Boss Thread and worker threads communication

m2c

a thread shouldn't update anything in the VCL if not using synchronize or lock
instead you should let the form update itself (not in a thread)
rather give the form the information it needs in a object instance and send it a message the data changed

Hi, jaja2005,

I've made a little project for you (but I haven't finished the tests yet). See if it is something like this that you want.

To compile it, create the files which name are surrounding by '*******'.

Regards,

Douglas.

************************
 TestThread.dpr
***********************
program ThreadTest;
 
uses
  Forms,
  Mainform in 'Mainform.pas' {FMainform},
  BossWorkerThreads in 'BossWorkerThreads.pas';
 
{$R *.res}
 
begin
  Application.Initialize;
  Application.CreateForm(TFMainform, FMainform);
  Application.Run;
end.
 
 
********************************
 Mainform.dfm
********************************
 
object FMainform: TFMainform
  Left = 192
  Top = 103
  Width = 696
  Height = 480
  Caption = 'Thread Test'
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'MS Sans Serif'
  Font.Style = []
  OldCreateOrder = False
  OnClose = FormClose
  PixelsPerInch = 96
  TextHeight = 13
  object Button1: TButton
    Left = 32
    Top = 24
    Width = 113
    Height = 25
    Caption = 'Create Boss Thread'
    TabOrder = 0
    OnClick = Button1Click
  end
  object Memo1: TMemo
    Left = 24
    Top = 64
    Width = 257
    Height = 321
    TabOrder = 1
  end
  object Button2: TButton
    Left = 328
    Top = 24
    Width = 169
    Height = 25
    Caption = 'Resume Boss Thread'
    TabOrder = 2
    OnClick = Button2Click
  end
  object Button3: TButton
    Left = 168
    Top = 24
    Width = 153
    Height = 25
    Caption = 'Suspend Boss Thread'
    TabOrder = 3
    OnClick = Button3Click
  end
end
 
********************************
 Mainform.pas
********************************
unit Mainform;
 
interface
 
uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;
 
type
  TFMainform = class(TForm)
    Button1: TButton;
    Memo1: TMemo;
    Button2: TButton;
    Button3: TButton;
    procedure Button1Click(Sender: TObject);
    procedure FormClose(Sender: TObject; var Action: TCloseAction);
    procedure Button3Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
 
var
  FMainform: TFMainform;
 
implementation
 
{$R *.dfm}
 
uses BossWorkerThreads;
 
var
  b: TBossThread;
procedure TFMainform.Button1Click(Sender: TObject);
begin
  b := TBossThread.Create(3, Self);
end;
 
procedure TFMainform.FormClose(Sender: TObject; var Action: TCloseAction);
begin
  if b <> nil then
    b.Terminate;
end;
 
procedure TFMainform.Button3Click(Sender: TObject);
begin
  if b <> nil then
    b.Suspend;
end;
 
procedure TFMainform.Button2Click(Sender: TObject);
begin
  if b <> nil then
    b.Resume;
end;
 
end.
 
****************************
BossWorkerThreads.pas
****************************
unit BossWorkerThreads;
 
interface
 
uses
  SysUtils, Classes, SyncObjs, Windows, Mainform, Dialogs;
 
type
  TWorkerThread = class;
 
  TWorkerThreadResult = record
    WorkerThread: TWorkerThread;
    WorkerThreadID: Cardinal;
    Result: Boolean;
  end;
 
  PWorkerThreadResult = ^TWorkerThreadResult;
 
  TBossThread = class(TThread)
  private
    FFMainform: TFMainform;
    FSemaphore: Integer;
    FEvent: TEvent;
    FWorkerResults: TThreadList;
    FWorkerThreadList: TList;
    { Private declarations }
  protected
    procedure Execute; override;
    function SpawnThread: Boolean;
  public
    constructor Create(Semaphore: Integer; FMainform: TFMainform);
    destructor Destroy; override;
    procedure AddWorkerThreadResult(WorkerThreadResult: TWorkerThreadResult);
    property Event: TEvent read FEvent;
  end;
 
  TWorkerThread = class(TThread)
  private
    FBossThread: TBossThread;
    { Private declarations }
    function DoTest(TestFlag: Boolean): Boolean;
  protected
    procedure Execute; override;
  public
    constructor Create(BossThread: TBossThread);
  end;
 
implementation
 
{ TBossThread }
 
procedure TBossThread.AddWorkerThreadResult(WorkerThreadResult: TWorkerThreadResult);
begin
  with FWorkerResults do
  begin
    with LockList do
    try
       Add(@WorkerThreadResult);
       FEvent.SetEvent;
    finally
       UnlockList;
    end;
  end;
end;
 
constructor TBossThread.Create(Semaphore: Integer; FMainform: TFMainform);
begin
  inherited Create(True);
  FWorkerResults := TThreadList.Create;
  FWorkerThreadList := TList.Create;
  FEvent := TEvent.Create(nil, False, False, '');
  FSemaphore := Semaphore;
  FFMainform := FMainform;
  FreeOnTerminate := True;
  Resume;
end;
 
destructor TBossThread.Destroy;
var
  i: Integer;
begin
  for i := 0 to FWorkerThreadList.Count - 1 do
    TWorkerThread(FWorkerThreadList[i]).Terminate;
 
