Thread-safe access to graphic objects - proposal

[Maciek Gajewski]

Driss Ghaddab wrote

Event when properties are only read, they have to be protected by mutex, to 
retain consistency ant to keep them from being deleted in another thread.

Maciek Gajewski

> To set an object property, there are four cases:
> - octave thread can set the value, but it needs to protect from mutual
> access (i.e. the GUI thread may modify the value, thus the mutex);
> - octave thread can set the value, but it does not need to protect from
> mutual access (i.e. the GUI thread never modifies that value)
> - octave thread is not allowed to modify the value and delegates the
> task to the GUI thread,
> - or, the property is read only and it is not allowed to modify it.