TryRemove(KeyValuePair<K, V>) removes item even when value doesn't match

[mobratil]

I was investigating the code of TryRemove(KeyValuePair<K, V>) and found a race condition.
Under certain circumstances the item is removed even when value doesn't match.

Here is the reproduction code:

using BitFaster.Caching;
using BitFaster.Caching.Lru;

var cache = (ICacheExt<int, string>)new ConcurrentLru<int, string>(capacity: 100);

Task.Run(() =>
{
    for (;;)
    {
        cache.TryRemove(new KeyValuePair<int, string>(5, "x"));
    }
});

for (var i = 0; i < int.MaxValue; i++)
{
    cache.AddOrUpdate(5, "a");
    if (!cache.TryGet(5, out _))
    {
        throw new Exception("My value is gone :-("); // This should not happen, we are only removing (5, "x")
    }

    cache.AddOrUpdate(5, "x");
}

I believe this shouldn't be expected. I kindly ask for confirmation.

[bitfaster]

Thanks for reporting - yes, this is a bug. Fix is checked in and will ship in next version.