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TPythonEngine / TThread
Joined: 24 Apr 2005
Posts: 12
TPythonEngine / TThread
Hi,
I created a TThread-derived class that creates a TPythonEngine instance and
executes Python code. It works fine. If another instance of my derived
thread class is created (after the first one finished and is destroyed),
however, I receive the error: `No engine defined for component ""`.
Here is the code that works the first time, but not the second time it is
called:
Constructor
=========
constructor TXcComThread.Create;
begin
inherited Create(true);
FHtml := TStringList.Create;
FStrings := TStringList.Create;
FPyEngine := TPythonEngine.Create(nil);
FPyEngine.AutoFinalize := False;
FPyEngine.LoadDll;
FPyVar := TPythonDelphiVar.Create(nil);
FPyVar.VarName := `result`;
FPyVar.Engine := FPyEngine;
FPyVar.Initialize;
end;
Destructor
========
destructor TXcComThread.Destroy;
begin
FPyVar.Free;
FPyEngine.Free;
FStrings.Free;
FHtml.Free;
inherited;
end;
I suspect the Python engine and the variable are not properly destroyed when
the thread finishes execution, but the thread`s constructor is called
properly and according to the P4D example code ".Free" seems to be
sufficient.
The exception is thrown when "FPyVar.Initialize" is called:
Call stack
========
TEngineClient.CheckEngine
TPythonType.CreateInstance
TPythonDelphiVar.CreateVar
TPythonDelphiVar.Initialize
I`m properly doing something very wrong ...
Thanks in advance,
-Andreas
Joined: 29 Apr 2005
Posts: 103
TPythonEngine / TThread
Hi Andreas,
I could reproduce the bug with the following code:
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, PythonEngine, StdCtrls;
type
TXcComThread = class(TThread)
protected
FPyEngine : TPythonEngine;
FPyVar : TPythonDelphiVar;
procedure Execute; override;
public
constructor Create;
destructor Destroy; override;
end;
TForm1 = class(TForm)
Button1: TButton;
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
constructor TXcComThread.Create;
begin
inherited Create(True);
FPyEngine := TPythonEngine.Create(nil);
//FPyEngine.AutoFinalize := False;
FPyEngine.LoadDll;
FPyVar := TPythonDelphiVar.Create(nil);
FPyVar.VarName := `result`;
FPyVar.Engine := FPyEngine;
FPyVar.Initialize;
end;
destructor TXcComThread.Destroy;
begin
FPyVar.Free;
FPyEngine.Free;
inherited;
end;
procedure TXcComThread.Execute;
begin
FPyEngine.ExecString(`for i in xrange(10000): pass`);
MessageBeep(0);
end;
procedure TForm1.Button1Click(Sender: TObject);
var
i : Integer;
T : TXcComThread;
begin
for i := 1 to 1000 do
begin
T := TXcComThread.Create;
T.Resume;
T.Free;
end;
end;
end.
There is indeed a problem with a cached TPythonType that was not properly
cleaned up.
I fixed it but then it crashed unless you remove your
FPyEngine.AutoFinalize := False;
Then I could run it several times, but if you run it a lot of times and
watch the memory consumption, you`ll see that it`s leaking a lot.
This is a problem of Python. It`s not well designed for being
initialized/finalized multiple times.
And if you set AutoFinalize to False, it means that P4D won`t finalize
Python and try to reinitialize it the next time. If you don`t finalize
Python, then why would you create several instances of TPythonEngine?
Even if everything`s successful, you`ll have to be very careful with
multithreading as this hasn`t been tested in this context...
So, my advice would be to create a single thread that would queue script
execution requests. Make sure that anything that gets executed by Python
won`t have direct access to VCL objects as they`re not thread safe!
Bye,
Morgan
> -----Original Message-----
> From: pythonfordelphi@yahoogroups.com
> [mailto:pythonfordelphi@yahoogroups.com] On Behalf Of Andreas Schmid
> Sent: April 29, 2005 10:07 AM
> To: pythonfordelphi@yahoogroups.com
> Subject: [pythonfordelphi] TPythonEngine / TThread
>
> Hi,
>
> I created a TThread-derived class that creates a TPythonEngine instance
> and
> executes Python code. It works fine. If another instance of my derived
> thread class is created (after the first one finished and is destroyed),
> however, I receive the error: `No engine defined for component ""`.
>
> Here is the code that works the first time, but not the second time it is
> called:
>
> Constructor
> =========
>
> constructor TXcComThread.Create;
> begin
> inherited Create(true);
> FHtml := TStringList.Create;
> FStrings := TStringList.Create;
>
> FPyEngine := TPythonEngine.Create(nil);
> FPyEngine.AutoFinalize := False;
> FPyEngine.LoadDll;
>
> FPyVar := TPythonDelphiVar.Create(nil);
> FPyVar.VarName := `result`;
> FPyVar.Engine := FPyEngine;
> FPyVar.Initialize;
> end;
>
> Destructor
> ========
>
> destructor TXcComThread.Destroy;
> begin
> FPyVar.Free;
> FPyEngine.Free;
>
> FStrings.Free;
> FHtml.Free;
> inherited;
> end;
>
> I suspect the Python engine and the variable are not properly destroyed
> when
> the thread finishes execution, but the thread`s constructor is called
> properly and according to the P4D example code ".Free" seems to be
> sufficient.
>
> The exception is thrown when "FPyVar.Initialize" is called:
>
> Call stack
> ========
>
> TEngineClient.CheckEngine
> TPythonType.CreateInstance
> TPythonDelphiVar.CreateVar
> TPythonDelphiVar.Initialize
>
> I`m properly doing something very wrong ...
>
> Thanks in advance,
>
> -Andreas
>
>
>
>
>
>
>
>
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>
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