alist: fix race condition while iterating#1859
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BareosBot merged 10 commits intobareos:masterfrom Jul 19, 2024
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I think we should preserve the ability to loop over a NULL alist<T>*. We just need free function templates for that which will also eliminate the need to dereference the alist<T>* before giving it to for().
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Great work! It is incredible how much simpler a lot of the code suddenly looks with just that simple change...
As alists mutated themselves when iterated over, it was not safe to even iterate over them from multiple threads at the same time. This lead to hard to debug bugs. This commit changes the foreach_alist macro in such a way that it does not rely on the internal iterator state any longer and instead uses a simple pointer pair.
The foreach_alist macro used to take care of nullchecks, which our range-based for loop does not do on its own. As such we need to add it back manually.
We can instead use the alist* iterators that automatically check for null.
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This pr fixes a race condition that happens when iterating over the same alist concurrently. This is done by rippping out the internal iterator state and using extrernal ones. Specifically we now use a simple pointer pair similar to std::vector.
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