BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  How do I build a truly singleton COM server serving multiple          BorlandTalk.com Forum Index -> C++ Builder (ActiveX) View previous topic :: View next topic   Author Message Alan Bellingham Guest Posted: Mon Jul 25, 2005 11:02 am    Post subject: How do I build a truly singleton COM server serving multiple I have an out-of-process EXE server designed to run as a single instance server. (Yes, I know, singletons bad. Except that in this case, it truly models a singleton resource. In this case, it's a specialised printer queue manager, one queue per available printer, one manager for the whole lot. The manager is the unavoidable singleton.) This server should run as a singleton for the entire system. In fact, it's not. Any number of COM instances may be started by user programs, or any number of COM instances may be started by ISAPI, and all is fine. But if both ISAPI and a user program attempt to instantiate COM objects, then multiple instances of the COM server are started. (I can tell this, because I have a Mutex that prevents multiple instances running, and this mutex is indeed preventing a second instance running in this case.) So, how do I serve both a web server (running as a service) and a user program with a single instance of a COM server? Do I have to build it as a service? Alan Bellingham -- ACCU Conference 2006 - 19-22 April, Randolph Hotel, Oxford, UK Back to top Remy Lebeau (TeamB) Guest Posted: Mon Jul 25, 2005 4:29 pm    Post subject: Re: How do I build a truly singleton COM server serving mult "Alan Bellingham" <alanb (AT) episys (DOT) com> wrote Quote: Yes, I know, singletons bad. Says who? Quote: This server should run as a singleton for the entire system. In fact, it's not. Any number of COM instances may be started by user programs, or any number of COM instances may be started by ISAPI, and all is fine. Yes, that is fine. Quote: But if both ISAPI and a user program attempt to instantiate COM objects, then multiple instances of the COM server are started. (I can tell this, because I have a Mutex that prevents multiple instances running, and this mutex is indeed preventing a second instance running in this case.) If you mean the actual EXE is being executed multiple times, then it sounds like you did not set up the EXE properly in the first place. What are the EXACT steps you took to design the EXE and its settings? Quote: Do I have to build it as a service? I would suggest that anyway. Gambit Back to top Alan Bellingham Guest Posted: Mon Jul 25, 2005 5:28 pm    Post subject: Re: How do I build a truly singleton COM server serving mult "Remy Lebeau (TeamB)" <no.spam (AT) no (DOT) spam.com> wrote: Quote: "Alan Bellingham" <alanb (AT) episys (DOT) com> wrote in message Yes, I know, singletons bad. Says who? Quite a lot of design commentators. Actually, it's not quite the 'GOTO considered Harmful' of the Patterns world, but it's close. There are times when singletons are the correct solution, just fewer than they actually get used for. But this is beside the point. Quote: But if both ISAPI and a user program attempt to instantiate COM objects, then multiple instances of the COM server are started. (I can tell this, because I have a Mutex that prevents multiple instances running, and this mutex is indeed preventing a second instance running in this case.) If you mean the actual EXE is being executed multiple times, then it sounds like you did not set up the EXE properly in the first place. What are the EXACT steps you took to design the EXE and its settings? Indeed, the EXE is getting executed multiple times and indeed, this is not what is wanted. As to the steps to design the EXE and its settings ... well, once upon a time back in 1991 ... The design history is a real case of bolting code on here, ripping it out there, and so on. In this case, what was once a GUI program has now had all the UI ripped off it (and turned into a different program), and COM interfaces added instead. It works very nicely, excluding the problem in question. Implementation was achieved by wizard building a bare EXE COM server (in Visual C++ 6), and then taking the relevant parts and pasting them into the existing code. Ah, it's built using ATL, if that may make a difference, with a CComModule descendant. (I've had very bad experiences with the BCB3/5 VCL com support.) Do you know of any suitable skeleton example that I could rip apart and try, rather than try to produce a <50 line example? Either that, or any on-line tutorial or previous discussion of similar issues? (Yes, I've tried Googling.) Quote: Do I have to build it as a service? I would suggest that anyway. Ah. I was hoping to avoid having to do that, though I also do suspect it would make the problem go away. Alan Bellingham -- ACCU Conference 2006 - 19-22 April, Randolph Hotel, Oxford, UK Back to top Remy Lebeau (TeamB) Guest Posted: Mon Jul 25, 2005 8:07 pm    Post subject: Re: How do I build a truly singleton COM server serving mult "Alan Bellingham" <alanb (AT) episys (DOT) com> wrote Quote: As to the steps to design the EXE and its settings ... well, once upon a time back in 1991 ... I don't need the whole history. I just wanted you to explain, in detail, everything you did after "File | New" to begin the COM project. Quote: Implementation was achieved by wizard building a bare EXE COM server (in Visual C++ 6), and then taking the relevant parts and pasting them into the existing code. Why did you not use BCB's own wizards to create a COM project? You should have. You are likely missing some compiler/linker options for the EXE. Create a new EXE using BCB's wizard, then use BCB's wizards to add a Type Library and an Automation Object to the project. Then go into the Project Options and set up the ATL options as needed. Quote: I've had very bad experiences with the BCB3/5 VCL com support. What kind of problems? Quote: Ah. I was hoping to avoid having to do that Why? 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