PRB: Internet Explorer 4.0 Keeps Active Document Servers Running
ID: Q177269
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The information in this article applies to:
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Microsoft Internet Explorer (Programming) versions 4.0, 4.01
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Microsoft Visual Basic Professional and Enterprise Editions for Windows, version 5.0
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Microsoft Visual C++, 32-bit Editions, versions 4.2, 5.0
SYMPTOMS
Active Document objects (also known as docobjs, .vbd files, and Active
Documents) are not released upon navigating to a different URL using
Internet Explorer. The server continues running even through several pages
of navigation. This can cause problems for Active Document servers that
expect the last reference to the Active Document object to be released upon
navigating away from the URL that points to the structured storage file.
CAUSE
Internet Explorer 4.0 uses an unexpected way to keep Active Document
servers in memory even after you have navigated away from the URL for the
structured storage file (such as .vbd files). Immediately prior to
releasing the reference to the displayed document, Internet Explorer will
create another (hidden) instance of the Active Document object and hold the
reference to that object for approximately 10 minutes, or when Internet
Explorer exits, whichever comes first.
RESOLUTION
Here is some information for Visual Basic developers:
- Do not use the Terminate event as a notification to shut down your
Active Document server. The Terminate event will be fired once for each
instance of the Active Document objects.
- You will need to exit Internet Explorer while testing your Active
Document server project, rather than simply navigating away from the URL
for the .vbd file.
- Avoid placing code in the UserDocument's Initialize or Terminate event
handlers that should be placed in other event handlers (see MORE
INFORMATION, below).
Here is some information for Visual C++ developers:
- Do not expect the reference count for your docobj server to drop to 0
(zero) when the user navigates away from the structured storage file
associated with your docobj server.
- This behavior mimics the intended behavior of the method
IClassFactory::LockServer(). You should continue to rely upon that
method to keep your server running even if there are no references held
against your objects.
STATUS
This behavior is by design.
NOTE: You should not make software design decisions that rely upon this
behavior. Microsoft reserves the right to change this behavior without
notice at any time.
MORE INFORMATION
There is no specification that requires an Active Document container, such
as Internet Explorer 4.0, to maintain one and only one reference to an
Active Document for each displayed instance. It can create as many
instances as it likes.
Internet Explorer 4.0 uses this additional reference to keep the Active
Document server running. Many Active Document servers, such as the
Microsoft Office suite of applications, take a significant amount of time
to get started. By using this additional reference to the Active Document
object, Internet Explorer 4.0 can keep the server running, thus reducing
the time it takes to display a page that has recently been viewed by the
user.
Internet Explorer 3.x had a four-page "cache," which would hold references
to the current page as well as the last three visited pages. Although
Internet Explorer 4.0 does not have this four-page cache, the latent
reference to the Active Document certainly acts like a cache.
For Visual Basic Developers
Many Visual Basic developers have a tendency to place application startup
and shutdown code in the Initialize and Terminate event handlers,
respectively, of their UserDocument objects. It is extremely likely that
Initialize and Terminate events will overlap each other. In other words,
you cannot rely on a single Terminate event to follow each Initialize event
without other Initialize events in between. This makes the Initialize event
handler a poor place to put code that expects to be fired only once during
the lifetime of the Active Document server.
For instance, the following scenario can be expected to happen most times
while using Internet Explorer 4.0 to view an Active Document:
(... the user navigates to the URL of the VBD file ...)
Sub Main executes (if applicable)
UserDocument1_Initialize event fires (Instance #1)
UserDocument1_InitProperties
-or-
UserDocument1_ReadProperties event fires (Instance #1)
UserDocument1_Show event fires (Instance #1)
(... other events ...)
(... the user navigates to a different URL ...)
UserDocument1_Hide event fires (Instance #1)
UserDocument1_WriteProperties event fires (Instance #1; assumes the
UserDocument.PropertyChanged method is called first)
UserDocument1_Initialize event fires (Instance #2)
UserDocument1_Terminate event fires (Instance #1)
(... 10 minutes elapse, or the user exits Internet Explorer 4 ...)
UserDocument1_Terminate event fires (Instance #2)
(... the application terminates ...)
REFERENCES
Microsoft Windows Platform SDK: COM and ActiveX Object Services; Component Development
- Visual Basic 5.0 Documentation: Component Tools Guide; Creating ActiveX
Components
- Visual C++ Programmer's Guide: Adding Program Functionality; Internet
topics
Additional query words:
DobObj
Keywords : kbActiveX kbIE400 kbIE401 AXSDKDocObjects AXSDKWebBrowser kbIEFAQ
Version : WINDOWS:4.0,4.01,5.0; winnt:4.2,5.0
Platform : WINDOWS winnt
Issue type : kbprb