Re: Octave/backend synchronization

[Michael Goffioul]

On 1/25/08, John W. Eaton <address@hidden> wrote:
> | 1) it's the responsbility of any C++ code (typically a graphics backend)
> | to lock/unlock the graphics system when this is required; for instance,
> | a rendering event handler would look like
> |
> | void handle_draw_event (draw_event *evt)
> | {
> |   gh_manager::lock ();
> |
> |   // Do all rendering stuff
> |
> |   gh_manager::unlock ();
> | }
>
> I think the problem with this is that it would be easy to forget, and
> then hard to debug.

One final note maybe (before closing the subject). While implementing
auto-locking in the set_X/get_X methods seems easier, it only avoids
local problems. For instance it does not guarantee that 2 get_X calls
within the same function body will return the same value. For
instance, consider the following code executed in a separate thread:

void my_function (void)
{
  ...
  x = props.get_X ();

  // do something

  x = props.get_X ();
  ...
}

The second get_X call might return something different, if another
thread has call set_X in between. One workaround is to cache the
returned value from the first call, but you have to know it...
However, I admit this is a kind of corner case.

Michael.