Why does Internet Explorer not call DLL_PROCESS_DETACH on my DLL when I call ExitProcess?

Raymond Chen


A customer asked a question,
but as is often the case,
the question was much more telling than the answer.

We have an Internet Explorer plug-in which calls
to force Internet Explorer to exit.
We found that when we do this, our plug-in does not receive a
DLL_PROCESS_DETACH notification.
What could be preventing our plug-in from receiving the
DLL_PROCESS_DETACH notification?

As we saw some time ago when we looked at

the way processes shut down


an important follow-up

or two
all a process has to do to thwart proper delivery of
DLL_PROCESS_DETACH notifications is to do something
untoward during shutdown, at which point the kernel

just gives up and calls Terminate­Process

But like I said, the answer is much less interesting than the question.
What if the user had an unsaved email message at the time you decided
to exit Internet Explorer?
Recall that

plug-ins are a guest in the host process; don’t go changing the carpet
When we asked the customer why they were exiting Internet Explorer from
their plug-in, we received the explanation,
“The reason I am calling Exit­Process
is that I do not know another good way to exit Internet Explorer
from a plug-in.”

In this case, the guest is doing far more than just changing
the carpet.
The guest called in a

demolition company

“Why did you call the demolition company to destroy my house?”
“I couldn’t think of a good way to destroy your house.”

The point isn’t that it’s bad to use a telephone call to hire a demolition
company to destroy somebody’s house and that you should use some other
method to contact them (like, say, a text message).
The point is that
it’s bad to destroy somebody else’s house in the first place.

Upon further investigation, the customer was writing a test
for their plug-in.
They open Internet Explorer and navigate to a page that uses
the plug-in.
When they are satisfied that the plug-in operated correctly,
they want to exit the copy of Internet Explorer in order to conclude
the test.

If you want to destroy a house, then destroy your own house.
to build a house,
navigate to your test page with
and when you’re done, you can destroy the house with

There is sample code to do exactly this in the documentation for
the IWeb­Browser2 interface

Bonus chatter:
The IWeb­Browser2 interface is scriptable.

var ie = new ActiveXObject("InternetExplorer.Application");
ie.Visible = true;
WScript.Sleep(5000); // five seconds, say
Raymond Chen
Raymond Chen

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