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Showing posts from August, 2012

Which Java thread consumes my CPU?

What do you do when your Java application consumes 100% of the CPU? Turns out you can easily find the problematic thread(s) using built-in UNIX and JDK tools. No profilers or agents required. For the purpose of testing we'll use this simple program: public class Main { public static void main(String[] args) { new Thread(new Idle(), "Idle").start(); new Thread(new Busy(), "Busy").start(); } } class Idle implements Runnable { @Override public void run() { try { TimeUnit.HOURS.sleep(1); } catch (InterruptedException e) { } } } class Busy implements Runnable { @Override public void run() { while(true) { "Foo".matches("F.*"); } } } As you can see, it starts two threads. Idle is not consuming any CPU (remember, sleeping threads consume memory, but not CPU) while Busy eats the whole core as regular expression parsing and executing