Threading in Delphi.
Yesterday I had to realize a simple task: Load data from the database into a ComboBox in a separate thread. Threading in Delphi turned out to be quite easy. But still I faced several difficulties, i.e. weird effects. My thread looks pretty simple:
type
TDataLoaderThread = class(TThread)
myDBConnection: TADOConnection;
query1: TADOQuery;
query2: TADOQuery;
private
protected
procedure InitData;
procedure Execute; override;
implementation
procedure TDataLoaderThread.Execute;
begin
inherited;
FreeOnTerminate:=True;
Priority := tpLower;
Synchronize(InitData);
end;
procedure TDataLoaderThread.InitData();
begin
// code for retrieving data from the DB
// and filling the ComboBox of the Form object
end;
I start this thread within my GUI, i.e. Form1. Method InitData is called by means of Synchronize()-method, which allows DataLoaderThread to continue execution in the context of the main thread. InitData sets the items of the ComboBox. Important issues:
1. There should be one DB connection per thread!
2. Calling Form1 by ShowModal blocks DataLoaderThread.
3. Inserting Sleep into DataLoaderThread blocks the main thread, i.e. Form1 for X ms.