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The normal way to solve such a problem is simply to marshal a pointer to the receiving COM object to the senders apartment and then the sender can simply call a method on the receiver (really the receiver’s proxy) and push the data at it - There is no need for pipes and the like.
Steve
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Sure, that's fine if you have a finite amount of data transfered synchronously from object 1 to object 2.
But what if object 1 is pumping out an infinite (or at least, indefinitely large) stream of data, say in 100 byte chunks, one chunk every 100usec, and I want object 2 to be able to process the stream of data at a slower rate (e.g. 1000 chunks every 100msec, or whenever object 2 gets a chance)?
(think of MP3 or video streaming, though in my case the application is completely different)
--Jason
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In that case the receiver could simply queue the data and not process it immediately. The sender could call CoTaskMemAlloc to get some memory and fill it, then call the method on the receiver’s proxy and give it the memory block. The receiver would stash the address of this memory block in a queue. When the receiver gets around to it would process it and free the block by calling CoTaskMemFree.
Steve
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right, but then I have to take an RPC call every time the sender wants to send something. This is awful expensive. And at a source rate of 1 chunk every 100usec, it essentially won't work unless the two objects live in the same apartment. Some informal experiments seem to indicate inter-apartment calls on my CPU take between 100us and 1msec depending on how much data is marshalled. Actually in a lot of cases my chunk size might be 10 or 20 bytes every 100usec, so there's a tremendous amount of overhead here for the data rate.
I've thought of having the sender batch it up into larger chunks arriving slower & doing essentially what you're talking about, having the receiver queue things explicitly (which is what I'm doing now to get around the problem), but that's a bit kludgy. The major downsides in my application are that [a] my object's clients have to know about & manage the batch-processing (not that bad, but nevertheless a pain) and [b] if the sender dies before it finishes a batch, I lose the chunks that the sender had queued up in the partially-stored batch. This is a datalogging application & I need to lose as little data as possible. (especially if the last bits of data would tell me something about the cause of the sender's death; the sender program may be getting this data from an unreliable program which could cause it to crash. yes I know programs shouldn't crash but sometimes they do, especially if they're not mine  )
If I were to use a pipe (and I'm implementing both objects so they could, theoretically use out-of-band methods to talk to each other, though I'd rather not), the CPU overhead seems like it would go way down (admittedly, haven't tried it yet), and everything that the sender sticks into the pipe before it dies should eventually arrive at the receiver (even if the receiver takes a bit of time to get around to reading from the pipe).
Summary: I care about throughput, not latency, and the # of method calls through standard COM eats into my throughput too much, so I was hoping there would be a pipe for me to stuff bytes into. These are really bytes, they're not interface pointers or BSTR's or anything. (Or if they do mean something, they're handled at my application level.)
--Jason
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In the scheme I described earlier using CoTaskMemAlloc you only send the address of the memory block and perhaps its size - Not 20 bytes. That said, if you want to use pipes the only real problem is getting the handles to the pipes to the sender and receiver. You could use CreapeNamesPipe and transmit the name of the pipe.
Steve
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If you are interested in getting the highest performance, I would think that a memory mapped file like this would produce the highest performance:
http://www.codeproject.com/threads/XQueue.asp[^]
Using the GridView is like trying to explain to someone else how to move a third person's hands in order to tie your shoelaces for you.
-Chris Maunder
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Hi,
I'm trying to create a multiple instance of the same ActiveX(OCX)objects from a container application(Dialog). The problem is that the multiple instance of each object share the same process. Is there a way to create the objects per process?
Thanks
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Anthony9887 wrote: The problem is that the multiple instance of each object share the same process.
Of course, that's part of the whole idea with an ActiveX control since an ActiveX control is in fact a DLL encapsulating with one or more COM objects with automation interfaces and usually a GUI.
Anthony9887 wrote: Is there a way to create the objects per process?
Why? It doesn't make sense.
It would be like being forced to start Word to be able to perform a spell check in Outlook.
What are you trying to do and how can the above be a problem?
--
Roger
It's supposed to be hard, otherwise anybody could do it!
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Hi Roger,
I have a custom server(OCX) which samples data from a D/A hardware through a container application. I want to be able to have 1 container application, that have many server objects sampling data from multiple hardware. When I create the first instance of the server object, it connects and samples, when I create the instance of the second server object, it connects, but the previous object is no longer sampling. When I call a method from the first server object to start sampling, the second object begins sampling. I'm a little confused? Any ideas?
Regards,
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I don't know what kind of hardware you're using or how your server is implemented.
However, I suspect the server to some kind of functionality to be able to select which hardware to use where you provide an index or some string to identify the hardware, e.g. "COM1". Otherwise you would not be able to use multiple hardware, which may actually be the fact, in theory, if the server is badly designed.
Regarding the fact that your first instance of the server stops sampling when you create a second server could mean a lot of things. One could be that both servers are using the same hardware because both servers use some kind of default hardware index or similar.
Without more information about your server's interface at least, it's not possible to help you further. Besides from guessing about how it should work...
Code snippets of how you create your server and what hardware you're using would be nice, as well.
