Synchronizing Threads and GUI in a Delphi application

Synchronizing Threads and GUI in a Delphi application Multi-threading in Delphi lets you create applications that include several simultaneous paths of execution. A normal Delphi application is single-threaded, which means all VCL objects access their properties and execute their methods within this single thread. To speed up data processing in your application, include one or more secondary threads. Processor Threads A thread is a communication channel from an application to a processor. Single-threaded programs need communication to flow in both directions (to and from the processor) as it executes; multi-threaded apps can open several different channels, thus speeding up execution. Threads GUI When several threads are running in the application, the question arises of how you can update your graphical user interface as a result of a thread execution. The answer lies in the TThread class Synchronize method. To update your applications user interface, or main thread, from a secondary thread, you need to call the Synchronize method. This technique is a thread-safe method that avoids multi-threading conflicts that can arise from accessing object properties or methods that are not thread-safe, or using resources not in the main thread of execution. Below is an example demo that uses several buttons with progress bars, each progress bar displaying the current state of the thread execution. unit MainU;interfaceusesWindows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,Dialogs, ComCtrls, StdCtrls, ExtCtrls;type//interceptor classTButton class(StdCtrls.TButton)OwnedThread: TThread;ProgressBar: TProgressBar;end;TMyThread class(TThread)privateFCounter: Integer;FCountTo: Integer;FProgressBar: TProgressBar;FOwnerButton: TButton;procedure DoProgress;procedure SetCountTo(const Value: Integer) ;procedure SetProgressBar(const Value: TProgressBar) ;procedure SetOwnerButton(const Value: TButton) ;protectedprocedure Execute; override;publicconstructor Create(CreateSuspended: Boolean) ;property CountTo: Integer read FCountTo write SetCountTo;property ProgressBar: TProgressBar read FProgressBar write SetProgressBar;property OwnerButton: TButton read FOwnerButton write SetOwnerButton;end;TMainForm class(TForm)Button1: TButton;ProgressBar1: TProgressBar;Button2: TButton;ProgressBar2: TProgressBar;Button3: TButton;ProgressBar3: TProgressBar;Button4: TButton;Progress Bar4: TProgressBar;Button5: TButton;ProgressBar5: TProgressBar;procedure Button1Click(Sender: TObject) ;end;varMainForm: TMainForm;implementation{$R *.dfm}{ TMyThread }constructor TMyThread.Create(CreateSuspended: Boolean) ;begininherited;FCounter : 0;FCountTo : MAXINT;end;procedure TMyThread.DoProgress;varPctDone: Extended;beginPctDone : (FCounter / FCountTo) ;FProgressBar.Position : Round(FProgressBar.Step * PctDone) ;FOwnerButton.Caption : FormatFloat(0.00 %, PctDone * 100) ;end;procedure TMyThread.Execute;constInterval 1000000;beginFreeOnTerminate : True;FProgressBar.Max : FCountTo div Interval;FProgressBar.Step : FProgressBar.Max;while FCounter FCountTo dobeginif FCounter mod Interval 0 then Synchronize(DoProgress) ;Inc(FCounter) ;end;FOwnerButton.Caption : Start;FOwnerButton.OwnedThread : nil;FProgressBar.Position : FProgressBar.Max;end;procedure TMyThread.SetCountTo(const Value: Integer) ;beginFCountTo : Value;end;procedure TMyThread.SetOwnerButton(const Value: TButton) ;b eginFOwnerButton : Value;end;procedure TMyThread.SetProgressBar(const Value: TProgressBar) ;beginFProgressBar : Value;end;procedure TMainForm.Button1Click(Sender: TObject) ;varaButton: TButton;aThread: TMyThread;aProgressBar: TProgressBar;beginaButton : TButton(Sender) ;if not Assigned(aButton.OwnedThread) thenbeginaThread : TMyThread.Create(True) ;aButton.OwnedThread : aThread;aProgressBar : TProgressBar(FindComponent(StringReplace(aButton.Name, Button, ProgressBar, []))) ;aThread.ProgressBar : aProgressBar;aThread.OwnerButton : aButton;aThread.Resume;aButton.Caption : Pause;endelsebeginif aButton.OwnedThread.Suspended thenaButton.OwnedThread.ResumeelseaButton.OwnedThread.Suspend;aButton.Caption : Run;end;end;end. Thanks to Jens Borrisholt for submitting this code sample.