Call the TDataModule method in TThread.Execute

Question

In general, is it possible in the TThread.Execute procedure to call the TDataModule method, in which there is no visual activity?

Thanks to everyone, Massimo.

Answer 1

The easiest way is to use TThread.Synchronize to call a method in your data module.

However, if you do not want to do this, even if the visual activity is not involved, you must determine whether you need to add a critical section to protect you.

VCL, (TButton) ( ), UNSAFE. (, ) .

:

    if Assigned(MyDataModule) then MyDataModule.DoSomething(a,b,c);

, , , , FList :

/// DoSomething: Note this method must be thread-safe!
procedure TMyDataModule.DoSomething(a:TMyObject1;b:TMyObject2;c:TMyObject3);
begin
   FCriticalSection.Enter;
   try
     if not FList.Contains(a) then
       FList.Add(a); 
     ...
   finally
   FCriticalSection.Leave;
   end;
end;

/// elsewhere in the same data module, wherever anybody modifies or checks the state 
/// (content) of FList, wrap the method with a critical section like this:
function TMyDataModule.HasItem(a:TMyObject1):Boolean;
begin
   FCriticalSection.Enter;
   try
     result := FList.Contains(a); 
   finally
     FCriticalSection.Leave;
   end;
end;

Delphi :

• , .
• , , .., concurrency, , , ( ) . , . , .
• - VCL, PostMessage, TThread.Synchronize - , - .
  • , , . , , , , , , .

Answer 2

:

: Windows , GUI . (, , , .., ). , , TDataModule - "GUI-" (, ShowMessage), .

UPDATE: , , - ( , Synchronize ..). , "" , .

Answer 3

, : .

, (.. ), .

TMyDataModule = class(TDataModule)
public
  function AddOne(const Value: Integer): Integer;
end;

function TMyDataModule.AddOne(const Value: Integer): Integer;
begin
  Result := Value + 1;
end;

---

, , , .

TMyDataModule = class(TDataModule)
private
  FNumber: Integer
public
  function AddOne(const Value: Integer): Integer;
end;

function TMyDataModule.AddOne(const Value: Integer): Integer;
begin
  FNumber := Value
  //***** A context switch here will mess up the result of (at least) one thread.
  Result := FNumber + 1;
end;

. TQuery, TTable, GUI, ,... .

Answer 4

, .

, , , .
.

Answer 5

, .

- , , TChart, , . ( TIdTcpServer ) .

() () . ( 3): ( Datamodule).

, :

1) , GUI;

2) , .

Datamodule ( TIdTcpClient ), ( , , , ).

unit dtmPDoxClientU;

  TdtmPDoxClient = class(TDataModule)
    IdTCPClient: TIdTCPClient;
    ...
    function GetData(...): boolean; 
    ...
  end;

---

unit frmChartBaseFormU;

  TfrmChartBaseForm = class(TForm)
    ...
    TheThread: TThreadClient;
    procedure WMThreadComm(var Message: TMessage); message WM_THREADCOMM;
    procedure ListenThreadEvents(var Message: TMessage); virtual;
    procedure ExecuteInThread(AThread: TThreadClient); virtual;
  end;

  TThreadClient = class(TThread)
  private
  public
    Task: integer;
    Module: TfrmChartBaseForm;
    procedure Execute; override;
    property Terminated;
  end;

procedure TfrmChartBaseForm.FormCreate(Sender: TObject);
  ...
  TheThread := TThreadClient.Create(true);
  with TheThread do begin
    Module := self;
    FreeOnTerminate := true;
  end;//with
end;//FormCreate

procedure TfrmChartBaseForm.WMThreadComm(var Message: TMessage);
begin
  ListenThreadEvents(Message);
end;//WMThreadComm

procedure TfrmChartBaseForm.ListenThreadEvents(var Message: TMessage);
begin
// do override in derived classes
end;//ListenThreadEvents

procedure TfrmChartBaseForm.ExecuteInThread(AThread: TThreadClient);
begin
// do override in derived classes
end;//ExecuteInThread

procedure TThreadClient.Execute;
begin
  with Module do begin
    ExecuteInThread(self);
  end;//with
end;//Execute

, VFI, :

unit dtmPDoxClientDataOIU;

  TdtmPDoxClientDataOI = class(TdtmPDoxClient)
    cdsClient_IS: TClientDataSet;
    ...
    dsr_I: TDataSource;
    ...
  private
  public
  end;

---

unit frmPDoxClientDataOIU;

  TfrmPDoxClientDataOI = class(TfrmChartBaseForm)
    ChartOI: TChart;
    ...
    procedure FormCreate(Sender: TObject);
  public
    { Public declarations }
    dtmPDoxClientDataOI: TdtmPDoxClientDataOI;
    procedure ListenThreadEvents(var Message: TMessage); override;
    procedure ExecuteInThread(AThread: TThreadClient); override;
  end;

procedure TfrmPDoxClientDataOI.FormCreate(Sender: TObject);
begin
  inherited;
  dtmPDoxClientDataOI := TdtmPDoxClientDataOI.Create(self);
  TheThread.Task := 1;
  TheThread.Resume;
end;//FormCreate

procedure TfrmPDoxClientDataOI.ListenThreadEvents(var Message: TMessage);
begin
  if (Message.WParam = 1) then begin
    case Message.LParam of
      //GUI tasks, using ClientDataset already compiled and not re-used
    end;//case
  end;//if
end;//ListenThreadEvents

procedure TfrmPDoxClientDataOI.ExecuteInThread(AThread: TThreadClient);
begin
  while not AThread.Terminated and (AThread.Task <> 0) do begin
    case AThread.Task of
      1: begin
        if dtmPDoxClientDataOI.GetData(...) then
          if not AThread.Terminated then begin
            PostMessage(Handle,WM_THREADCOMM,1,1);
            AThread.Task := 2;
          end //if
          else
            AThread.Task := 0;
      end;//1
      ... etc...
    end;//case
  end;//while
end;//ExecuteInThread

So, when the end user clicks the button, a new form appears and its own datamodule and a stream is created; the thread uses its own datamodule using the ExecuteInThread function. When the data is ready, PostMessage is sent to a form that updates the chart.