问题描述
我正在运行Windows 7，但出现ReadFile怪异的行为.
通过指定了FILE_FLAG_OVERLAPPED的CreateFile打开文件并读取*大*的数据块时磁盘(假设500Mb以使效果更明显)，ReadFile最多阻塞10秒钟，然后返回FALSE(GetLastError()报告ERROR_IO_PENDING)，并且我正在*立即*回调异步I/O已完成( BindIoCompletionCallback).这是要复制的代码:
(我剥离了IOCP绑定以削减代码，这两种方式都可以复制)
//打开文件
HANDLE hFile = CreateFileW(L"c:\\ path \ to \ large \ file"，GENERIC_READ，0，NULL，OPEN_EXISTING，FILE_FLAG_OVERLAPPED，NULL);
I'm running Windows 7 and I'm getting weird behavior of ReadFile.
When opening a file via CreateFile with FILE_FLAG_OVERLAPPED specified, and reading a *large* chunk of data off the disk (let's say 500Mb to make the effect more noticeable), ReadFile blocks for up to 10 seconds, then returns FALSE (GetLastError() reports ERROR_IO_PENDING) and I'm getting *immediate* callback that async I/O is complete (BindIoCompletionCallback). Here is a code to reproduce:
(I stripped IOCP binding to cut down the code, it is reproducible both ways)
// open file
HANDLE hFile = CreateFileW(L"c:\\path\to\large\file", GENERIC_READ, 0, NULL, OPEN_EXISTING, FILE_FLAG_OVERLAPPED, NULL);
int dataSize = 500 * 1024 * 1024;
char * data =(char *)malloc(dataSize);
memset(data，0xFF，dataSize); //预热，以便请求整个内存
重叠；
内存集(& lapd，0，sizeof(overlapped));
printf ("reading ... \ n"); fflush(stdout);
BOOL结果= ReadFile(hFile，data，dataSize，NULL和重叠)； //这里最多延迟10秒
printf("done！\ n"); fflush(stdout);
printf(结果:％d GetLastError():％d \ n"，结果是GetLastError()); fflush(stdout);
DWORD bytesRead;
结果= GetOverlappedResult(hFile，&重叠，& bytesRead，TRUE); //等待完成-立即返回
printf(读取的字节:％d \ n"，bytesRead);&ffbff(stdout);
CloseHandle(hFile );
我是不是在做一些愚蠢的错误，这是故意的(高度怀疑)，还是它的错误?
我不打算在XP上对此进行测试.
int dataSize = 500 * 1024 * 1024;
char* data = (char*)malloc(dataSize);
memset(data, 0xFF, dataSize); // warm-up so that the whole memory is requested
OVERLAPPED overlapped;
memset(&overlapped, 0, sizeof(overlapped));
printf("reading...\n"); fflush(stdout);
BOOL result = ReadFile(hFile, data, dataSize, NULL, &overlapped); // up to 10 seconds delay here
printf("done!\n"); fflush(stdout);
printf("Result: %d GetLastError(): %d\n", result, GetLastError()); fflush(stdout);
DWORD bytesRead;
result = GetOverlappedResult(hFile, &overlapped, &bytesRead, TRUE); // wait until completion - returns immediately
printf("Bytes read: %d\n", bytesRead); fflush(stdout);
CloseHandle(hFile);
Am I doing something stupid wrong, is this intended (highly doubt that), or is it a bug?
I'm off testing this on XP. BRB!
推荐答案
这篇关于ReadFile始终会阻塞直到读取完成，即使对于异步操作也是如此的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！