When available Coherence will utilize either sun.misc.AtomicLong or java.util.concurrent.atomic.AtomicLong (1.5 only) to implement concurrent counters. If neither of these is available Coherence will use a somewhat less performant synchronized counter, and output the following warning.
Though it is safe to ignore this message, if possible it may be best to address it.
If you are using a Sun 1.4 or higher JVM, simply running the JVM in server mode allows the use of the concurrent counter, as well as providing a number of other JVM performance improvements associated with the server JVM setting. Server mode can be specified by including "-server" on the JVM command line.
If using a non-Sun JVM, upgrading to the vendor's 1.5 or higher JVM will allow support for concurrent counters.