Github user AlexShvedoff commented on the issue:
https://github.com/apache/metamodel/pull/175
It doesn't look like .add is threadsafe. Per the ArrayList overview docs,
you might be left with the impression that as long as sufficient max capacity
has been pre alloc'd you're thread-safe. But if you look at the implementation
of .add:
457 public boolean More ...add(E e) {
458 ensureCapacityInternal(size + 1); // Increments modCount!!
459 elementData[size++] = e;
460 return true;
461 }
That elementData[size++] is definitely not atomic, so it's possible for
concurrent threads to step on each other and overwrite the same array slot.
But yeah, we are ok here since the ArrayList being used is definitely not
shared between threads.
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