BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  TThread and Database connection          BorlandTalk.com Forum Index -> C++ Builder (VCL Components Usage) View previous topic :: View next topic   Author Message Daryl Guest Posted: Sun May 06, 2007 6:50 am    Post subject: TThread and Database connection Hi all I am looking for ideas to write a NT Service that uses a TThread to watch a folder. The thread will watch a folder and process a file when found, part of this processing will involve looking up a database to get some information based on a value found in the file. My question what is the best way to handle this database connection? Would I make the connection in the Main Thread or in the (in this case) the only worker thread.? If I did create the connection in the Main Thread then how could I pass this connection to the worker thread? How would connection exceptions be managed? I was considering writing exceptions to a file. Any help would be good. thanks daryl Back to top JD Guest Posted: Sun May 06, 2007 8:10 am    Post subject: Re: TThread and Database connection "Daryl" <devaccount (AT) hotmail (DOT) com> wrote: Quote: [...] Would I make the connection in the Main Thread Yes. Quote: how could I pass this connection to the worker thread? Don't. Have the worker thread do the monitoring only and when it detects a change, have it send a message to the main thread. Quote: How would connection exceptions be managed? As usual ... in the main thread. ~ JD Back to top Daryl Guest Posted: Sun May 06, 2007 1:33 pm    Post subject: Re: TThread and Database connection JD Thanks fro the response, could you please help some more? I have placed some questions in the text below. Quote: [...] Would I make the connection in the Main Thread Yes. To establish the connection to the database when the service first starts may be an issue as the server, if local, may not be running? Any comments on this? Quote: how could I pass this connection to the worker thread? Don't. Have the worker thread do the monitoring only and when it detects a change, have it send a message to the main thread. How would you send this message, an example would be good? I am guessing that the filename would be passed, is that right? Quote: How would connection exceptions be managed? As usual ... in the main thread. Back to top JD Guest Posted: Sun May 06, 2007 6:41 pm    Post subject: Re: TThread and Database connection "Daryl" <devaccount (AT) hotmail (DOT) com> wrote: Quote: To establish the connection to the database when the service first starts may be an issue as the server, if local, may not be running? Caution: A Service should not have any GUI in it. While it's possible, it's not reccommended and it's no longer possible with Vista. Other than that, as for Services, I know very little. Quote: How would you send this message, an example would be good? I am guessing that the filename would be passed, is that right? The thread could pass the file name but I would advise against that because that's not how the Change Notification works. You are only notified that a change has happened to the folder. It's up to you to determine what the change was. For example (untested): //------------------------------------------------------------- #ifndef MainH #define MainH //------------------------------------------------------------- #include <Classes.hpp> #include <Controls.hpp> #include <StdCtrls.hpp> #include <Forms.hpp> //------------------------------------------------------------- #include "MonitorThread.h" //------------------------------------------------------------- class TForm1 : public TForm { __published: protected: virtual void __fastcall WndProc(TMessage &Message); private: TMonitorThread *FMonitorThread; public: __fastcall TForm1(TComponent* Owner); __fastcall ~TForm1(); }; //------------------------------------------------------------- extern PACKAGE TForm1 *Form1; //------------------------------------------------------------- #endif //------------------------------------------------------------- #include <vcl.h> #pragma hdrstop #include "Main.h" //------------------------------------------------------------- #pragma package(smart_init) #pragma resource "*.dfm" TForm1 *Form1; //------------------------------------------------------------- __fastcall TForm1::TForm1(TComponent* Owner) : TForm( Owner ) { FMonitorThread = new TMonitorThread( true, Handle ); FMonitorThread->SetWatchPath( "C:/SomePath" ); FMonitorThread->Resume(); } //------------------------------------------------------------- __fastcall TForm1::~TForm1() { FMonitorThread->Terminate(); FMonitorThread->WaitFor(); delete FMonitorThread; } //------------------------------------------------------------- void __fastcall TForm1::WndProc( TMessage &Message ) { if( Message.Msg == APP_FILECHANGE_NOTIFICATION ) { ShowMessage( "Changed" ); } else TForm::WndProc(Message); } //------------------------------------------------------------- //------------------------------------------------------------- #ifndef MonitorThreadH #define MonitorThreadH //------------------------------------------------------------- #include <Classes.hpp> //------------------------------------------------------------- #define