VB COM, 'DoEvents' inside ActiveX DLL

'DoEvents' inside ActiveX DLL

Author	Message
Tushar Mahapat #1 / 6	'DoEvents' inside ActiveX DLL In objects inside my ActiveX DLL, there are some methods which send a query to the database, then process the results a little, and then return. Would it help peformance to place a 'DoEvents' after fetching results from the database and before processing the results? I have been recently trying to figure out threading with VB and COM, and have seen the injunction for avoiding 'DoEvents' in DLL's, but it is still not clear to me and I need a confirmation. TIA.
Sun, 03 Oct 2004 05:26:58 GMT

#2 / 6	'DoEvents' inside ActiveX DLL
Fri, 19 Jun 1992 00:00:00 GMT

Clive Smit #3 / 6	'DoEvents' inside ActiveX DLL When you say performance, what do you mean? Speed or client interface screen updates (so the mouse is still usable). The former, no, the latter yes. If you go for Doevents (peekMessage) then be circumspect, don't splatter them all over the place, in a big loop you really want to do something like this: For i& = 0 to nLoop-1 ..... 'Do whatever thoust wilt If i& Mod 1000 = 0 Then DoEvents Next i& or explicitly call a screen update if you can e.g. frmMain.refresh or explicitly flash the cursor Screen.mousepointer = vbDefault:screen.mouspointer = vbhourglass to give the user comfort feedback. Use the Mod operator to do this every so many iterations or insert the Doevents/Update statement within an outer loop if the inner loop is big, you could then update an outer loop counter As for within a dll, I've found on a local machine, there shouldn't be problems unless you put Doevents in a stupid place! In some COM components being called you absolutely have to use it in the calling loop (to yield THEIR message loop). Anybody else for better advice re: Doevents in dll's - I'm open to correction here! Quote: > In objects inside my ActiveX DLL, there are some methods which send a > query to the database, then process the results a little, and then > return. Would it help peformance to place a 'DoEvents' after fetching > results from the database and before processing the results? I have > been recently trying to figure out threading with VB and COM, and have > seen the injunction for avoiding 'DoEvents' in DLL's, but it is still > not clear to me and I need a confirmation. TIA.
Sun, 03 Oct 2004 19:57:21 GMT

Tushar Mahapatr #4 / 6	'DoEvents' inside ActiveX DLL Thanks for your response. What I was concerned about was reentrancy. This component will be running on the server and activated by web clients. I was reasoning that since multiple requests would be received to use the DLL, placing a DoEvents just after getting results from the database could free the processor to service another request, thereby aiding performance to some degree. My question was is reentrancy an issue? I was trying to understand the articles at http://search.microsoft.com/gomsuri.asp? n=1&c=rp_Results&siteid=us/dev&target=http://msdn.microsoft .com/library/en- us/vbcon98/html/vbconapartmentmodelmultithreadinginvisualba sic.asp and http://search.microsoft.com/gomsuri.asp? n=2&c=rp_Results&siteid=us/dev&target=http://msdn.microsoft .com/library/en- us/vbcon98/html/vbcondesigningthreadsafedlls.asp. I am using the default model: apartment-threaded. My guess was placing the 'DoEvents' was not going to be harmful. I need a confirmation. TIA. Quote: >-----Original Message----- >When you say performance, what do you mean? Speed or client interface screen Quote: >updates (so the mouse is still usable). > The former, no, the latter yes. >If you go for Doevents (peekMessage) then be circumspect, don't splatter >them all over the place, in a big loop you really want to do something like >this: >For i& = 0 to nLoop-1 > ..... 'Do whatever thoust wilt > If i& Mod 1000 = 0 Then DoEvents >Next i& >or explicitly call a screen update if you can e.g. frmMain.refresh >or explicitly flash the cursor Screen.mousepointer = >vbDefault:screen.mouspointer = vbhourglass to give the user comfort >feedback. Use the Mod operator to do this every so many iterations or insert - Hide quoted text - - Show quoted text - Quote: >the Doevents/Update statement within an outer loop if the inner loop is big, >you could then update an outer loop counter >As for within a dll, I've found on a local machine, there shouldn't be >problems unless you put Doevents in a stupid place! In some COM components >being called you absolutely have to use it in the calling loop (to yield >THEIR message loop). >Anybody else for better advice re: Doevents in dll's - I'm open to >correction here! message >> In objects inside my ActiveX DLL, there are some methods which send a - Hide quoted text - - Show quoted text - Quote: >> query to the database, then process the results a little, and then >> return. Would it help peformance to place a 'DoEvents' after fetching >> results from the database and before processing the results? I have >> been recently trying to figure out threading with VB and COM, and have >> seen the injunction for avoiding 'DoEvents' in DLL's, but it is still >> not clear to me and I need a confirmation. TIA. >.
Sun, 03 Oct 2004 21:20:30 GMT