--
Roger
It's supposed to be hard, otherwise anybody could do it!
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Hi Roger,
I think I found the problem. I have global pointer to the Server Object class and this global pointer points to this object during creation. Whenever I create a new instance of the Server object, the global pointer is re-assigned and pointed to the new object. How can I avoid this? Is there a way not to make the pointer global. I do need access to the Server Object via this pointer.
Thanks
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Is creating an Office COM addin using ATL with Late Binding possible? Most of the examples in CodeProject use Early Binding. Using #import to import the libraries means that Early Binding is used, isn't it?
Well, I want to create an ATL Office Addin but with Late Binding. Is this possible? If possible, could anyone guide me.
Thanks. 
---
With best regards,
A Manchester United Fan
The Genius of a true fool is that he can mess up a foolproof plan!
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I don't clear what you want but i think you wanna to load the addin when you want it
in the addin .rgs file we have the addin dll registration having option LoadBehavior where you can specify your possible loading behaviors
Regards
Laxman
Knock out "T" from CAN'T
You 'CAN' if you think you 'CAN'
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Greetings,
I am building a VB.NET dll to respond to the click event of a custom button added to IE's toolbar. In response to the button click the .dll will print the current page to a specific printer without the user needing to choose it from the print dialog.
I am implementing the IObjectWithSite interface to handle acquiring a reference to the browser. And I am implementing the IOLECommandTarget interface in order to receive the click notification via the Exec method.
If I set up the registry entries under "Browser Helper Objects" my .dll is being properly instantiated by IE when it loads, and I am successfully acquiring a reference to the browser with "wb = CType(pUnkSite, SHDocVw.IWebBroswer2)" in the SetSite method of IObjectWithSite.
However, upon clicking the custom toolbar button, the SetSite method is apparently called again, and I encounter the following error when attempting to acquire the broswer reference:
Unable to cast COM object of type 'System.__ComObject' to interface type 'SHDocVw.IWebBrowser2'. This operation failed because the QueryInterface call on the COM component for the interface with IID '{D30C1661-CDAF-11D0-8A3E-00C04FC9E26E}' failed due to the following error: No such interface supported (Exception from HRESULT: 0x80004002 (E_NOINTERFACE)).
Any ideas on why this is happening?
Thanks
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I use CoCreateInstance(...) to create an instance of a COM/ATL DLL that I wrote, then use obj->Release() when done with it. During development I discover the only way to remove it from memory is to reboot! Is there a better way? I cannot replace the dll when its in use.
thanks
-- modified at 14:08 Wednesday 29th March, 2006
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Thanks -- just what I was looking for 
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Can anyone explain what the macro _COM_SMARTPTR_TYPEDEF does? 
---
With best regards,
A Manchester United Fan
The Genius of a true fool is that he can mess up a foolproof plan!
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When you declare a code like below or when compiler generates such a code for you because of the #import statement:
_COM_SMARTPTR_TYPEDEF(ICustomInterface, __uuidof(ICustomInterface));
Compiler will expand this macro _COM_SMARTPTR_TYPEDEF into:
typedef _com_ptr_t<_com_IIID<ICustomInterface, __uuidof(ICustomInterface)> > ICustomInterfacePtr;
Then in Ur code u can use ICustomInterfacePtr as
ICustomInterfacePtr pICustomInterface(__uuidof(CustomInterface) ); // where CustomInterface is the CoClassname for ICustomInterface.
This pICustomInterface is equivalent of ICustomInterface* with the added advantage of auto addref and release. You don’t have to bother anything about the IUnknown method invocations for ICustomInterface*
cheers...mil10.
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Thanks!
---
With best regards,
A Manchester United Fan
The Genius of a true fool is that he can mess up a foolproof plan!
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Hello!
A little question: how to construct(or attach to) ActiveX Control wrapper class, derived from CWnd, already exist COM object presented with LPDISPATCH.
-- modified at 14:29 Tuesday 28th March, 2006
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hi all
Following error occur in my atl com project.this project is using both the atl and mfc classes.Tool is visual studio 2003.
d:\Microsoft Visual Studio .NET\Vc7\atlmfc\include\atlcom.h(1759): error C2259: 'ATL::CComObject<base />' : cannot instantiate abstract class
with
[
Base=CMakeBarcode
]
Tasleem arif
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I think the error has to do with implementing all the virtual functions etc. So I would suggest:
Make sure you are implementing all the virtual methods of the base class. Also make sure that the function signatures are exactly the same.
Could you post some of the relevant "Output" from the compilation. That could tell us what the error is.
this is this.
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Hi,
I am working on Media File Steam Edition, and want to cut a file into many, and join two files. I am using DirecX9 SDK. I tried hard, but cant go on further with my own knowledge.
Can any knowledged person guide me for the same. I was working on .avi files, but now am thinking of .wmv files.
Any thing that can help me do the coding for joining and cutting media files will do.
Thanks,
Jc Shreyash Singh Parihar
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CComObject::CreateInstance method creates new instance of CComObject<class>. Instead I want to access running instance of class, if there is any. Is it possible?
-- modified at 5:48 Tuesday 28th March, 2006
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