[Proposal/Question] Provide mechanism to monitor thread states more efficiently

[mandy chung]

serviceability-dev is the mailing list for discussing 
java.lang.management APIs.

Getting the stack trace is expensive. ThreadMXBean.getThreadInfos(ids) 
does not get the stack trace and locks information and is less expensive.

A typical lightweight monitoring application does BCI and call 
Thread::getState and collect all other monitoring data.

Mandy

On 10/27/17 8:23 AM, Christoph Dreis wrote:
> Hey,
>
> I don't know if this is the correct mailing list for this specific topic.
> Please let me know in case it isn't.
>
> I'm currently trying to improve the live-monitoring of an application and
> would like to get a simple overview of how many threads are in state
> RUNNABLE, BLOCKED and so on.
> For this I need to get all threads in the first place to iterate on. I know
> of two ways how to do that programmatically:
>
> 1) ThreadMXBean.dumpAllThreads() which gives me an array of ThreadInfo
> objects on which I could call getThreadState()
> 2) Thread.getAllStackTraces().keySet() which gives me a Set of Thread
> objects on which I could call getState()
>
> Either 1) or 2) both dump the threads, which seems like a lot of overhead
> for this task and therefore presumably aren't supposed to be executed every
> X seconds. Using reflection to make the private native Thread.getThreads()
> available - if that's even possible(?) - doesn't seem correct either. Is
> there an alternative for this?
>
> If not, I'd like to suggest the addition of two in my opinion more
> lightweight alternative APIs in Thread and/or ThreadMXBean (ThreadImpl).
> Here is what I'm thinking of in a rough and untested state:
>
> 	public static Map<Thread.State, Integer> getAllThreadStateCounts() {
> 		// Get a snapshot of the list of all threads
> 		Thread[] threads = getThreads();
> 		Map<Thread.State, Integer> m = new
> EnumMap<>(Thread.State.class);
> 		for (int i = 0; i < threads.length; i++) {
> 			m.merge(threads[i].getState(), 1, Integer::sum);
> 		}
> 		return m;
> 	}
>
> 	public static int getThreadCountByState(Thread.State state) {
> 		// Get a snapshot of the list of all threads
> 		Thread[] threads = getThreads();
> 		int counter = 0;
> 		for (int i = 0; i < threads.length; i++) {
> 			if (state == threads[i].getState()) {
> 				counter++;
> 			}
> 		}
> 		return counter;
> 	}
>
>
> Is this something that could be worthwhile? Let me know what you think.
>
> Cheers,
> Christoph
>

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