  FWorkerResults.Free;
  FEvent.Free;
  inherited;
end;
 
procedure TBossThread.Execute;
var
  List: TList;
  WorkerThreadResult: PWorkerThreadResult;
  FAvailableThreads: Boolean;
begin
  while not Terminated do
  begin
    repeat
      FAvailableThreads := SpawnThread
    until not FAvailableThreads;
 
    List := FWorkerResults.LockList;
 
    try
      if List.Count > 0 then
      begin
        WorkerThreadResult := List.Items[0];
        FFMainform.Memo1.Lines.Add('ThreadID = ' + IntToStr(WorkerThreadResult^.WorkerThreadID) + ', ' +
                                   'Result = ' + IntToStr(Integer(WorkerThreadResult^.Result)));
        FWorkerResults.Remove(WorkerThreadResult);
      end
    finally
      FWorkerResults.UnlockList;
 
      if List.Count = 0 then
      begin
        FEvent.ResetEvent;
        FEvent.WaitFor(INFINITE);
      end;
    end;
  end;
end;
 
function TBossThread.SpawnThread: Boolean;
begin
  Result := False;
 
  if FSemaphore > 0 then
  begin
    FWorkerThreadList.Add(TWorkerThread.Create(Self));
    Dec(FSemaphore);
    Result := True;
  end;
end;
 
{ TWorkerThread }
 
constructor TWorkerThread.Create(BossThread: TBossThread);
begin
  inherited Create(True);
  FBossThread := BossThread;
  FreeOnTerminate := True;
  Resume;
end;
 
function TWorkerThread.DoTest(TestFlag: Boolean): Boolean;
begin
  Result := not TestFlag;
end;
 
procedure TWorkerThread.Execute;
var
  WorkerThreadResult: TWorkerThreadResult;
  TestFlag: Boolean;
begin
  TestFlag := False;
 
  with WorkerThreadResult do
  begin
    WorkerThread := Self;
    WorkerThreadID := ThreadID;
  end;
 
  while not Terminated do
  begin
    TestFlag := DoTest(TestFlag);
    WorkerThreadResult.Result := TestFlag;
    FBossThread.AddWorkerThreadResult(WorkerThreadResult);
  end;
end;
 
end.

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Good day dougaug!
Great, many thanks.  I am going to study and test it and let you know my doubts.
See ya

Just one thing i have noticed. You use TestFlag: Boolean a single variable while i want to work with an array or list of bolean. Let me explain you my goal. At beginning the BossThread copies a sort of  
array or list of control to be performed (maybe via worker constructor) kind of:
 
A (String) - B (char or string) - C (String or Integer)  
An example:
Check if  ValueofTemperature is > of 30
 
ValueofTemperature is 'A'
'>' is B
30 is 'C'
 
So each worker thread will get its tasks to be completed from the BossThread. One workerthread may receive 10 controls to verify other less or maybe more. So the workerthread would create a sort
of array or TList of Bolean of results internally. Once the thread is done itwill inform the boss thread(maybe with postmessage) and copies the TList in a shared buffer (maybe before the thread destroy itself (OnTerminate=True)).  Now the Bossthread may picks up an item from the buffer ( where a single item is a array of TList of boolean seen before) and upadate a TListBox or whatever in my VCL main thread.

Hope it helps.
Thx

 

Ok I have understood. I will try to do something like you said and post the code here.

Regards

Great, in meanwhile i will study the previous example
Thanks a lot for your help!

dougaug, jaja2005
let me point out some things:
first of all,
you have circular unit reference :(  
this should by avoided between the mainform and the bossthread

second, you are updating the VCL from within a other thread !
this will hang up your app !!!

it's a nice start, but unforatunately will provide some problems
i'll rebuild it for you so you can use the bossthread from any form !
and show you how to do a callback to a higher object

check this article on to use a callback:
https://www.experts-exchange.com/articles/Programming/Languages/Pascal/Delphi/Displaying-progress-in-the-main-form-from-a-thread-in-Delphi.html
it works for any form
this works with a synchronised callback, but we can change this too
i will use a object to return info

let me work on this a little ...

Thank guys! Well it seems that I will have lot of thing to read before my holiday...:-)
see ya

Hi Geert, I am studyng you code and note all the question or doubts I have.
Should I expect some other code from you?

