Race condition involving `BiMap.put` and `BiMap.get`, where `get` returns `null` despite no null ever being present in the map.

BiMapRaceCondition.java

package bi_map_race_condition;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

import com.google.common.collect.BiMap;
import com.google.common.collect.HashBiMap;

public class BiMapRaceCondition
{
    public static void main(String[] args)
    {
        // The map in question uses registry keys, but those are ultimately equals-dependent on strings
        // Pre-load it a bit
        final BiMap<String, Object> map = HashBiMap.create();
        for (int i = 0; i < 100; i++)
        {
            map.put("key:" + i, new Object());
        }

        final String key = "special key";
        map.put(key, new Object());

        // We want to see if concurrent calls to map#put can cause map#get to return null
        final long start = System.currentTimeMillis();
        final ExecutorService executor = Executors.newFixedThreadPool(1);
        executor.submit(() -> {
            while (System.currentTimeMillis() < start + 1000)
            {
                map.put(key, new Object());
            }
        });

        while (System.currentTimeMillis() < start + 1000)
        {
            final Object retrievedObject = map.get(key);
            if (retrievedObject == null)
            {
                System.out.println("Race condition!");
            }
        }

        executor.shutdown();
    }
}

Interesting!