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    Step 6. Debugging NT Service appication  

As the service is not an ordinary application it`s debugging is complicated enough. Usually to debug the Delphi service application you should start it from the IDE without any switches (I mean installation switches only, of course your application can use it`s own switches if necessary). After it starts you will have 15 seconds (30 seconds are mentioned in other sources) to start the service from the control panel or from the command prompt. Only after these operations the service is considered to be started and you can debug it. To stop it you will have to use the control panel or command prompt again. As for me it is not convenient but you can use this approach to debug the SvCom application too.

But there is another way. Go to the Run|Parameters dialog and enter the /debug switch in the Parameters field.

Debug NT Service

Now start our example from the IDE as you do it with the ordinary applications. The application starts and you see the window that looks like this one:

Main window of NT Service debug utility

Important note: You will need the DebugNTService.dll library to be available via PATH. This library is installed by SvCom setup to the System32 directory by default.

When started with /debug switch the SvCom application does not start as a service. It just emulates the behaviour of the Windows NT Service Control Manager. If you are a registered user you can look into the SvCom_NTService unit to check how it works. After starting in debug mode it calls the debugNTServiceX.dll and cause it to show the service control window. This window shows the status of service and can be used to control it. The caption of this window shows the path of the SvCom application and each page in the multi-page control represents one service of application. In our case there is only one service in it so you will see only one page. The State and Type tabs show the state of service and its configuration respectively. The set of buttons is used to control the service. In addition you will see a small round icon on the tray. The color of icon corresponds to the current service state. The debug window becomes invisible when minimized. Dblclick this tray icon to restore the debug window.

Well, after this brief description you can try to trace our example. Set breakpoints on the OnStart, OnStop event handlers and on the Beep call itself. Press the Start/Continue button and you will see that Delphi debugger stops at the breakpoint in OnStart event handler. Continue execution and the debugger will stop on the Beep call. So, you can trace the SvCom application as an ordinary exe. You can start and stop it as many times as you need and you don`t have 15 seconds time limitations and you don`t have to switch on between Delphi and control panel or command prompt. Finally, you can use this debug mode to start you service application as an ordinary executable! In addition I can say that the nearest SvCom version will support the /autostart switch. Started with /debug and /autostart switches SvCom application starts as ordinary executable and automatically starts all its services. The debug window minimizes itself automatically so you see only icon of the tray. Unfortunately current version of SvCom (1.1) does not support this functionality. Please be patient.

Well, this step finishes the SvCom Example N 1. Continue with next examples to learn more about SvCom.

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