Cleaner queue monitoring

After some time off this little projects and more thoughts, I returned with much cleaner and simpler design for queue monitor. We are still keeping thread-local map of counters. However, they are not aggregated from the same threads. Instead, we create a registry of such maps. Every entry in the registry is keyed by a phantom reference to another thread-local object. This allows cleaning up the registry in the case when threads are disappearing. All statistics, gathered from disappeared threads, is accumulated in a special "deads" map.
Every specified interval of time, a timer thread is iterating through the registry and calculates aggregated monitored values. It also takes into account "deads" map and cleans up registry entries for the dead threads, if necessary.
This time, I decided to observe only 2 values: Size of Distribution Queue and size of all Output Queues.
Here is the console output of the test program and resulting graph:

Publish rate: 77942.3226812159
Average delay: 1471 ms
Max delay: 2680 ms
Received: 100000 messages
Publish rate: 43047.78303917348
Average delay: 1854 ms
Max delay: 3772 ms
Received: 100000 messages
Publish rate: 51435.18518518518
Average delay: 2169 ms
Max delay: 4338 ms
Received: 99990 messages
Publish rate: 56116.72278338945
Average delay: 2866 ms
Max delay: 6050 ms
Received: 100000 messages
Publish rate: 47483.38081671415
Average delay: 2987 ms
Max delay: 6108 ms
Received: 100000 messages
Publish rate: 48219.97105643994
Average delay: 3192 ms
Max delay: 6768 ms
Received: 99960 messages
Publish rate: 47873.5632183908
Average delay: 3230 ms
Max delay: 6775 ms
Received: 99960 messages
Publish rate: 31645.569620253165
Average delay: 4531 ms
Max delay: 8746 ms
Received: 100000 messages
Publish rate: 39615.68938193344
Average delay: 5171 ms
Max delay: 10623 ms
Received: 99990 messages
Publish rate: 49188.391539596654
Average delay: 5008 ms
Max delay: 10190 ms
Received: 100000 messages