[SOLVED] Passing a variable exclusive to a thread
lazarus / 21-General

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torbente · 2021-03-30 23:40

Using lazarus 2.0.10 on win 8.1

This is pseudo code:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i TThreadOne
= class(TThread)    procedure Execute; override; 
end; MySpecialVariable : int64; MyThreads: array [1..10] of
TThreadOne;  For counter 1 to 10 do   begin   If
Assigned(MyThreads[counter]) then MyThreads[counter].terminate; 
 delay(10);   MyThreads[counter] := TThreadOne.Create(true); 
 MyThreads[counter].FreeOnTerminate:=true;   MyThreads[counter].Start;
   end procedure TThreadOne.Execute;    BeginMySpecialvariable {do
many things with this variable}End
My question: How i could pass a different MySpecialvariable value to
each thread?
Thanks.

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engkin · 2021-03-30 23:52

Depends on what you are tring to do, use Threadvar, or have similar
array for that variable, one for each thread and give the thread its
index in that array.

As a side note, this line is not safe if you have your threads started
with FreeOnTerminate is True:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i    If
Assigned(MyThreads[counter]) then MyThreads[counter].terminate;
and the thead will not end instantly after this call.

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torbente · 2021-03-31 01:08

Quote from: engkin on March 31, 2021, 01:52:38 amDepends on what you
are tring to do, use Threadvar, or have similar array for that
variable, one for each thread and give the thread its index in that
array.

As a side note, this line is not safe if you have your threads started
with FreeOnTerminate is True:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i    If
Assigned(MyThreads[counter]) then MyThreads[counter].terminate;
and the thead will not end instantly after this call.

AFAIK, threadvar always assign the same value to all threads and then
it becomes a thread-local var. I want that each thread have a
different value from its beggining. Or how i could detect, inside the
thread, what index of the thread array it is?

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i If
Assigned(MyThreads[counter]) then    try 
 MyThreads[counter].terminate;   finally   end;
It is safe now?

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engkin · 2021-03-31 02:58

No, not safe.

As for the variable, add it (the index)  to the thread class
TThreadOne

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PascalDragon · 2021-03-31 06:53

Quote from: torbente on March 31, 2021, 03:08:43 amIt is safe now?

No. General rule is: if FreeOnTerminate is set to True do not access
the thread instance from outside anymore. The only exception is if you
for sure know that the thread is running a loop and it will only
terminate if you trigger some action (e.g. calling TThread.Terminate).

Quote from: torbente on March 31, 2021, 03:08:43 amAFAIK, threadvar
always assign the same value to all threads and then it becomes a
thread-local var. I want that each thread have a different value from
its beggining. Or how i could detect, inside the thread, what index of
the thread array it is?

If you want each thread to have a different value, why don't you
simply pass it in as part of the constructor?

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i type 
TThreadOne = class(TThread)  private    fMySpecialVariable: Int64; 
protected    procedure Execute; override;  public    constructor
Create(aMySpecialVariable: Int64);  end; constructor
TThreadOne.Create(aMySpecialVariable: Int64);begin  inherited
Create(True);  fMySpecialVariable := aMySpecialVariable;end;

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torbente · 2021-03-31 12:26

QuoteQuote from: torbente on Today at 03:08:43 am
It is safe now?

No. General rule is: if FreeOnTerminate is set to True do not access
the thread instance from outside anymore. The only exception is if you
for sure know that the thread is running a loop and it will only
terminate if you trigger some action (e.g. calling TThread.Terminate).
Ok i removed it. Since threads are a loop (repeat... until
finishthread= true) i just added this to verify that all threads are
terminated before creating it again:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
finishthread := true;Delay(100);finishthread := false;
For the variable, i will try using counter as a global variable so
each thread can get its value.
Something like this:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i TThreadOne
= class(TThread)    procedure Execute; override;  end; {Global
variables} MySpecialVariable : int64;TCounter : integer;StropThread :
boolean; MyThreads: array [1..10] of TThreadOne; Procedure
LaunchThreads();begin StropThread := true;delay(100)StropThread :=
false;For TCounter := 1 to 10 do   begin   MyThreads[TCounter] :=
TThreadOne.Create(true);   MyThreads[TCounter].FreeOnTerminate:=true; 
 MyThreads[TCounter].Start;   Delay(10);   endend; procedure
TThreadOne.Execute;   var  MySpecialvariable : integer;
BeginMySpecialvariable := TCounter;Repeat{use of
MySpecialvariable}until StropThread;End 
This should work, but threads are so complex that i will try it first.

