[Monotone-devel] set's erase() and iterators

[Markus Schiltknecht]

Hello Will,

on my box, monotone's suspend test reproducibly failed. Today I've 
tracked down the bug, which took me quite some time.

When erasing from a set<>, most iterators remain valid, except the one 
you've just erased (of course!). But that in turn means, that the 
following code in project.cc could lead to a segmentation fault 
(probably also dependent on the STL implementation):

  for(std::set<revision_id>::iterator it = branch.second.begin();
      it != branch.second.end(); ++it)
    if (some_decision_func(...))
      branch.second.erase(*it);

It's one of the less obvious things in the STL, and about everybody has 
stumbled over it before, at least I did already several times ;-)

One option to circumvent that problem is recreating the set, as I did 
for project.cc now. Another option might be using the STL algorithm 
remove_if().

Regards

Markus