better comment

include/amqpcpp/reliable.h

@@ -94,7 +94,8 @@ class Reliable : public BASE
  // get the handler
  auto handler = iter->second;
 
- // remove it from the map
+ // remove it from the map (before we make a call to userspace, so that user space
+ // can add even more handlers, without invalidating iterators)
  _handlers.erase(iter);
 
  // call the ack handler
@@ -130,34 +131,39 @@ class Reliable : public BASE
  // the base-class publish methods for some reason.
  if (iter == _handlers.end()) return BASE::onNack(deliveryTag, multiple);
 
- // call the ack handler
- iter->second->reportNack();
-
- // if the monitor is no longer valid, we stop (we're done)
- if (!monitor) return;
+ // get the handler (we store it first so that we can remove it)
+ auto handler = iter->second;
 
- // erase it from the map
+ // erase it from the map (we remove it before the call, because the callback might update
+ // the _handlers and invalidate the iterator)
  _handlers.erase(iter);
+
+ // call the ack handler
+ handler->reportNack();
  }
 
  // nack multiple elements
  else
  {
- // call the handlers
- for (auto iter = _handlers.begin(); iter != _handlers.end(); iter++)
+ // keep looping for as long as the object is in a valid state
+ while (monitor && !_handlers.empty())
  {
+ // get the first handler
+ auto iter = _handlers.begin();
+
  // make sure this is the right deliverytag, if we've passed it we leap out
  if (iter->first > deliveryTag) break;
 
- // call the handler
- iter->second->reportNack();
+ // get the handler
+ auto handler = iter->second;
+
+ // remove it from the map (before we make a call to userspace, so that user space
+ // can add even more handlers, without invalidating iterators)
+ _handlers.erase(iter);
 
- // if we were destructed in the meantime, we leap out
- if (!monitor) return;
+ // call the ack handler
+ handler->reportNack();
  }
-
- // erase all negatively acknowledged items
- _handlers.erase(_handlers.begin(), _handlers.upper_bound(deliveryTag));
  }
 
  // if the object is no longer valid, return