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Log file

Posted on 2001-06-11
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Last Modified: 2010-05-18
I have application base on paradox with multi threads.
I wish to make log file (Ascii).

what is the best way to open / write an ascii file ?

I prefer that the methods will threads safe ...

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Asi

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Question by:asi
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edsteele earned 200 total points
ID: 6177446
Unless you are using an object with built in locking, you will probably need to use a TCriticalSection object.


...

var
  MyLogLock: TCriticalSection

...

  MyLogLock := TCriticalSection.Create;

...

MyLogLock.Acquire; { lock out other threads }

try
  { Do your log functions here! }
finally
  MyLogLock.Release;
end;

My suggestion for opening and writing to the ASCII file would be to use a TStringStream.  Allow the threads to write to an intermediate location (a TStringList, maybe) and have the main application thread be in charge of periodic log updates.  CAUTION: Remember to acquire a lock from MyLogLock before doing this so the threads don't try to update the TStringList while the main thread is reading from it.

The code for using TStringStream in this case is very easy:

procedure UpdateLogFile;
var
  MyStream: TStringStream;
  i: Integer;
begin
  MyStream := TStringStream.Create('C:\Logs\MyApp.log');
  try
    MyStream.Seek(0, soFromEnd);

    MyLogLock.Acquire; { lock out other threads }

    try
      for i := 0 to LogList.Count - 1 do
        MyStream.WriteString(LogList[i]);
      LogList.Clear;
    finally
      MyLogLock.Release;
    end;
  finally
    MyStream.Free;
  end;
end;

Good Luck!
Eric
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