APP_FILECHANGE_NOTIFICATION (WM_USER + 100) //------------------------------------------------------------- class TMonitorThread : public TThread { private: HWND FhWnd; HANDLE FChangeHandle; AnsiString FWatchPath; DWORD dwStatus; protected: void __fastcall Execute(); public: void __fastcall MonitorTerminate(TObject *Sender); __fastcall TMonitorThread( bool, HWND, AnsiString ); }; //------------------------------------------------------------- #endif //------------------------------------------------------------- //#include <vcl.h> #pragma hdrstop #include "MonitorThread.h" //------------------------------------------------------------- __fastcall TMonitorThread::TMonitorThread(bool CreateSuspended, HWND hWnd, AnsiString APath ) : TThread(CreateSuspended) { FChangeHandle = INVALID_HANDLE_VALUE; FhWnd = hWnd; FWatchPath = APath; OnTerminate = MonitorTerminate; } //------------------------------------------------------------- void __fastcall TMonitorThread::MonitorTerminate(TObject *Sender) { if( FChangeHandle != INVALID_HANDLE_VALUE ) { FindCloseChangeNotification( FChangeHandle ); } } //------------------------------------------------------------- void __fastcall TMonitorThread::Execute() { FChangeHandle = FindFirstChangeNotification( FWatchPath.c_str(), FALSE, FILE_NOTIFY_CHANGE_LAST_WRITE ); if( FChangeHandle != INVALID_HANDLE_VALUE ) { while( !Terminated ) { switch( WaitForSingleObject(FChangeHandle, 500) ) { case WAIT_OBJECT_0: PostMessage( FhWnd, APP_FILECHANGE_NOTIFICATION, NULL, NULL ); if( ! FindNextChangeNotification(FChangeHandle) ) Terminate(); break; case WAIT_TIMEOUT: break; default : Terminate(); break; } } FindCloseChangeNotification(FChangeHandle); } } //------------------------------------------------------------- Notice that I used PostMessage instead of SendMessage because SendMessage will block the thread until you have completely processed the message and SendMessage returns. ~ JD Back to top JD Guest Posted: Sun May 06, 2007 6:44 pm    Post subject: Re: TThread and Database connection "JD" <nospam (AT) nospam (DOT) com> wrote: Quote: FMonitorThread = new TMonitorThread( true, Handle ); FMonitorThread->SetWatchPath( "C:/SomePath" ); FMonitorThread = new TMonitorThread( true, Handle, "C:/SomePath" ); ~ JD Back to top Remy Lebeau (TeamB) Guest Posted: Mon May 07, 2007 10:40 pm    Post subject: Re: TThread and Database connection "Daryl" <devaccount (AT) hotmail (DOT) com> wrote in message news:463d3483 (AT) newsgroups (DOT) borland.com... Quote: I am looking for ideas to write a NT Service that uses a TThread to watch a folder. The thread will watch a folder and process a file when found The OS has notifications available for that. Look at FindFirst/NextChangeNotification() and SHChangeNotifyRegister(). Quote: what is the best way to handle this database connection? Unless your underlying database engine is thread-safe, then I suggest you create a separate connection in each thread that needs to access the database. Quote: Would I make the connection in the Main Thread I would not suggest that, no. Especially since TService runs in its own worker thread anyway, so there is not much happening in the main thread. Gambit Back to top Remy Lebeau (TeamB) Guest Posted: Mon May 07, 2007 10:42 pm    Post subject: Re: TThread and Database connection "JD" <nospam (AT) nospam (DOT) com> wrote in message news:463d557f$1 (AT) newsgroups (DOT) borland.com... Quote: [...] Would I make the connection in the Main Thread Yes. Not in a service, you wouldn't. Quote: Have the worker thread do the monitoring only and when it detects a change, have it send a message to the main thread. There is nothing in the main thread to receive and process custom messages. TService runs in a worker thread, not the main thread Quote: How would connection exceptions be managed? As usual ... in the main thread. Not for a service, no. Gambit Back to top JD Guest Posted: Mon May 07, 2007 11:17 pm    Post subject: Re: TThread and Database connection "Remy Lebeau \(TeamB\)" <no.spam (AT) no (DOT) spam.com> wrote: Quote: Not in a service, you wouldn't. I missed that he was writing a Service until I read his reply. ~ JD Back to top Daryl Guest Posted: Wed May 09, 2007 3:05 am    Post subject: Re: TThread and Database connection "Remy Lebeau (TeamB)" <no.spam (AT) no (DOT) spam.com> wrote in message news:463f6498$1 (AT) newsgroups (DOT) borland.com... Quote: "Daryl" <devaccount (AT) hotmail (DOT) com> wrote in message news:463d3483 (AT) newsgroups (DOT) borland.com... I am looking for ideas to write a NT Service that uses a TThread to watch a folder. The thread will watch a folder and process a file when found The OS has notifications available for that. Look at FindFirst/NextChangeNotification() and SHChangeNotifyRegister(). OK, I understand I have this part working I think reasonably well. This occurs in the single worker thread. One question - How would you suggest that I set-up the folder to watch, folder to move files to, folder that contains the log file, the server and database name? Would it be best to have an INI file that is read by the TService thread at start up and then it passes this information to the single worker