Doubled methods are shown in jstack output on Solaris/Sparc when SA mechanism is used, namely jstack is run with options -m and -F.

Testcase
public class Test {
   public static void main(String[] args) {
        try {
            while (true) Thread.sleep(1000);
        } catch (Exception e2) { } }
}

output of jstack -F
....
Thread t@7: (state = BLOCKED)
- java.lang.Object.wait(long) @bci=679454459 (Interpreted frame)
- java.lang.Object.wait(long) @bci=0 (Interpreted frame)
- java.lang.ref.ReferenceQueue.remove(long) @bci=44, line=134 (Interpreted frame)
- java.lang.ref.ReferenceQueue.remove() @bci=2, line=150 (Interpreted frame)
- java.lang.ref.Finalizer$FinalizerThread.run() @bci=3, line=177 (Interpreted frame)

....
Thread t@2: (state = BLOCKED)
- java.lang.Thread.sleep(long) @bci=0 (Interpreted frame)
- java.lang.Thread.sleep(long) @bci=0 (Interpreted frame)
- Test3.main(java.lang.String[]) @bci=22, line=8 (Interpreted frame)