=head1 NAME

Thread - using wxPerl with threads

=head1 SYNOPSIS

  # the order of these use()s is important
  use threads;
  use threads::shared;
  use Wx;

  my $DONE_EVENT : shared = Wx::NewEventType;

  my $worker = threads->create( \&work );

  # create frames, etc
  my $frame = Wx::Frame->new( ... );
  EVT_COMMAND( $frame, -1, $DONE_EVENT, \&done );
  $app->MainLoop;

  sub done {
      my( $frame, $event ) = @_;

      print $event->GetData;
  }

  sub work {
      # ... do stuff, create a shared $result value

      my $threvent = new Wx::PlThreadEvent( -1, $DONE_EVENT, $result );
      Wx::PostEvent( $frame, $threvent );
  }

  # event handler
  sub OnCreateThread {
      # @_ = () is necessary to avoid "Scalars leaked"
      my( $self, $event ) = @_; @_ = ();

      threads->create( ... );
  }

=head1 DESCRIPTION

Threaded GUI application are somewhat different from non-GUI threaded
applications in that the main thread (which runs the GUI) must never
block.  Also, in wxWidgets, no thread other than the main thread can
manipulate GUI objects.  This leads to a hybrid model where worker
threads must send events to the main thread in order to change the GUI
state or signal their termination.

=head2 Order of module loading

It's necessary for C<use Wx> to happen after <use threads::shared>.

=head2 Sending events from worker threads

C<Wx::PlThreadEvent> can be used to communicate between worker and
GUI threads.  The event can carry a I<shared> value between threads.

  my $DONE_EVENT : shared = Wx::NewEventType;

  sub work {
      # ... do some stuff
      my $progress = new Wx::PlThreadEvent( -1, $DONE_EVENT, $progress );
      Wx::PostEvent( $frame, $progress );

      # ... do stuff, create a shared $result value
      my $end = new Wx::PlThreadEvent( -1, $DONE_EVENT, $result );
      Wx::PostEvent( $frame, $end );
  }

The target of the event can be any C<Wx::EvtHandler>

=head2 Receiving events from worker threads

C<Wx::PlThreadEvent> is a command event and can be handled as such.
The C<< ->GetData >> method can be used to retrieve the I<shared> data
contained inside the event.

  my $DONE_EVENT : shared = Wx::NewEventType;

  EVT_COMMAND( $frame, -1, $DONE_EVENT, \&done );

  sub done {
      my( $frame, $event ) = @_;

      print $event->GetData;
  }

=head2 Creating new threads

Creating new threads from event handlers works without problems except
from a little snag.  In order not to trigger a bug in the Perl
interpreter, all event handler that directly or indirectly cause a
thread creation must clean C<@_> before starting the thread.

For example:

  sub OnCreateThread {
      my( $self, $event ) = @_; @_ = ();

      threads->create( ... );
  }

failure to do that will cause "scalars leaked" warnings from the Perl
interpreter.

=cut