KnowledgeBase Archive

An Archive of Early Microsoft KnowledgeBase Articles

View on GitHub

Q177917: Initializing a DLL Using DLLMain Optional Entry Point

Article: Q177917
Product(s): Microsoft Windows NT
Version(s): WinNT:4.0
Operating System(s): 
Keyword(s): kbnetwork kbAPI kbRPC kbSDKPlatform kbGrpDSNet
Last Modified: 09-AUG-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft Windows NT Workstation version 4.0 
- Microsoft Windows NT Server version 4.0 
-------------------------------------------------------------------------------

SUMMARY
=======

In Win32, all dynamic link libraries (DLLs) may contain an optional entry- point
function (usually called DllMain) that is called for both initialization and
termination. This gives you an opportunity to allocate or release additional
resources as needed. Windows calls the entry-point function in four situations:
process attach, process detach, thread attach, and thread detach.

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

The DllEntryPoint function is an optional method of entry into a DLL. If the
function is used, it is called by the system when processes and threads are
initialized and terminated, or upon calls to the LoadLibrary and FreeLibrary
functions.

The body of your DLL entry-point function should perform only simple
initialization tasks, such as setting up thread local storage (TLS), creating
synchronization objects, and opening files. You must not call LoadLibrary in the
entry-point function, because you may create dependency loops in the DLL load
order. This can result in a DLL being used before the system has carried out its
initialization code.

Calling Windows functions other than TLS, synchronization, and file functions may
result in problems that are difficult to diagnose. For example, calling User,
Shell, COM, RPC, and Windows Sockets functions (or any functions that call these
functions) can cause access violation errors, because their DLLs call
LoadLibrary to load other system components.

======================================================================
Keywords          : kbnetwork kbAPI kbRPC kbSDKPlatform kbGrpDSNet 
Technology        : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT400search kbWinNTSsearch kbWinNTS400search kbWinNTS400
Version           : WinNT:4.0
Issue type        : kbinfo

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.