Re: [wxperl-users] Threads

[Mark D. <mar...@zn...>]

Hi,

I think 2 - cloning the C++ objects is probably just about the best
option. I can imagine the possibility of a situation where it might be
of some use for a thread to get a copy of a parent object and go to work
on that in the background.

Having said that, I would not choose 2 if that option represented much
more work than 1 or 3.

As there's no clear obvious choice, I think whichever option is easiest
for you to implement.

I assume we are only concerned with the listed object types and that
with any of the options, the following code in a secondary thread would
still work (I'm concerned about using Wx::Window::FindWindowById in the
context shown below)

my $WINDOW_ID = (the ID of a window in my main gui thread);
my $window = Wx::Window::FindWindowById($WINDOW_ID, undef);
my $newevent = Wx::PlThreadEvent->new( -1, $MY_EVENT_ID, $sharedvar );
Wx::PostEvent( $window, $newevent );

Regards

Mark


Mattia Barbon wrote:
>   Hi all,
> the topic is abviously threads. This program:
> 
> ==========
> #!/usr/bin/perl -w
> 
> use strict;
> use warnings;
> use threads;
> use Test::More tests => 4;
> 
> use Wx;
> 
> my $app = Wx::App->new( sub { 1 } );
> my $color = Wx::Colour->new( 0, 10, 20 );
> 
> use Devel::Peek;
> 
> my $t = threads->create
>   ( sub {
>         ok( 1, 'In thread' );
>     } );
> ok( 1, 'Before join' );
> $t->join;
> ok( 1, 'After join' );
> 
> END { ok( 1, 'At END' ) };
> =========
> 
> crashes after test 3 (after join). The reason is that when the thread is
> started the perl-space variables are cloned, but the C++-space objects
> are not, so bot threads think they hold the last reference to $color,
> both try to free the underlying C++ object => segmentation fault.
> 
>   There are various way to work around this; all involve keeping tracks
> of created objects (Wx::Colour instances in this case) and doing something
> special at clone time. This solves the problem once you decide what
> special action you want to take.
> 
>   Options:
> 1 - the new thread is denied access to the parent thread objects
>     (tried and works; you should not access wxThings from multiple
>      threads anyway)
> 2 - clone the C++ instances; for each variable do (more or less)
>     $var = Wx::Colour->new( $var );
> 3 - give the new thread access to the original thread's C++ objects
>     avoiding the double free (i.e. do what happens now, except for the
>     segfault).
> 4 - other options?
> 
>   Any suggestions?
> 
> Thanks!
> Mattia
> 
>   The list of classes needing special treatment is:
> Wx::DataObject
> Wx::DropTarget
> Wx::FileSystem
> Wx::FSFile
> Wx::GridCellAttr
> Wx::GridCellAttr
> Wx::GridCellEditor
> Wx::GridCellRenderer
> Wx::HtmlEasyPrinting
> Wx::Printer
> Wx::XmlResource
> Wx::Accelerators
> Wx::Bitmap
> Wx::Brush
> Wx::Cursor
> Wx::Font
> Wx::Icon
> Wx::Image
> Wx::ImageList
> Wx::Locale
> Wx::Palette
> Wx::Pen
> 
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