thread so it can set up its connections. I suppose this leads to another question - if the database connection information does not result in a successful connection how would this be managed? I can see that it cold write this to a log file but is it possible to shut down the thread? Quote: what is the best way to handle this database connection? Unless your underlying database engine is thread-safe, then I suggest you create a separate connection in each thread that needs to access the database. I plan to only have one thread that will watch the folder and write to the file or NT log so I will create the DB connection in it. One question - Quote: Would I make the connection in the Main Thread I would not suggest that, no. Especially since TService runs in its own worker thread anyway, so there is not much happening in the main thread. I was thinking that TService was the main thread and the TThread I create as the worker, so there is no Main thread? Back to top Daryl Guest Posted: Sun May 13, 2007 8:10 am    Post subject: Re: TThread and Database connection Did not quite know how to place this back into the system... hope this does not contravene any rules. "Remy Lebeau (TeamB)" <no.spam (AT) no (DOT) spam.com> wrote in message news:463f6498$1 (AT) newsgroups (DOT) borland.com... Quote: "Daryl" <devaccount (AT) hotmail (DOT) com> wrote in message news:463d3483 (AT) newsgroups (DOT) borland.com... I am looking for ideas to write a NT Service that uses a TThread to watch a folder. The thread will watch a folder and process a file when found The OS has notifications available for that. Look at FindFirst/NextChangeNotification() and SHChangeNotifyRegister(). OK, I understand I have this part working I think reasonably well. This occurs in the single worker thread. One question - How would you suggest that I set-up the folder to watch, folder to move files to, folder that contains the log file, the server and database name? Would it be best to have an INI file that is read by the TService thread at start up and then it passes this information to the single worker thread so it can set up its connections. I suppose this leads to another question - if the database connection information does not result in a successful connection how would this be managed? I can see that it cold write this to a log file but is it possible to shut down the thread? Quote: what is the best way to handle this database connection? Unless your underlying database engine is thread-safe, then I suggest you create a separate connection in each thread that needs to access the database. I plan to only have one thread that will watch the folder and write to the file or NT log so I will create the DB connection in it. One question - Quote: Would I make the connection in the Main Thread I would not suggest that, no. Especially since TService runs in its own worker thread anyway, so there is not much happening in the main thread. I was thinking that TService was the main thread and the TThread I create as the worker, so there is no Main thread? Back to top Daryl Guest Posted: Sun May 13, 2007 8:10 am    Post subject: Re: TThread and Database connection Did not quite know how to place this back into the system... hope this does not contravene any rules. "Remy Lebeau (TeamB)" <no.spam (AT) no (DOT) spam.com> wrote in message news:463f6498$1 (AT) newsgroups (DOT) borland.com... Quote: "Daryl" <devaccount (AT) hotmail (DOT) com> wrote in message news:463d3483 (AT) newsgroups (DOT) borland.com... I am looking for ideas to write a NT Service that uses a TThread to watch a folder. The thread will watch a folder and process a file when found The OS has notifications available for that. Look at FindFirst/NextChangeNotification() and SHChangeNotifyRegister(). OK, I understand I have this part working I think reasonably well. This occurs in the single worker thread. One question - How would you suggest that I set-up the folder to watch, folder to move files to, folder that contains the log file, the server and database name? Would it be best to have an INI file that is read by the TService thread at start up and then it passes this information to the single worker thread so it can set up its connections. I suppose this leads to another question - if the database connection information does not result in a successful connection how would this be managed? I can see that it cold write this to a log file but is it possible to shut down the thread? Quote: what is the best way to handle this database connection? Unless your underlying database engine is thread-safe, then I suggest you create a separate connection in each thread that needs to access the database. I plan to only have one thread that will watch the folder and write to the file or NT log so I will create the DB connection in it. One question - Quote: Would I make the connection in the Main Thread I would not suggest that, no. Especially since TService runs in its own worker thread anyway, so there is not much happening in the main thread. I was thinking that TService was the main thread and the TThread I create as the worker, so there is no Main thread? 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