Re: multi-process singleton DLL

From:
"Alex Blekhman" <tkfx.REMOVE@yahoo.com>
Newsgroups:
microsoft.public.vc.language
Date:
Mon, 23 Jul 2007 21:30:54 +0300
Message-ID:
<eU86beVzHHA.1484@TK2MSFTNGP06.phx.gbl>
"PaulH" wrote:

Instead of using IPC, wouldn't it be possible to use
DuplicateHandle()
such that ProcessA opens the DLL and gets the original
resource
handle, then Process B opens the DLL and gets a
DuplicateHandle()?


You will need IPC in any case. In order to use
`DuplicateHandle' in ProcessB you will need to communicate
source handle from ProcessA.

I'm glad you mentioned the second process. I didn't
consider what
would happen to Process B if Process A closed the
resource. What about
using the DLL to keep a reference count of all the handles
created,
then it could wait for the reference to become 0 before it
really
releases the resource. Would that work?


No, it wouldn't. DLL cannot count or wait. It is just a
chunk of executable code, which is loaded into a process.
Think about it as of text file. Suppose you open the same
text file with two instances of Notepad. Now each Notepad
has its own copy of text in memory. You can do whatever you
want with the text in one Notepad, but it won't change the
text in the other one.

If the resource you want to share is kernel object, then it
will stay alive until there is a handle to it. It is not
important which process will contain the handle.

Alex

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