Accurately Calculating the time a Thread takes to run

How do I accurately gain timings for a thread? I have a number of threads which are calling CalculatorEngine which locks on an object starts a timer (ctime = System.currentTimeMillis();) and then logs the time just before the thread exits

System.out.println("Calculations for " + setName + " for " + calcsMadeByCalcEnginge + " positions took: " + (System.currentTimeMillis() - ctime));

But if there is a context swich my timer will continue to run until the thread is reactivated and then completes... How can I gain the actual timings for how long the thread took?

[585 byte] By [java_swing_dudea] at [2007-11-27 11:44:43]