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Sean Veale
Guest
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 Posted: Mon Jan 26, 2004 10:07 pm Post subject: Opening a database connection in new thread. |
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I'm trying to open a database connection from a seperate thread than the
main vcl one but i have problems. Probally I can not do what I am trying to
do but I wanted to ask first.
Thank you in advance.
DB is an TADOConnection compent.
---------code---------------------------------------------------------------
------------------
void __fastcall TOpenDatabaseThread::Execute()
{
FreeOnTerminate = true;
// Check to see if we should terminate the thread.
if(Terminated) return;
// Try to connect to the database.
try
{
TestDatabases->DB->Connected = true; // This throws an exception.
}
catch(...)
{
bUnableToOpenDataBase = true;
ShowMessage("Error opening the database by a thread.");
}
//--------------------------------------------------------------------------
----
// Code that invokes the thread
TOpenDatabaseThread* OpenDataBaseThread;
// Create the thread and suspend it.
OpenDataBaseThread = new TOpenDatabaseThread(true);
if(!OpenDataBaseThread)
{
// We couldn't create the thread for some reason. Warn the user and
proceed.
MessageDlg("Unable to create database thread. There will be na delay
when saving data the first time.", mtWarning, TMsgDlgButtons() << mbOK, 0);
return;
}
OpenDataBaseThread->Priority = tpLowest;
// Start the thread
OpenDataBaseThread->Resume();
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Remy Lebeau (TeamB)
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| Posted: Mon Jan 26, 2004 11:29 pm Post subject: Re: Opening a database connection in new thread. |
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"Sean Veale" <Not a [email]Real (AT) Adress (DOT) sorr[/email]y> wrote
| Quote: | TestDatabases->DB->Connected = true; // This throws an exception.
|
What is the actual message of the exception?
Gambit
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Sean Veale
Guest
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| Posted: Tue Jan 27, 2004 9:27 pm Post subject: Re: Opening a database connection in new thread. |
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| Quote: |
TestDatabases->DB->Connected = true; // This throws an exception.
What is the actual message of the exception?
Sorry I should have posted that. The message is "CoInitialize has not |
been called." and it is of type EOleException.
Thanks
Sean
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Remy Lebeau (TeamB)
Guest
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| Posted: Tue Jan 27, 2004 9:55 pm Post subject: Re: Opening a database connection in new thread. |
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"Sean Veale" <Not a [email]Real (AT) Adress (DOT) sorr[/email]y> wrote
| Quote: | Sorry I should have posted that. The message is
"CoInitialize has not been called." and it is of type EOleException.
|
Well, then there is your answer. ADO is COM-based. Every thread that wants
to access COM needs to initialize the COM library before making any other
COM-related calls. The error is telling you exactly that - your thread did
not initialize the COM library for itself by calling CoInitialize() before
then trying to access the COM system.
Gambit
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Sean Veale
Guest
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| Posted: Wed Jan 28, 2004 2:50 pm Post subject: Re: Opening a database connection in new thread. |
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| Quote: |
Sorry I should have posted that. The message is
"CoInitialize has not been called." and it is of type EOleException.
Well, then there is your answer. ADO is COM-based. Every thread that
wants
to access COM needs to initialize the COM library before making any other
COM-related calls. The error is telling you exactly that - your thread
did
not initialize the COM library for itself by calling CoInitialize() before
then trying to access the COM system.
|
Ok, That makes sence to me. Can you give an example of how to call
CoInitialize(). Another question where in the main vcl thread is this done
for you? For example if I have this function in my data module
bool TTestDatabases::Connect()
{
try
{
DB->Connected=true;
if (DB->Connected==true) return true;
else return false;
}
catch (...)
{
ShowMessage("MJTest database alias may not be setup properly, database
use is disabled.");
return false;
}
}
I don't have a problem connecting to the database.
Thank you so far.
Sean
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Remy Lebeau (TeamB)
Guest
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| Posted: Wed Jan 28, 2004 6:58 pm Post subject: Re: Opening a database connection in new thread. |
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"Sean Veale" <Not a [email]Real (AT) Adress (DOT) sorr[/email]y> wrote
| Quote: | Ok, That makes sence to me. Can you give an example of how
to call CoInitialize().
|
void __fastcall TOpenDatabaseThread::Execute()
{
CoInitialize(NULL);
try {
//...
}
__finally {
CoUninitialize();
}
}
Or:
void __fastcall TOpenDatabaseThread::Execute()
{
CoInitialize(NULL);
//...
}
void __fastcall TOpenDatabaseThread::DoTerminate()
{
CoUninitialize();
}
Or:
#include <utilcls.h>
void __fastcall TOpenDatabaseThread::Execute()
{
TInitOle ole;
//...
}
| Quote: | Another question where in the main vcl thread is this done for you?
|
There are many places where the VCL may have already called CoInitialize()
for the main thread.
Gambit
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