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Vars in TServerClientThread

Posted on 1998-10-22
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Last Modified: 2010-04-06
Hi,

I have encountered the following problem.
I am write a service for windows NT with Delphi 3 C/S. I use some NTService
unit and create a TServerSocket runtime.
I use a Threadblocking methode to spawn new threads for each new connection
to my server. This seems to work fine,
except for the fact that a global variable decleared within th
TServerClientThread wich I want to give the port of the current
connection seems to overwrite the data for this var in all the open threads.
What I mean is that if a second connection is made the variable in the first
connection gets the same value as the variable
in the second (last) connection.

This problem seems to go away when I assign a value to the variable lateron
in the program but that doesn't make verry much
sense to me, because no paticulair thing happen before it that would be able
to solve the problem.

piece of my code:

Unit ClientThread;

type
  POP3Thread = class(TServerClientThread)
...

protected
    procedure Execute; override;
...
implementation
...
var UserPort : integer;
...
procedure POP3Thread.Execute;
begin
UserPort:=ClientSocket.RemotePort;
...(loop for receiving commands follows)
end.

Thanx for anny help in advance,

Martijn Tieland

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Comment
Question by:mtieland
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8 Comments
 
LVL 27

Expert Comment

by:kretzschmar
ID: 1343862
hi mtieland,

your global-var should be in the implementation section of your unit, if so?

meikl
0
 

Author Comment

by:mtieland
ID: 1343863
I have put the vars behind the implementation section...

The strange thing is when I assign a value to these vars lateron
in the thread it some to work propperly...
0
 

Author Comment

by:mtieland
ID: 1343864
Edited text of question
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LVL 27

Expert Comment

by:kretzschmar
ID: 1343865
hi mtieland,

maybe your var should be initialized
try

var userport : Integer = 0; {or OtherNumber}

meikl
0
 
LVL 12

Expert Comment

by:rwilson032697
ID: 1343866
Perhaps the variable being overwritten should be declared with ThreadVar?
0
 

Author Comment

by:mtieland
ID: 1343867
Thanks for the hint on ThreadVar, it works great,
1 question remains dough, what is a ThreadVar kind of a thing??
0
 

Author Comment

by:mtieland
ID: 1343868
By the way I am new to this expert-exchange thing but i think rwilson should get the points, because he gave the solution to the problem.

Thanx
0
 
LVL 12

Accepted Solution

by:
rwilson032697 earned 100 total points
ID: 1343869
Thanks mtieland!

Threadvar is used to declare a variable that is in thread local storage. What this means is that every thread will see a different instance of the variable. Generally these kinds of variables are placed into a TThread derived class but sometimes you need to use threadvar...

Cheers,

Raymond.
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