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timed polling of a database in a W2K service

Posted on 2002-03-31
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Last Modified: 2010-04-02
Using the ATL Wizard in VC++6 I've created a service.  I'm guessing that my code has to go in the run() method.

My first question is:

If all I want my service to do is after a set time interval get some data from the database.  How do I loop?
If I put a while loop in the run method then i will effectively lock the service from communicating with the SCM.

Any help or small examples would be great, I do have a book on it but as of yet I've not found anything regarding this, and I am pushed for time.

Second question:
Can ATL system services support MFC class usage?
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Question by:MattC
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Accepted Solution

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cookre earned 150 total points
ID: 6909448
There are several ways:
Use a timer to activate a function at a specified interval:


#define    MonitorID 1
UINT       MonitorTimer;

MonitorTimer=SetTimer(hWnd
                     ,MonitorID
                     ,10000     // (10 second interval)
                     ,(TIMERPROC)NSEMonitor);


void CALLBACK NSEMonitor(HWND hwnd
                        ,UINT uMsg
                        ,UINT_PTR idEvent
                        ,DWORD dwTime)
With this method, your program can go about others chores and the call back proc will be triggered at the specified intervals.



The other way is with a simple Sleep():

Sleep(2000);

This will pause the entire process, but won't effect the performance of the OS.
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Author Comment

by:MattC
ID: 6909457
i thought about starting a worker thread in Run() then making that a while(SERVICE_RUNNING) and then at the top of the while do a Sleep(300000) so each time round it waits 300 seconds before going round again.
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Author Comment

by:MattC
ID: 6909460
oops that should be:

while(_Module.m_status = SERVICE_RUNNING){
   Sleep(300000);

   //do code here
}
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Expert Comment

by:cookre
ID: 6909498
Sounds reasonable, as long as you don't need to be doing anything else at the time (including message processing).
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Expert Comment

by:DanRollins
ID: 6910931
>>Can ATL system services support MFC class usage?

When you create the service, the AppWizard presents that as an option.  There is a "Support MFC" checkbox.

-- Dan
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Expert Comment

by:DanRollins
ID: 6911002
oops, I see that the Support MFC checkbox gets dimmed when you select the Service radio button.  Looking at my code, for a service that uses MFC, I see that I needed to add some headers to StdAfx.h:

#include <afxwin.h>         // MFC core and standard components
#include <afxext.h>         // MFC extensions

I also see that for some reason I have this in the InitInstance:

    afxContextIsDLL= FALSE;

Alas, I did not comment the reason for that code!
-- Dan
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Expert Comment

by:jkr
ID: 6913754
Why don't you just kick off a separate thread from the service in order to do the polling work - it could be as simple as

long WINAPI TimerThread ( LPVOID pv) {

DWORD dwWait = ( DWORD) pv,

for ( ;;) {

 Sleep ( dwWait);

 // do work here...
}
}
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Expert Comment

by:jkr
ID: 6913758
BTW, if you'd like something more sophisticated than the above, check out http://support.microsoft.com/support/kb/articles/q184/7/96.asp ("HOWTO: Use a Waitable Timer with an Asynchronous Procedure Call (Q184796)") and http://msdn.microsoft.com/library/en-us/dllproc/synchro_2bcj.asp ("Using Waitable Timer Objects")
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Author Comment

by:MattC
ID: 6917760
Ah, drat as usual, excellent answer....but from completely different people.

Thanks guys.  Gimme a couple of days and I will dish out some points. :-)

MattC
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Author Comment

by:MattC
ID: 6917805
one last thing :-)

below is the Run() method.
I have put '*****************' where i think my code should go, is this right???

void CServiceModule::Run()
{
    _Module.dwThreadID = GetCurrentThreadId();

    HRESULT hr = CoInitialize(NULL);
//  If you are running on NT 4.0 or higher you can use the following call
//  instead to make the EXE free threaded.
//  This means that calls come in on a random RPC thread
//  HRESULT hr = CoInitializeEx(NULL, COINIT_MULTITHREADED);

    _ASSERTE(SUCCEEDED(hr));

    // This provides a NULL DACL which will allow access to everyone.
    CSecurityDescriptor sd;
    sd.InitializeFromThreadToken();
    hr = CoInitializeSecurity(sd, -1, NULL, NULL,
        RPC_C_AUTHN_LEVEL_PKT, RPC_C_IMP_LEVEL_IMPERSONATE, NULL, EOAC_NONE, NULL);
    _ASSERTE(SUCCEEDED(hr));

    hr = _Module.RegisterClassObjects(CLSCTX_LOCAL_SERVER | CLSCTX_REMOTE_SERVER, REGCLS_MULTIPLEUSE);
    _ASSERTE(SUCCEEDED(hr));

    LogEvent(_T("Service started"));
    if (m_bService)
        SetServiceStatus(SERVICE_RUNNING);

    MSG msg;
    while (GetMessage(&msg, 0, 0, 0))
        DispatchMessage(&msg);

************************************** //<-- My Code here

    _Module.RevokeClassObjects();

    CoUninitialize();
}
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Expert Comment

by:jkr
ID: 6917810
Well, that depends on what your code is like :o)
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Author Comment

by:MattC
ID: 6917824
:-)

see cookre's response at the top, I was gonna do something like that.
Matt
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Expert Comment

by:jkr
ID: 6917874
>>I was gonna do something like that

Uh, so your service has a UI?
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Author Comment

by:MattC
ID: 6917905
no, but the hWnd argument can be NULL.
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Expert Comment

by:jkr
ID: 6917929
Yes, but the docs to 'SetTimer()' state:

"Remarks
An application can process WM_TIMER messages by including a WM_TIMER case statement in the window procedure or by specifying a TimerProc callback function when creating the timer. When you specify a TimerProc callback function, the default window procedure calls the callback function when it processes WM_TIMER. Therefore, you need to dispatch messages in the calling thread, even when you use TimerProc instead of processing WM_TIMER."

If you don't have any UI, there will be no msg processing/dispatching...
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by:MattC
ID: 6917945
MSG msg;
while (GetMessage(&msg, 0, 0, 0))
DispatchMessage(&msg);

i thought that's what this section did?
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Expert Comment

by:jkr
ID: 6918007
Ooops :o)
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by:MattC
ID: 6918028
phew, i thought i was gonna have to rewrite a whole load of documentation there :0)
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Expert Comment

by:cookre
ID: 6918126
Documentation?
You mean there's more to this job than coding?
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Expert Comment

by:DanRollins
ID: 6919281
>>******************************* //<-- My Code here

I think you would want to start the timer above there, then handle it in the TimerProc, outside of the loop.

-- Dan

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Expert Comment

by:griessh
ID: 6957183
Dear MattC

I think you forgot this question. I will ask Community Support to close it unless you finalize it within 7 days. You can always request to keep this question open. But remember, experts can only help you if you provide feedback to their questions.
Unless there is objection or further activity,  I will suggest to split between

     "jkr, DanRollins, cookre"

comment(s) as an answer.

If you think your question was not answered at all, you can post a request in Community support (please include this link) to refund your points. The link to the Community Support area is: http://www.experts-exchange.com/commspt/

PLEASE DO NOT ACCEPT THIS COMMENT AS AN ANSWER!
======
Werner
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