mingw32: Open file using _wsopen and added --enable-mmap support

I tried CreateFile but the subsequent ReadFile fails with Access
Denied if sparse file is read on NTFS. I mostly reverted previous
changes and use _wsopen with read/write share enabled instead of
CreateFile.

This change also includes --enable-mmap support for MinGW32
build. Memory mapped file may be useful for 64-bits OS and lots of
RAM. Currently, FlushViewOfFile is not called during the download, so
it is slightly vulnerable against sudden power loss. I found lots of
read when resuming download due to page fault. So for now it is useful
for the initial download. I recommend not to use
--file-allocation=prealloc with --enable-mmap for MinGW32, because it
triggers page faults even in the initial download. Anyway, the option
is experimental.

1 files changed, 7 insertions, 4 deletions

diff --git a/src/AbstractDiskWriter.h b/src/AbstractDiskWriter.h
index 282aaffd..34eabadd 100644
--- a/src/AbstractDiskWriter.h
+++ b/src/AbstractDiskWriter.h
@@ -44,15 +44,18 @@ class AbstractDiskWriter : public DiskWriter {
 private:
   std::string filename_;
 
-#ifdef __MINGW32__
-  HANDLE fd_;
-#else // !__MINGW32__
   int fd_;
-#endif // !__MINGW32__
 
   bool readOnly_;
 
   bool enableMmap_;
+#ifdef __MINGW32__
+  // This handle is retrieved from fd_ using _get_osfhandle(). It is
+  // used for Win32 API functions which only accept HANDLE.
+  HANDLE hn_;
+  // The handle for memory mapped file. mmap equivalent in Windows.
+  HANDLE mapView_;
+#endif // __MINGW32__
   unsigned char* mapaddr_;
   int64_t maplen_;