>> it's not completed....

see u.

ah..i forgot to tell u. I will be on holiday next 15 days.
If I will not renew the service now can I do it later on and access again to my open question and continue?

Thx

i'll be on holiday too for 3 weeks
i'll be working on this project for myself
i don't know when exactly it will be finished

i'll post the changes in the future, possibly in a article too

ok see you soon and enjoy your holiday.

Hi All. I am back.
I have been testing your code. I have a couple of question.

As Task I want to ping a node and get the result. I've added
a new components for this in TWorkerThread class as below:

constructor TWorkerThread.Create(CreateSuspended: Boolean; aSignalMsgEvent: TSignalWorkerEvent = nil; aUseSynchronize: boolean = True);
begin
  inherited Create(CreateSuspended);
  CreateMsgInfo;
  fSignalMsgEvent := aSignalMsgEvent;
  fUseSynchronize := aUseSynchronize;
  FPing := TipwPing.Create(nil);
 with FPing do begin
  PacketSize := 32;
  Timeout := 60; // Abandon ping attempt after 10 second
  //Idle := True;
  Tag := 0;
  OnResponse := PingThreadResponse;  FOnError := PingThreadError;
 end;


procedure TWorkerThread.PingThreadResponse(Sender: TObject; RequestId: Integer;
      const ResponseSource, ResponseStatus: string; ResponseTime: Integer);
      begin
      FThreadPingResult := ResponseStatus;
      if (ResponseStatus = 'OK') then
      SignalStatus(' Node is UP');
      SignalEnd;
      end;

procedure TWorkerThread.DoAction;
begin
FPing.PingHost('127.0.0.1');
end;

procedure TWorkerThread.Execute;
begin
  SignalBegin;
    try
     try
    DoAction;
    except
  on e: Exception do
        SignalError (e.Message);// Always fired????
     end;
     finally
     SignalEnd;
end;
end;


FPing components works like that:

if Timeout is >0 the component blocks. If the Timeout property is set to 0, all operations return immediately, potentially  failing with an error if they can't be completed immediately.

- If I specify an IP not reachable then i get correctly Timeout message with SignalError (e.Message) after 10s.
- If I specify a valid IP i.e. 127.0.0.1 I got:

- The message "Node is UP" but only after "Timeout seconds"  
- I get also the message Timeout 301 along with "Node is UP", exception is always fired.

Any suggestion?
What's wrong?
:-(


Thx

Want to be sure to undestand you code.
Please check the steps below;

1. First you inizialize the TCollection (TTaskItems) and the Critical Section objects. At very first time the Tcollection is empty.
2. You start the BossThread and in the constructor you set some fSignalMsgEvent to point to ReturningInfo in MainForm.  the fevent is created.

3. BossThread starts chekings for newtask (CheckNewTasks) to be excute in TCollection (TTaskItems). for it you use wrTimeout which value can be easly changed.

4. By Clicking on AddWorker you create an instace of TTask class and sets fStatus in tsNotStarted Status.

5. By using AddTask(x) you add a new TTaskItem to TTaskItems with this code:

with mTasks.Add do
        fTask := aTask;
       TBossThread.Warning;

mTasks.Add automactly creates an object of TTaskItem. You copy x in fTask, which is private field of TTaskItem. if I understood  correctly your approach the real job to be done is specified by ftask field right? Have seen other example where TTaskItem was create like:

TPingItem = class (TCollectionItem)
public
PingThreadId : Integer;
PingThread : TPingThread;
...

In the example above PingThead has events to be fired like PingOnReply, PinOnStatus and so on...

Your decided to use class reference in order to change the type of WorkerThread so job to be done
in DoAction right?

i stopped my further work on the thread boss and worker
i'm gonna use this for myself:
http://otl.17slon.com/

Hi. Hmm, I've studied deeply your code and i would like to have things working. The project works nice unless i use in DoAction a sample task (as you have done by using a repeat-until loop). As you can see I added a  FPing component as private filed in WorkerThread. The result I got is described above.

ID: 25367082

The example you posted it has been very useful to me to start to undestand the mechanims of exchanging signal among theads, I have to admit. I am very interested in that and learn a good approach for running task and having work done within a workerthread back to mainVCL or BossThread using delphi events. The structure would be very useful to be implemented
in different scenario where task might be everything.

Why you moved to OmniThreadLibrary? Have you been able to get the same result with Omni? Can you post the code for the example of lunching task from a BossThread?

Do you have examples project on this topic?

I was wating for an article of your on that..:-((

thx

Hi Geert.
It must be something wrong with FPing components. Indy Ping works nice.
Let you know.

I use Delphi 2006., probably it won't work. I have compiled the package and have now in palette only TOmniEventMonitor...it's all that I need...? :-(

lol, same here, threads are not visual components with events to attach
it's possible it will never be more on the palette