simgear/props/props_test.cxx: test for self-unregister.
SGPropertyNode::removeChangeListener() used to modify the _listeners vector or
even delete it and set _listeners to NULL, if a listener was removed.
This could cause a SEGV if removeChangeListener() was called from
a listener, because listeners are called from methods such as
SGPropertyNode::fireValueChanged() which iterate through _listeners and don't
expect it to be changed to NULL.
The fix here is to keep a track of whether we are iterating through the
_listeners vector; if we are, SGPropertyNode::removeChangeListener() sets the
entry to NULL, instead of removing it.
We have a new internal function forEachListener() which takes
care of the iterating details - incrementing/decrementing the new
_listeners->_num_iterators count and skipping NULL entries. Before returning,
if _num_iterators is now zero it removes any NULL entries in the vector of
listeners.
The nListeners() member is no longer inline, because it needs to ignore NULL
entries in the vector. And _listeners now points to an internally-defined
struct which contains a new _num_iterators as well as the vector of listeners.
Added self-unregister test to simgear/props/props_test.cxx.
1d978429f5