Delphi Thread

Dengan thread, aplikasi dapat mengerjakan satu atau lebih perintah secara bersama, dalam artian perintah satu tidak menunggu selesainya perintah sebelumnya bila akan dikerjakan. Variabel-variabel dalam tiap perintah dapat independen dan tidak saling mengganggu untuk tiap-tiap perintah yang ada. Sistem operasi yang mendukung multitasking mengijinkan perintah-perintah dikerjakan secara bersamaan dengan thread.

Thread dipakai bila:

• diperlukan proses-proses yang independent, misalnya : hardware pooling, animasi obyek
• aplikasi dengan multiprosessor
• diperlukan proses ‘idle’ dalam waktu kerjanya
• ingin belajar thread tentunya..

Contoh sederhana ini menggunakan tiga thread yang masing-masing melakukan counter mandiri dari 0 ke 100000

Inisialisasi thread :
type
TThreadSatu = class(TThread)
private
VarLokal: Integer;
protected
public
constructor CreateIt;
procedure Execute; override;
destructor Destroy; override;
end;

TThreadDua = class(TThread)
private
VarLokal: Integer;
protected
public
constructor CreateIt;
procedure Execute; override;
destructor Destroy; override;
end;

TThreadTiga = class(TThread)
private
VarLokal: Integer;
protected
public
constructor CreateIt;
procedure Execute; override;
destructor Destroy; override;
end;

TForm1 = class(TForm)
Button1: TButton;
Label1: TLabel;
Label2: TLabel;
Label3: TLabel;
Label4: TLabel;
Label5: TLabel;
Label6: TLabel;
procedure FormCreate(Sender: TObject);
procedure FormClose(Sender: TObject; var Action: TCloseAction);
procedure Button1Click(Sender: TObject);
procedure pesan1(Sender:TObject);
procedure pesan2(Sender:TObject);
procedure pesan3(Sender:TObject);
private
CriticalSection: TCriticalSection;
tred1:TThreadSatu;
tred2:TThreadDua;
tred3:TThreadTiga;
public

end;

Jangan lupa menjabarkan constructor, destructor dan executenya :
constructor TThreadSatu.CreateIt;
begin
inherited Create(true); // thread di suspend dulu
FreeOnTerminate:=true;
Form1.Label3.Caption:='';
Suspended:=false; // suspend dilepas, thread dieksekusi
end;

constructor TThreadDua.CreateIt;
begin
inherited Create(true); // thread di suspend dulu
FreeOnTerminate:=true;
Form1.Label4.Caption:='';
Suspended:=false; // suspend dilepas, thread dieksekusi
end;

constructor TThreadTiga.CreateIt;
begin
inherited Create(true); // thread di suspend dulu
FreeOnTerminate:=true;
Form1.Label6.Caption:='';
Suspended:=false; // suspend dilepas, thread dieksekusi
end;

procedure TThreadSatu.Execute;
begin
repeat
Form1.CriticalSection.Acquire;
try
Application.ProcessMessages;
Inc(VarLokal);
Form1.Label1.Caption:=inttostr(VarLokal);
finally
Form1.CriticalSection.Release;
end;
until VarLokal=100000;
end;

procedure TThreadDua.Execute;
begin
repeat
Form1.CriticalSection.Acquire;
try
Application.ProcessMessages;
Inc(VarLokal);
Form1.Label2.Caption:=inttostr(VarLokal);
finally
Form1.CriticalSection.Release;
end;
until VarLokal=100000;
end;

procedure TThreadTiga.Execute;
begin
repeat
Form1.CriticalSection.Acquire;
try
Application.ProcessMessages;
Inc(VarLokal);
Form1.Label5.Caption:=inttostr(VarLokal);
finally
Form1.CriticalSection.Release;
end;
until VarLokal=100000;
end;

destructor TThreadSatu.Destroy;
begin
inherited Destroy;
end;

destructor TThreadDua.Destroy;
begin
inherited Destroy;
end;

destructor TThreadTiga.Destroy;
begin
inherited Destroy;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
CriticalSection:=TCriticalSection.Create; // Critical Section dibuat
end;

procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);
begin
CriticalSection.Free; // Critical Section dilepas
end;

procedure TForm1.pesan1(Sender:TObject);
begin
Label3.Caption:='Thread satu selesai';
end;

procedure TForm1.pesan2(Sender:TObject);
begin
Label4.Caption:='Thread dua selesai';
end;

procedure TForm1.pesan3(Sender:TObject);
begin
Label6.Caption:='Thread tiga selesai';
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
tred1:=TThreadSatu.CreateIt;
tred1.OnTerminate:=pesan1; // tred1 utk akhir operasinya berada di proses pesan1
tred2:=TThreadDua.CreateIt;
tred2.OnTerminate:=pesan2; // tred2 utk akhir operasinya berada di proses pesan2
tred3:=TThreadTiga.CreateIt;
tred3.OnTerminate:=pesan3; // tred3 utk akhir operasinya berada di proses pesan3
end;

CriticalSection dipakai bila thread mengakses variabel global, kelas TCriticalSection memerlukan “SyncObjs” di deklarasi global uses