Weird behaviour encapsulated std::list in std::vector sometimes - c++

Question

I am working on a RTS game. This game has buildings and actors. A building or actor is an instance of the buildings or actors class. These instances are stored in a std::vector for easy interaction by iterator id.
The actors and buildings can do tasks, these are stored in an std::list instantiated by the class in other words that list lives inside std::vector<actors>. The problem now is that every so often when information about this tasks needs retrieval or the tasks has to be removed from the list the program will crash with either "access violation", "trying to pop_front on empty list" or "trying to call front() on a empty list". Even though the previous line of code was a double check to see if the list was indeed not empty! It is also hard to reproduce because it happens every so often.
I suspect that someway somehow iterators or pointers get invalidated, since the list lives in a vector. I tried circumventing that by reserving space for 1600 units and 1600 buildings. However the problem still persists.
if (!this->listOfOrders.empty()) {
switch (this->listOfOrders.front().orderType) { //error here calling front() on empty list
case stackOrderTypes::stackActionMove:
this->updateGoal(this->listOfOrders.front().goal, 0);
break;
case stackOrderTypes::stackActionGather:
this->updateGoal(this->listOfOrders.front().goal, 0);
this->setGatheringRecource(true);
break;
}
}
I am really at a loss here.
Simplified class construct to illustrate:
enum class stackOrderTypes
{
stackActionMove,
stackActionGather
//and so on...
};
struct goal
{
int x;
int y;
}
struct orderStack
{
cords goal;
stackOrderTypes orderType;
};
class actors
{
public:
//other functions here
void doNextStackedCommand();
void stackOrder(cords Goal, stackOrderTypes orderType);
private:
//other stuff goes here
std::list<orderStack> listOfOrders;
};
std::vector<actors> listOfActors; //all actors live in here

Answer 1

To know what problem is causing this error, you need first to find exactly where in your code the problem is happening.
However, from what you describe I see a possible cause of you problem : items removals.
I suppose you have some loops iterating over your orders, and under some conditions you remove orders from your order list. Check if your code looks like this :
for (auto it = orderList.begin(); it != orderList.end(); ++it)
{
// Some code there
if (OrderIsFinished() == true)
orderList.erase(it);
// Some code there
}
This is a common mistake. After calling erase, the item pointed by the iterator it gets removed and it is invalidated. To keep iterators consistent after a removal, you need to change the way you iterate through all elements :
auto it = orderList.begin();
while (it != orderList.end())
{
// Some code there
if (OrderIsFinished() == true)
it = orderList.erase(it);
else
++it;
}

Answer 2

It was in fact a data race issue. There was a std::async updater running for builds while the update function was also called in the main thread!