We help IT Professionals succeed at work.

Check out our new AWS podcast with Certified Expert, Phil Phillips! Listen to "How to Execute a Seamless AWS Migration" on EE or on your favorite podcast platform. Listen Now

x

Boss Thread and worker threads communication

jaja2005
jaja2005 asked
on
Medium Priority
1,803 Views
Last Modified: 2013-11-23
Question: Hi. In my main application (main VCL) I want to develop a single boss
thread which:

A: is able to communicate with worker threads
B: is able to update some VCL componets properties into main VCL basing
on the worker thread results.
C: create the worker thread and limit the number of it using a semaphore

Worker threads are I/O operation. They do some test, create a sort of
array of boolean based on the test performed and store into a shared
buffer (es. TthreadList).

The approach I would like to use is the one of producer/consumer.

So the sequence should be:

- The boss spaws some worker threads
- The workers threads do some test and create a result as [TRUE,FALSE,FALSE...]
  with a size that is dynamic.

- the worker thread store it into a shared buffer, protected with Critical Section.

- The boss thread wakes up or wait to access to the buffer. When it does it
will update the propreties in the main VCL


I want to develop this structure without using Syncronize and above all

limiting the buffer size and taking care of flow control between boss an
workers.
Comment
Watch Question

Geert GOracle dba
CERTIFIED EXPERT
Top Expert 2009

Commented:
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
CERTIFIED EXPERT

Commented:
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.

Open in new window

Author

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

Author

Commented:
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

 
CERTIFIED EXPERT

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

Regards

Author

Commented:
Great, in meanwhile i will study the previous example
Thanks a lot for your help!
Geert GOracle dba
CERTIFIED EXPERT
Top Expert 2009

Commented:
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 ...
Oracle dba
CERTIFIED EXPERT
Top Expert 2009
Commented:
Unlock this solution and get a sample of our free trial.
(No credit card required)
UNLOCK SOLUTION
Geert GOracle dba
CERTIFIED EXPERT
Top Expert 2009
Commented:
Unlock this solution and get a sample of our free trial.
(No credit card required)
UNLOCK SOLUTION

Author

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

Author

Commented:
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.

Author

Commented:
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

Geert GOracle dba
CERTIFIED EXPERT
Top Expert 2009

Commented:
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

Author

Commented:
ok see you soon and enjoy your holiday.

Author

Commented:
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

























Author

Commented:
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?
Geert GOracle dba
CERTIFIED EXPERT
Top Expert 2009

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

Author

Commented:
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





Author

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

Geert GOracle dba
CERTIFIED EXPERT
Top Expert 2009
Commented:
Unlock this solution and get a sample of our free trial.
(No credit card required)
UNLOCK SOLUTION

Author

Commented:
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...? :-(
Geert GOracle dba
CERTIFIED EXPERT
Top Expert 2009

Commented:
lol, same here, threads are not visual components with events to attach
it's possible it will never be more on the palette
Unlock the solution to this question.
Thanks for using Experts Exchange.

Please provide your email to receive a sample view!

*This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.

OR

Please enter a first name

Please enter a last name

8+ characters (letters, numbers, and a symbol)

By clicking, you agree to the Terms of Use and Privacy Policy.