPPED lpOverlapped)
{int index = (int)lpOverlapped->hEvent;printf("index : %d , readbytes: %d ,err:%d\n", index, dwNumberOfBytesTransfered, dwErrorCode);if (++index == count){SetEvent(event_io);}
}void test_readfileex(const TCHAR * path)
{event_io = CreateEvent(0, TRUE, FALSE, 0);const int bufsize = 2 << 13;HANDLE hFile =CreateFile(path, GENERIC_READ, FILE_SHARE_READ | FILE_SHARE_WRITE, NULL, OPEN_EXISTING,FILE_FLAG_OVERLAPPED, NULL);if (INVALID_HANDLE_VALUE == hFile){printf("createfile failed");return;}OVERLAPPED overlap[count] = { 0 };TCHAR* buf[count] = { 0 };DWORD ret = 0 , err = 0;for (int i = 0; i <count; ++i){overlap[i].hEvent = (HANDLE)i;overlap[i].Offset = i *bufsize + i;buf[i] = new TCHAR[bufsize];ret = ReadFileEx(hFile, buf[i], bufsize, &overlap[i], ioCompletionRoutine);err = GetLastError();printf("ret:%d, err:%d\n", ret, err);if (!ret){// 出错了 }}while (1){ //注意是带ex结尾的 . 这里将阻塞ioCompletionRoutine 完成后将返回一次,所以需要判断ret = WaitForSingleObjectEx(event_io, -1, TRUE);if (WAIT_OBJECT_0 == ret)break;elseprintf("WaitForSingleObjectEx return :%d\n", ret);}CloseHandle(hFile);CloseHandle(event_io);for (int i = 0; i < count; ++i)delete[] buf[i];
}

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