Solved

TDatabase component generating error in thread

Posted on 2002-04-28
10
225 Views
Last Modified: 2010-04-04
!!!!!!!!!!!!!!!!HELP!!!!!!!!!!!!!!!!!!!!!!!!!

Now I have your attention :)

I've got a thread which runs simultaneously with my main app.  The thread processes jobs which are passed to it.  I've got a REAL problem tho, and I can't figure out what I'm doing wrong.

I've been told that each thread requires it's own TDatabase.  No worries, I'll stick on in.  Here's what I do:

constructor TReportThread.CreateThread(CreateSuspended: Boolean; Alias, Params: String);
begin
  Inherited Create(CreateSuspended);

  FreeOnTerminate := true;

  ADatabase := TDatabase.Create(nil);
  ASession := TSession.Create(nil);
  ASession.AutoSessionName := true;
  ASession.Active := true;
  ADatabase.SessionName := ASession.SessionName;
  ADatabase.AliasName := Alias;
  ADatabase.DatabaseName := 'PMREPTHREADDM';
  ADatabase.Params.Text := Params;
  ADatabase.LoginPrompt := false;
  ADatabase.Open;
end;

When the thread is created, I can trace through the code until the database is opened.

ADatabase and ASession are declared in the Private section of the class and are freed when the thread is terminated.

Any help would be appreciated.

Ta!

Stu
0
Comment
Question by:SJohnson
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 4
  • 3
  • 2
  • +1
10 Comments
 
LVL 1

Author Comment

by:SJohnson
ID: 6976328
Oops!  Forgot to add to this that the error I'm getting is C0000008
0
 
LVL 9

Expert Comment

by:ITugay
ID: 6976855
Hi SJohnson,

what is the value for CreateSuspended passed as parameter?
If your thread not suspended then execute started immediate after constructor called. In this case databse can be not initialized before some action in execute method will refer to it. Better would be to move database and session initialization code inside execute method.

------
Igor.

0
 
LVL 6

Expert Comment

by:Stuart_Johnson
ID: 6976998
Hi Igor,

I create the thread unsuspended.  And then after the constructor, change it to suspend = true.  Is this OK, or should I started it suspened?

Thanks for the info.

Stu
0
Independent Software Vendors: We Want Your Opinion

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

 
LVL 1

Expert Comment

by:adeng
ID: 6978010
I think each thread requires it's own TSession and try to make ASession.AutoSessionName := False and create your own session name for each thread.

Regards
Adeng
0
 
LVL 1

Author Comment

by:SJohnson
ID: 6978904
Hi Adeng,

From the Delphi 5 help: "Set AutoSessionName to control whether or not a unique session name is automatically generated. AutoSessionName is intended to guarantee developers of multi-threaded applications that sessions spawned for each thread are unique at runtime. "

Cheers!

Stu
0
 
LVL 9

Expert Comment

by:ITugay
ID: 6979849
Hi Stuart,

did you try to move initializtion code to execute method? The deal is that Create method executed in main VCL thread.

-----
Igor.

PS: it's not good idea to use two logins :-)
0
 
LVL 6

Expert Comment

by:Stuart_Johnson
ID: 6979905
Hi Igor,

No it didn't work :(  Everything goes OK until it reaches the Datebase.Open line and then the execute method is exitted with no exception.  If I do this:

try
  ADatabase.Open;
except
  on E: Exception do
    ShowMessage(E.Message)
end;

no error is displayed.  The application stops responding.

What do you mean by it's not a good idea to use two logins? Do you mean two different login IDs?  If so, I'm only using the one that's used to log into the actual application.

Thanks for you help,

Stu.
0
 
LVL 9

Accepted Solution

by:
ITugay earned 100 total points
ID: 6982837
Hi Stuart,

I will try to explore my HDD to find examples of DB threading. Seems it is at home. On success, I will public it here.

Two logins:
1. SJohnson
2. Stuart Johnson  
0
 
LVL 1

Author Comment

by:SJohnson
ID: 6998471
Hi Igor,

I've done this the only way I know how and the only way which works.  I use the TDatabase component from the main application.  So far I've had absolutely no problems what so ever.  I know this probably isn't right, but I've had no other choice as I had to get this part of the app working.  If you can tell me how it works, I'll be more than happy to change what I've done.

As for the two logins, it's cool for me to have the two of them.  See here: http://www.experts-exchange.com/jsp/qManageQuestion.jsp?ta=delphi&qid=20148878

Cheers,

Stu
0
 
LVL 1

Author Comment

by:SJohnson
ID: 7168623
Hi Igor,

Well, I guess we never got any further on this one.  I'm just going to giv eyou the points so that it's cleared out.

Thanks for you help with the question though!

Cheers,

Stu.
0

Featured Post

Free Tool: Port Scanner

Check which ports are open to the outside world. Helps make sure that your firewall rules are working as intended.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

A lot of questions regard threads in Delphi.   One of the more specific questions is how to show progress of the thread.   Updating a progressbar from inside a thread is a mistake. A solution to this would be to send a synchronized message to the…
The uses clause is one of those things that just tends to grow and grow. Most of the time this is in the main form, as it's from this form that all others are called. If you have a big application (including many forms), the uses clause in the in…
Michael from AdRem Software explains how to view the most utilized and worst performing nodes in your network, by accessing the Top Charts view in NetCrunch network monitor (https://www.adremsoft.com/). Top Charts is a view in which you can set seve…
Add bar graphs to Access queries using Unicode block characters. Graphs appear on every record in the color you want. Give life to numbers. Hopes this gives you ideas on visualizing your data in new ways ~ Create a calculated field in a query: …

705 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question