Clive Smit #5 / 6	'DoEvents' inside ActiveX DLL Despite all I have read, in practice I've not (maybe once or twice in 10 years) had what I unserstood to be re-entrancy problems. I think as I said that if you are reasonably circumspect about how many and where you put them, they are a real boon, to general feel and responsiveness of an app. So maybe we should just suck it and see and maybe also seek really good advice elswhere - Dan Appleman's books and one I rate highly, Advanced Microsoft Visual Basic 6.0 2nd Edition by 'The Mandelbrot Set' (International) Ltd (run by a guy called 'Peet' Morris - its a Microsoft Press book and can be got at agood price from VBUG, the UK's Visual Basic User Group - its by a consortium of programmers from TMS and is real live fantastic in depth analyses of evrything to do with programming in VB. TMS have great reputation at Microsoft I believe, and this book shows why. they design programs from the ground up and the in-house systems to get them built without bugs. Happ hunting, Clive Quote: > Thanks for your response. > What I was concerned about was reentrancy. This component > will be running on the server and activated by web > clients. I was reasoning that since multiple requests > would be received to use the DLL, placing a DoEvents just > after getting results from the database could free the > processor to service another request, thereby aiding > performance to some degree. My question was is reentrancy > an issue? I was trying to understand the articles at > http://search.microsoft.com/gomsuri.asp? > n=1&c=rp_Results&siteid=us/dev&target=http://msdn.microsoft > .com/library/en- > us/vbcon98/html/vbconapartmentmodelmultithreadinginvisualba > sic.asp and http://search.microsoft.com/gomsuri.asp? > n=2&c=rp_Results&siteid=us/dev&target=http://msdn.microsoft > .com/library/en- > us/vbcon98/html/vbcondesigningthreadsafedlls.asp. I am > using the default model: apartment-threaded. My guess was > placing the 'DoEvents' was not going to be harmful. I need > a confirmation. > TIA. > >-----Original Message----- > >When you say performance, what do you mean? Speed or > client interface screen > >updates (so the mouse is still usable). > > The former, no, the latter yes. > >If you go for Doevents (peekMessage) then be circumspect, > don't splatter > >them all over the place, in a big loop you really want to > do something like > >this: > >For i& = 0 to nLoop-1 > > ..... 'Do whatever thoust wilt > > If i& Mod 1000 = 0 Then DoEvents > >Next i& > >or explicitly call a screen update if you can e.g. > frmMain.refresh > >or explicitly flash the cursor Screen.mousepointer = > >vbDefault:screen.mouspointer = vbhourglass to give the > user comfort > >feedback. Use the Mod operator to do this every so many > iterations or insert > >the Doevents/Update statement within an outer loop if the > inner loop is big, > >you could then update an outer loop counter > >As for within a dll, I've found on a local machine, there > shouldn't be > >problems unless you put Doevents in a stupid place! In > some COM components > >being called you absolutely have to use it in the calling > loop (to yield > >THEIR message loop). > >Anybody else for better advice re: Doevents in dll's - > I'm open to > >correction here! > message > >> In objects inside my ActiveX DLL, there are some > methods which send a > >> query to the database, then process the results a > little, and then > >> return. Would it help peformance to place a 'DoEvents' > after fetching > >> results from the database and before processing the > results? I have > >> been recently trying to figure out threading with VB > and COM, and have > >> seen the injunction for avoiding 'DoEvents' in DLL's, > but it is still > >> not clear to me and I need a confirmation. TIA. > >.
Mon, 04 Oct 2004 01:18:36 GMT

Jure Leskove #6 / 6	'DoEvents' inside ActiveX DLL Hi! As I understood, you mixed client requests with VB events. If you look into your asp code, you will see that there is created new instance of your object (createObject("library.class")) for each request from client and they all run independantly. There can be many of the same object running at the same time but you (objects) can't feel it because they all run in their own process. I think there is notrhing wrong using Smith's syntax, but I assume that you don't need it any more. Are you using COM+, 'coz there's a lot of interesting artricles about it. - Jure
Mon, 04 Oct 2004 16:01:03 GMT

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