writing nt service using vb6-vb5.htm

VB6实现Windows服务

            way to make the events in Event Viewer show up as the APP name 
            instead of VBRuntime?<BR><SPAN class=A>A:</SPAN> Of course, yes. For 
            example, see the solution in <A 
            href="http://www.fawcette.com/archives/premier/mgznarch/vbpj/2001/09sep01/lj0109/lj0109-1.asp" 
            target=_blank>this article</A>. The code for the article you can 
            download <A 
            href="http://mvps.org/st-software/Code/WriteEventLogsCode_Mod1.zip" 
            target=_blank>here</A>.<BR><BR><SPAN class=Q>Q:</SPAN> I have run 
            the ServiceSampleControl.vbp and installed the service, and then 
            tried starting the service but it didn't not start. When running the 
            ServiceSample.vbp the error states that it must be started as a 
            service.<BR><SPAN class=A>A:</SPAN> Did you try starting 
            SvSampleControl.exe? By this sample design, the service program 
            (SvSample.exe) must be in the same directory as the control program 
            (SvSampleControl.exe) or its project (ServiceSampleControl.vbp), if 
            you prefer starting it in IDE. Because the project of the control 
            program located in the separate directory, the service executable 
            was not found. See System event log - this fact must be reflected 
            there. Of course, this behaviour may be changed by rewriting some 
            bytes in the control program.<BR><BR><SPAN class=Q>Q:</SPAN> Is it 
            possible in to turn on "Allow service to interact with 
            Desktop"?.<BR><SPAN class=A>A:</SPAN> Yes, it is possible. When you 
            call CreateService or ChangeServiceConfig functions, pass this value 
            to dwServiceType parameter: <BR><PRE>SERVICE_WIN32_OWN_PROCESS Or SERVICE_INTERACTIVE_PROCESS

Const SERVICE_WIN32_OWN_PROCESS = &amp;h10&amp;
Const SERVICE_INTERACTIVE_PROCESS = &amp;h100&amp;
</PRE><SPAN class=Q>Q:</SPAN> Is it possible to start a service as 
            another user (administrator) with "Interact with Desktop"?<BR><SPAN 
            class=A>A:</SPAN> No, it is impossible, only LocalSystem services 
            can interact with desktop. It is security feature.<BR>Usually in 
            this situation programmers divide an application into two parts: the 
            service running under some user account with sufficient rights 
            provides main work and network communication; and ordinary 
            auto-start executable provides interaction with current user. These 
            two parts interact each other using one of known methods: COM, named 
            pipes, shared memory etc. Using any of these methods is not simple 
            in conformity with services because they must be modified to 
            overcome security barriers.<BR><BR><SPAN class=Q>Q:</SPAN> Have you 
            noticed any problems with using your service with local DDE 
            application? When that service is running, local DDE application 
            (and some installs written with InstallShield) hang. The process 
            exists on the machine, but the exe does not run. As soon as I issue 
            a STOP to the serivce, the local DDE application begins.<BR><SPAN 
            class=A>A:</SPAN> Try to replace all wait functions 
            (WaitForSingleObject and others) with my non-blocking equivalent 
            function <A 
            href="http://www.smsoft.ru/en/vbwait.htm">MsgWaitObj</A>. Using 
            blocking versions of wait functions in VB program is not correct 
            even if the program have no visible interface (don't touch 
            WaitForSingleObject in NTService.bas: using this function in service 
            thread is lawful, but DoEvents from MsgWaitObj may be not 
            thread-safe, and used there API functions are not declared in type 
            library).<BR><BR>Note: updated source code of service sample is 
            available for downloading, it takes into account above-mentioned 
            considerations.<BR><BR><SPAN class=Q>Q:</SPAN> I want to customize 
            your "NT Service module" application for running my .exe as a NT 
            service. Is there anything I should worry about during 
            customization?<BR><SPAN class=A>A:</SPAN> The first rule for 
            service: it must respond to Stop request as soon as possible. If 
            your program performs long operations, insert intermediate checks 
            for hStopPendingEvent event: <PRE>If WaitForSingleObject(hStopPendingEvent, 0&amp;) = 0&amp; Then ... cancel operation
</PRE>The next rule: initialization code must be brief. That is the 
            program must execute <PRE>SetServiceState SERVICE_RUNNING
</PRE>line within 1-2 seconds.<BR><BR>The sample introduces two 
            different approaches in service design.<BR>1. The program uses 
            objects which respond to external events (for example, you are 
            writing Internet server, which responds to data arrival in socket). 
            You have initialization code, termination code and no code in main 
            loop. The interval for main loop you may set to INFINITE.<BR>2. Your 
            program performs periodic tasks (for example, you are writing time 
            scheduler). You have no initialization code (or very brief 
            assignment initial values for variables at that place), no 
            termination code and all functional code in main loop.<BR>Of course, 
            you may combine these approaches.<BR><BR>The next thing is security. 
            If the service runs in LocalSystem account, it can't access network 
            shares at all, if it runs in some User account, it can access secure 
            objects in accordance with User rights. If your service is COM 
            server, you must use DCOM to access it from user's application even 
            from the same computer. You must add and modify some registry 
            settings to make COM service work properly.<BR><BR><SPAN 
            class=Q>Q:</SPAN> I try to write some value to the registry 
            (HKCU\...) from the service, but registry editor states that nothing 
            was written.<BR><SPAN class=A>A:</SPAN> Your problem is, the service 
            runs in context of another account (typically, "LocalSystem"). That 
            is, HKCU for your interactive session and for service point to 
            different registry hives. Use "HKLM\Software\Your Company\Your 
            Program" key to store data instead. Or start your service in context 
            of your account (it is adjustable in Control 
          Panel\Services).<BR><BR></TD></TR>
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