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Q164983: HOWTO: Do Asynchronous WinInet with MFC Classes

Article: Q164983
Product(s): Microsoft C Compiler
Version(s): WINDOWS:4.0; winnt:5.0,6.0
Operating System(s): 
Keyword(s): kbIE400 kbInternet kbMFC kbVC500 kbVC600
Last Modified: 17-MAY-2002

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The information in this article applies to:

- Microsoft Visual C++, 32-bit Enterprise Edition, versions 5.0, 6.0 
- Microsoft Visual C++, 32-bit Professional Edition, versions 5.0, 6.0 
- Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
- Microsoft Internet Explorer (Programming) version 4.0 
- Microsoft Windows Internet Services (WinInet) 
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SUMMARY
=======

The MFC WinInet classes (CInternetSession, CInternetConnection, and so forth)
are not designed to be used with asynchronous WinInet connections or file
transfer. Instead, developers looking for asynchronous-like behavior in their
MFC WinInet application should implement separate synchronous WinInet sessions
in secondary threads.

MORE INFORMATION
================

A WinInet application creates an asynchronous WinInet session by using
INTERNET_FLAG_ASYNC in the last parameter of the CInternetSession constructor,
dwFlags.

Because some Internet operations may take a long period of time to complete, it
is often desirable to make asynchronous WinInet calls, which return control to
the application and run the operation in the background. This allows the
application's user interface to continue to function. In addition, the
application can display status updates on a lengthy download or even allow the
user to halt an operation while it is executing. In this case, the recommended
method for an MFC WinInet application is to not use INTERNET_FLAG_ASYNC in
constructing the CInternetSession. Instead, for each necessary concurrent
session, a secondary thread is spawned from the main thread. Each secondary
thread is responsible for creating a new CInternetSession object without the
INTERNET_FLAG_ASYNC flag and then performing any needed operations on that
synchronous session, such as making an FTP connection and then downloading a
file.

In some cases however, true asynchronous WinInet is really the desired goal. If
this is the case, developers are encouraged to abandon their use of the MFC
WinInet classes and make calls to the WinInet API directly. You can get more
information about this from the Internet Client SDK at:

  http://www.microsoft.com/msdn/sdk/inetsdk/help/default.htm

(c) Microsoft Corporation 1999, All Rights Reserved.
Contributions by Jason Strayer, Microsoft Corporation


Additional query words:

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Keywords          : kbIE400 kbInternet kbMFC kbVC500 kbVC600 
Technology        : kbVCsearch kbIEsearch kbAudDeveloper kbSDKIESearch kbSDKIE400 kbVC500 kbVC600 kbVC32bitSearch kbVC500Search
Version           : WINDOWS:4.0; winnt:5.0,6.0
Issue type        : kbhowto

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