PRB: DdeInitialize Fails in Implicitly-Loaded DLL's LibMain() (94954)
The information in this article applies to:
- Microsoft Windows Software Development Kit (SDK) 3.1
This article was previously published under Q94954 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.
Modification Type: | Minor | Last Reviewed: | 2/24/2004 |
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Keywords: | kb16bitonly KB94954 |
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