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Q94954: PRB: DdeInitialize Fails in Implicitly-Loaded DLL’s LibMain()

Article: Q94954
Product(s): Microsoft Windows Software Development Kit
Version(s): WINDOWS:3.1
Operating System(s): 
Keyword(s): kb16bitonly
Last Modified: 06-NOV-1999

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The information in this article applies to:

- Microsoft Windows Software Development Kit (SDK) 3.1 
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SYMPTOMS
========

When implementing DDEML from an implicitly-loaded dynamic-link library (DLL),
calling DdeInitialize() from the DLL's LibMain() function causes the
DdeInitialize() call to fail (that is, results to an exception 13). Moving the
call to DdeInitialize() anywhere other than LibMain() corrects the problem.

CAUSE
=====

In DdeInitialize(), DDEML initializes its data structures, allocates memory, and
also creates windows (for its own internal use). This, of course, causes
messages to be sent to the application's message queue, which at LibMain() time,
in an implicitly-loaded DLL, does not exist yet. These messages sent to a
non-existent message queue result to an exception 13.

RESOLUTION
==========

One way to resolve this problem is to export another function in the DLL, call
it InitDDEML(), which can call DdeInitialize() and perform all necessary
initializations. This guarantees that when the function InitDDEML() is called,
the application's message queue has been properly initialized.

Another way to resolve this problem is to keep the DdeInitialize() call in
LibMain(), but to explicitly load the DLL via LoadLibrary(). This also ensures
that the calling application's message queue exists before the call to
DdeInitialize() in LibMain().

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

Because an implicitly-loaded DLL is loaded into memory before the calling
application is completely loaded, LibMain(), [which is analogous to an
application's WinMain()] is called before the application's message queue is
initialized. As a result, the DLL must not call functions that send messages to
the application in LibMain().

This problem is not specific to DDEML.

Similarly, an implicitly-loaded DLL is terminated after the calling application
has been removed from memory. Therefore, nothing in the Windows exit procedure
(WEP) must require the application to exist.


Additional query words: 3.10 3.1

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Keywords          : kb16bitonly 
Technology        : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK310
Version           : WINDOWS:3.1

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