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Vb.NET Threads and global variables

Posted on 2007-11-28
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Last Modified: 2012-06-27
I have a globally defined variable (interface?) to my database in ApplicationEvents.vb. (public DB as TransDB)

On startup (MyApplication_Startup) it creates a new instance of the interface, and connects to the database.

then, in the rest of my program i can read/write by using
My.Application.DB.ReadFromDB(<args>)
My.Application.DB.WriteToDB(<args>)
etc.

This works through all my code, except inside a thread.

The thread is for printing and what it does is
1) show a form to allow the user to select the documents to be printed
2) extracts an embedded excel file
3) starts excel and maps data from either a) a form the user has modified, or b) from a saved entry in the database
4) prints the specified documents

inside the thread My.Application.DB is 'Nothing' and the program crashes.

why?  

How can I access this so I don't have to create a 2nd connection?

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Question by:sgaggerj
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2 Comments
 
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Accepted Solution

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jcoehoorn earned 500 total points
ID: 20366502
This is very dangerous.  Since the threads may be running simultaneously and be pre-empted at any time, by sharing the same database object between them you are creating the potential for all kinds of race condition and other concurrency issues.  Go ahead and create a 2nd connection in the thread.  Your database can handle it.
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by:sgaggerj
ID: 20395652
Ahhh.... being new to threads, that's something that didn't even cross my mind.

Thanks!
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