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LinkedLruHashMap: Bad state when remove() removes the last entry #385

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hugovangalen opened this Issue Nov 16, 2017 · 2 comments

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hugovangalen commented Nov 16, 2017

My own code crashed in the method _removeLru with a null pointer access when calling _tail.next.

After debugging I discovered that the cause seems to be in the remove() method.

There exists a check whether the removed entry is equal to _head, or it is equal to _tail.

If it happens to be the last item that gets removed, that is not handled correctly. Right now it branches into the entry == _head, resets _head, but leaves _tail in its old value, which is wrong.

If my understanding is correct, in that case both _tail and _head need to be reset to null. Adding a test for entry == _head && entry == _tail to reset the _tail and _head to null appears to fix the problem:

  @override
  V remove(Object key) {
    final entry = _entries.remove(key);
    if (entry != null) {
      if (entry == _head && entry == _tail) {
        _head = null;
        _tail = null;
      } else if (entry == _head) {
        _head = _head.next;
      } else if (entry == _tail) {
        _tail.previous.next = null;
        _tail = _tail.previous;
      } else {
        entry.previous.next = entry.next;
      }

      return entry.value;
    }
    return null;
  }
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cbracken Nov 16, 2017

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Fixed by #386 and released in v0.26.1. Thanks for diagnosing and reporting this!

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cbracken commented Nov 16, 2017

Fixed by #386 and released in v0.26.1. Thanks for diagnosing and reporting this!

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hugovangalen Mar 23, 2018

@cbracken No problem. I'd like to stress that there are still issues with dangling references. See ticket #412.

hugovangalen commented Mar 23, 2018

@cbracken No problem. I'd like to stress that there are still issues with dangling references. See ticket #412.

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