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ASerge · 2021-03-31 14:23

Quote from: torbente on March 31, 2021, 02:26:52 pmCode: Pascal
 [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
//...Procedure LaunchThreads();begin StropThread :=
true;delay(100)StropThread := false;For TCounter := 1 to 10 do 
 begin   MyThreads[TCounter] := TThreadOne.Create(true); 
 MyThreads[TCounter].FreeOnTerminate:=true; 
 MyThreads[TCounter].Start;   Delay(10);   endend; procedure
TThreadOne.Execute;   var  MySpecialvariable : integer;
BeginMySpecialvariable := TCounter;Repeat{use of
MySpecialvariable}until StropThread;End 
This should work, but threads are so complex that i will try it first.
In this case, all threads can get the same value of MySpecialVariable.
In addition, since the threads itself are released, why do you need an
array of references to it's?
Example:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i {$APPTYPE
CONSOLE}{$MODE OBJFPC} uses Classes; type  TThreadOne =
class(TThread)  protected    procedure Execute; override;  public   
constructor Create;  end; var  GActiveThreadsCount: Integer = 0; 
GStopWhenNotZero: Integer = 0; constructor TThreadOne.Create;begin 
inherited Create(False);  FreeOnTerminate := True;end; procedure
TThreadOne.Execute;var  MySpecialVariable: Integer;begin 
MySpecialVariable := InterlockedIncrement(GActiveThreadsCount);  try 
 while GStopWhenNotZero = 0 do    begin      {use of
MySpecialVariable}      Writeln('Thread ID=', ThreadID, ',
MySpecialvariable=', MySpecialVariable);      MySpecialVariable :=
MySpecialVariable * 10;      Sleep(250);    end;  finally   
InterlockedDecrement(GActiveThreadsCount);  end;end; procedure
TerminateThreads;begin  Writeln('TerminateThreads'); 
InterlockedIncrement(GStopWhenNotZero);  while GActiveThreadsCount > 0
do    TThread.Sleep(100);end; procedure LaunchThreads;var  i:
SizeInt;begin  TerminateThreads;  Writeln('LaunchThreads'); 
GStopWhenNotZero := 0;  for i := 1 to 3 do   
TThreadOne.Create;end; begin  LaunchThreads;  TThread.Sleep(1000); 
TerminateThreads;  Readln;end.

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torbente · 2021-04-01 20:19

I have to said that it worked perfectly; leaving a small delay makes
that each thread gets a different value from TCounter. This, of
course, is a workoarund only, but could help others to implement an
easy solution for this situations.

I believe that an easy way to do this should be something like..

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
MyThreads[TCounter] := TThreadOne.Create(true);MyThreads[TCounter].Fre
eOnTerminate:=true;MyThreads[TCounter].SetInternalVariable(MySpecialva
riable,1); //or something like thatMyThreads[TCounter].Start;

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Gustavo 'Gus' Carreno · 2021-04-21 20:57

Hey Torbente,

If you define your TThreadOne as so:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i type 
TThreadOne = class(TThread)  private    FMySpecialVariable: Int64; 
protected    procedure Execute; override;  public    property
MySpecialVariable: Int64      read FMySpecialValiable      write
FMySpecialVariable;  end;
You can then do:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i For
TCounter := 1 to 10 do   begin   MyThreads[TCounter] :=
TThreadOne.Create(true);   MyThreads[TCounter].FreeOnTerminate:=true; 
 MyThreads[TCounter].MySpecialVariable:= { Whatever you wanna put here
};   MyThreads[TCounter].Start;   Delay(10);   endend;
And that's for a Read/Write property.

If you want a Read Only, then:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
interfacetype  TThreadOne = class(TThread)  private   
FMySpecialVariable: Int64;  protected    procedure Execute; override; 
public    constructor Create(CreateSuspended: Boolean;
MySpecialVariable: Int64);     property MySpecialVariable: Int64 {
This can be committed if there is no use for it outside the thread } 
   read FMySpecialValiable;  end;implementationconstructor
TThreadOne.CreateSuspended: Boolean; MySpecialVariable: Int64);begin 
inherited Create(CreateSuspended);  FMySpecialVariable:=
MySpecialVariable;end;
And then:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i For
TCounter := 1 to 10 do   begin   MyThreads[TCounter] :=
TThreadOne.Create(true, { The value of MySpecialVariable }); 
 MyThreads[TCounter].FreeOnTerminate:=true; 
 MyThreads[TCounter].Start;   Delay(10);   endend;