tl;dr I think you are running into GC-related behavior, where threads are being put in waiting state to allow for garbage collection. I do not have the whole truth but I hope to provide some pieces of insight. First thing to realize is that the number in brackets, [0x00007fe64df9a000], is not the address of a … Read more
TL;DR: write locks appear in the “ownable synchronizers” list, read locks don’t. I ended up with the following MVCE to try and understand what’s with “ownable synchronizer”. The idea was to have two threads locking/unlocking read/write reentrant locks and see the effect on different thread dumps at different timings (taken in jVisualVM while the Eclipse … Read more
You will get “waiting to lock” in the thread dump when using intrinsic locks and “parking to wait for” when using locks from java.util.concurrent. Consider the following example: import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock; public class LockTest { final Lock lock = new ReentrantLock(true); synchronized void intrinsicLock() { Thread th = new Thread(new Runnable() { public void … Read more
I got it working by doing two things: Changed call to: sudo -u tomcat6 jstack -J-d64 -m pid Replaced OpenJDK with Sun’s original sun-6-jdk and sun-6-jre packages Explanation for part 1: I switched to 64-bit mode, used sudo and run the command as Tomcat user. Note: Part 2 might not be necessary. For some users … Read more
I know this is an old question but I just wrote a tool to help make long thread dumps more readable. Java Thread Dump Analysis Tool This tool groups threads together which have the same stack trace and allows you to only show threads which are in particular states (e.g. RUNNABLE or BLOCKED). This makes … Read more
A thread dump is a dump of the stacks of all live threads. Thus useful for analysing what an app is up to at some point in time, and if done at intervals handy in diagnosing some kinds of ‘execution’ problems (e.g. thread deadlock). A heap dump is a dump of the state of the … Read more
The TID is thead id and NID is: Native thread ID. This ID is highly platform dependent. It’s the NID in jstack thread dumps. On Windows, it’s simply the OS-level thread ID within a process. On Linux and Solaris, it’s the PID of the thread (which in turn is a light-weight process). On Mac OS … Read more
You can use jmap to get a dump of any process running, assuming you know the pid. Use Task Manager or Resource Monitor to get the pid. Then jmap -dump:format=b,file=heap.hprof <pid> to get the heap for that process. For systems where bash and pgrep are installed and a single Java process is running, try: jmap … Read more