Maintains codec event counts, for debugging purposes only.
Counters should be written from the playback thread only. Counters may be read from any thread.
To ensure that the counter values are correctly reflected between threads, users of this class
should invoke ensureUpdated() prior to reading and after writing.
Should be invoked from the playback thread after the counters have been updated. Should also
be invoked from any other thread that wishes to read the counters, before reading. These calls
ensure that counter updates are made visible to the reading threads.