OpenJDK JVM不会在多个核心上调度线程

When I run my multi-threaded Java program on the OpenJDK 6 JVM that is distributed with Ubuntu 12.04, all threads are scheduled on a single core. But when I run the exact same program on the JVM from Oracle's latest 1.7 JDK, it nicely rotates my 20 threads around all 24 available cores. The When I run my multi-threaded Java program on th