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.NET Forum / Languages / Managed C++ / July 2005No performance improvement for MultiThreaded call to a VB COM
I have included all the source codes in the attached MyTest.zip (http://www.codeguru.com/forum/attachment.php?attachmentid=11218) There are three projects: VBTestCOM project is a apartment threaded DLL, it has one function doing a stored procedure call. This DLL will be called from C++ multithread. C++ test project is a ATL multithreaded DLL, it just simple created multithread, and call VBTestCom's doSPCall function in each thread. VB client: It set thread number and start a loop calling C++ DLL's Do function. You need created a stored procedure in SQL Server NorthWind database like this: create PROCEDURE dbo.usp_Test AS BEGIN insert Categories(CategoryName,[Description]) values( 'CatName', convert(varchar(30),getdate(),9)) WAITFOR delay '00:00:00.100' end It create a record in Categories and delay 100 milliseconds. In C++ debug, Change the thread number and you will see no performance improvement. Trace time in thread like this: 1 Thread vb function call time: 109 c++ other code time: 62 2 thread vb function call time: 156 c++ other code time: 62 3 thread vb function call time: 256 c++ other code time: 62 It's frustrating! Help! Hi wdwedw! > There are three projects: > VBTestCOM project is a apartment threaded DLL, it has one function doing a [quoted text clipped - 4 lines] > > It's frustrating! Help! If the VBTestCOM project is apartment-threaded (that means: single-threaded) then *all* calls to this COM-object is serialized. So the behaviour is by design. If you want to improve the performance, then switch the VBTestCOM project to both or multi-threaded.  SignatureGreetings Jochen My blog about Win32 and .NET http://blog.kalmbachnet.de/ > Hi wdwedw! > [quoted text clipped - 13 lines] > If you want to improve the performance, then switch the VBTestCOM project > to both or multi-threaded. Which is not possible using VB, VB6 can only produce Single Threaded Apartment (STA) or Single (that is instantiated on the "main apartment") COM DLL's. Willy. This is quite normal, your VB object is a STA object, and you initialize the thread to enter the MTA. The result is that each call as to be marshaled between the MTA and the STA where the object lives, this kill your performance. Initialize your apartment for STA and try again. Willy. >I have included all the source codes in the attached MyTest.zip > (http://www.codeguru.com/forum/attachment.php?attachmentid=11218) [quoted text clipped - 36 lines] > > It's frustrating! Help! Willy, Is that means the VB object can only lives in STA? even though create it from MTA. Is there no ways to improve performannce for VB object with Multithread? What does 'Initialize your apartment for STA' mean and how? Thanks wdwedw > This is quite normal, your VB object is a STA object, and you initialize the > thread to enter the MTA. The result is that each call as to be marshaled [quoted text clipped - 43 lines] > > > > It's frustrating! Help! > Willy, > > Is that means the VB object can only lives in STA? even though > create it from MTA. Is there no ways to improve performannce for VB > object with Multithread? What does 'Initialize your apartment for > STA' mean and how? In your C++ code, for each new thread call CoInitializeEx and pass COINIT_COINIT_APARTMENTTHREADED as the second parameter. That will create a new STA for each thread. A VB-created object can live in any one of those apartments. -cd > Willy, > > Is that means the VB object can only lives in STA? even though create it > from MTA. Is there no ways to improve performannce for VB object with > Multithread? What does 'Initialize your apartment for STA' mean and how? STA objects are single threaded but they can live in multiple STA's and each thread can 'enter' one single STA at a time. Each thread will create/call the object in it's owning STA without the need to marshal and serialize the call, beware that static (shared) variables in your VB COM objects are shared amongst the different thread instances, so their accesses must be synchronized anyway. I've seen many applications using VB COM objects in multithreaded applications breaking because of this thread-unsafe design. Willy. Thanks Carl and Willy. When I created a apartment for each thread, I did see the performance was improved! Two more questions: 1) Is static (shared) variables means public variables in Modules? because they shared in VB project. 2) My ATL object implemented connectionpoint and work fine before, after I create a apartment for each thread and fire the event, I got a First-chance exception during pDispatch->Invoke() in the Fire_ServerFuncDone(LONG nReturn) function. What's wrong? Thanks wdwedw > > Willy, > > [quoted text clipped - 12 lines] > > Willy. I think I got the answer for my second question: I need to fire the event from a different thread: http://support.microsoft.com/kb/q280512/ > Thanks Carl and Willy. > [quoted text clipped - 27 lines] > > > > Willy. Inline Willy. > Thanks Carl and Willy. > [quoted text clipped - 5 lines] > because > they shared in VB project. Exactly. > 2) My ATL object implemented connectionpoint and work fine before, after I > create a apartment for each thread and fire the event, I got a [quoted text clipped - 3 lines] > function. What's wrong? > Thanks So it looks like have a ATL COM object AND a VB6 COM object, this is not what you told us in the initial posting. Who's creating the ATL object instance, who's creating the VB instance what apartments are they in? > wdwedw > [quoted text clipped - 20 lines] >> >> Willy. Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. 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