Re: Multi thread download

From:

"Alexander Grigoriev" <alegr@earthlink.net>

Newsgroups:

microsoft.public.vc.mfc

Date:

Fri, 21 Nov 2008 20:01:17 -0800

Message-ID:

<#OFv5bFTJHA.4372@TK2MSFTNGP04.phx.gbl>

WinInet library may have a restriction (done on purpose) of 2 connections
opened at the same time to the same server... Ever tried downloading
multiple files in IE?

"David" <thuong101277@yahoo.com> wrote in message
news:ORxuW3ETJHA.5688@TK2MSFTNGP03.phx.gbl...

Thank Joseph M. Newcomer very much,

My mean multithread download just from one server and one file, this one
file divide multi segment and query download it in each thread.

"Joseph M. Newcomer" <newcomer@flounder.com> wrote in message
news:p0sdi4thcns20rmj53pde1q0f6gg8ja608@4ax.com...

See below...
On Fri, 21 Nov 2008 16:26:16 +0700, "David" <thuong101277@yahoo.com>
wrote:

hi all,

I want write a programe multi thread downloading use window's functions
such
as: InternetOpen, InternetConnect, HttpOpenRequest, ...etc, but i have
problem query a segment of file from server, i try to add header request
:

****
What do you mean "multithread downloading"? Do you mean many concurrent
downloads from
many different servers, or a multithreaded single download from a single
server?

Note that multithreading will not buy you any performance improvement
because your
bottleneck is the network.
****

strHeader[1024];
_stprintf(strHeader, _T("Range: bytes=%d-\r\n"),dwStartDownload);

if(!::HttpAddRequestHeaders( _hHTTPRequest, strHeader,
_tcslen(strHeader),
HTTP_ADDREQ_FLAG_ADD)){
  ::InternetCloseHandle(_hHTTPRequest);
  ::InternetCloseHandle(_hHTTPConnection);
  ::InternetCloseHandle(_hHTTPSession);
  return false;
}

_stprintf(strHeader, _T("Content-Length: %d\r\n"), dwSegmentSize);

if(!::HttpAddRequestHeaders( _hHTTPRequest, strHeader,
_tcslen(strHeader),
HTTP_ADDREQ_FLAG_ADD)){
  ::InternetCloseHandle(_hHTTPRequest);
  ::InternetCloseHandle(_hHTTPConnection);
  ::InternetCloseHandle(_hHTTPSession);
  return false;
}

DWORD dwFileSizeLocal = 32040848;

****
Was this obtained by the rand() function?
****

  _stprintf(strHeader, _T("Content-Range: bytes %d-%d/%d\r\n"),
dwStartDownload, dwFileSizeLocal, dwFileSizeLocal);

if(!::HttpAddRequestHeaders( _hHTTPRequest, strHeader,
_tcslen(strHeader),
HTTP_ADDREQ_FLAG_ADD)){
  ::InternetCloseHandle(_hHTTPRequest);
  ::InternetCloseHandle(_hHTTPConnection);
  ::InternetCloseHandle(_hHTTPSession);
  return false;
}

//Sending Dwonload Request
if(!::HttpSendRequest( _hHTTPRequest, // handle by returned
HttpOpenRequest
         NULL, // additional HTTP header
          0, // additional HTTP header length
         NULL, // additional data in HTTP Post or HTTP Put
         0 // additional data length
         )){

  ::InternetCloseHandle(_hHTTPRequest);
  ::InternetCloseHandle(_hHTTPConnection);
  ::InternetCloseHandle(_hHTTPSession);

  m_lErrorCode=::GetLastError();

****
If there is a failure, the FIRST thing you do is call ::GetLastError.
Otherwise, the only
error that might be reported is the error that occurred on the last
::InternetCloseHandle.
*****

LPVOID lpMsgBuffer;

****
(a) why is this an LPVOID instead of an LPTSTR? It would save an
unnecessary cast
(b) why is this not a subroutine you call?
****

  DWORD dwRet=FormatMessage( FORMAT_MESSAGE_ALLOCATE_BUFFER |
FORMAT_MESSAGE_FROM_SYSTEM,
                NULL,
                m_lErrorCode,
                MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
                reinterpret_cast<LPTSTR>(&lpMsgBuffer),
                0,
                NULL);
  if(lpMsgBuffer)
   m_sErrorMessage = reinterpret_cast<LPTSTR>(lpMsgBuffer);
  else{
   m_sErrorMessage =_T("Server Request
Exception[CFXProtocolManager::RequestDownload@::HttpSendRequest()");
   m_sErrorMessage.append(_T("@ErrorCode: "));
   TCHAR errCode[__SIZE_SMALL_BUFFER];

****
Why are you declaring a fixed-size buffer for any purpose whatsoever
here?
****

//Convertion::int64ToString(errCode,__SIZE_SMALL_BUFFER,m_lErrorCode);
m_sErrorMessage.append(errCode);
m_sErrorMessage.append(_T("]"));

****
You have not indicated what the type of m_sErrorMessage is; if it is not
CString, why
isn't it? CString does not have an "append" method. If you are using
std::string, why?
It doesn't make sense in MFC programs to use std::string.
****

  }
  LocalFree(lpMsgBuffer);
  if(m_IDownloadListener)

m_IDownloadListener->OnDownloadFinished(SERVER_UNAVAILABLE_CODE,m_sErrorMessage);
  return false;
}

Example i have 3 segment with segment 1, segment 2 i send request ok, but
segment 3 it always fail
Anybody know this problem pls help me, thanks very much.

****
I am curious why you are trying to split a download into three segments.
Do you have any
evidence this improves either the server output rate or the network
bandwidth? Those are
your bottlenecks. This looks like you are creating a complex solution to
a simple
problem.
joe

****

Joseph M. Newcomer [MVP]
email: newcomer@flounder.com
Web: http://www.flounder.com
MVP Tips: http://www.flounder.com/mvp_tips.htm