RFR: 8073545 - Use shorter and more descriptive names for GC worker threads

Thu Mar 5 13:41:40 UTC 2015

On 2015-03-05, David Lindholm wrote:
> Hi,
> 
> Thanks for your input. To me, threads and tasks are different things. A task
> is something a thread can do for a while, but when it is finished with that
> task it can pick something else to do (another task). This view seems to be
> reflected in gcTaskThread.cpp (the thread for running tasks in
> parallelScavenge). After creation, it runs different tasks managed by
> gcTaskManager. These tasks are called names ending with "task".
> 
> But I agree that in most cases the word Thread is unnecessary (this was why
> I called the Marker Thread "Marker"). But I don't have anything against
> using up all the 15 chars (we should not shorten the name unnecessarily).
> 
> My new suggestion:
> 
> "CMS Thread#xxx"
> "CMS Main Thread"
> "G1 Refine#xxx"
> "G1 Marker#xxx"
> "G1 Main Marker"
> "G1 StrDedup#xxx"
> "ParGC Thread#xx"
> "GC Thread#xxx"

These names looks good to me. I also had a look at the patch and
noticed:
-  set_name("GC task thread#%d (ParallelGC)", which);
+//  set_name("GC task thread#%d (ParallelGC)", which);

Could you please remove the line you commented out?

Thanks,
Erik

> This way our threads naming scheme will be aligned with the rest of the JVM.
> One could argue if '#' is necessary. We could leave it out or print '-'
> instead. The CompilerThreads leave them out.
> 
> 
> Thanks,
> David
> 
> On 2015-03-04 16:24, Bengt Rutisson wrote:
> >
> >Hi David and everyone,
> >
> >Naming is the most difficult part of computer science so I doubt that
> >there is an easy answer here. Given that the names are for debugging I
> >guess it is not too important exactly what the names are. More important
> >is that they are unique. I also think that there is really no need to have
> >"thread" in the name since it is pretty obvious that it is a thread.
> >
> >So, my suggestion would be to skip "thread" and to use CamelCase rather
> >than using spaces to save some characters.
> >
> >I don't have strong opinions on this, but here's what I'd suggest:
> >
> >-      _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS
> >Threads",
> >+      _conc_workers = new YieldingFlexibleWorkGang("CMS Threads",
> >
> >"CMSTask"
> >
> >
> >
> >-  set_name("Concurrent Mark-Sweep GC Thread");
> >+  set_name("CMS Main Thread");
> >
> >"CMSMain"
> >
> >
> >
> >-  set_name("G1 Concurrent Refinement Thread#%d", worker_id);
> >+  set_name("G1 ConRefine#%d", worker_id);
> >
> >"G1ConcRefine#%d"
> >
> >
> >
> >-  _parallel_workers = new FlexibleWorkGang("G1 Parallel Marking Threads",
> >+  _parallel_workers = new FlexibleWorkGang("G1 Markers"
> >
> >"G1MarkTask"
> >
> >
> >
> >-  set_name("G1 Main Concurrent Mark GC Thread");
> >+  set_name("G1 Main Marker");
> >
> >"G1ConcMark"
> >
> >
> >
> >-  set_name("String Deduplication Thread");
> >+  set_name("StrDedup Thread");
> >
> >"StringDedup"
> >
> >
> >
> >-  set_name("GC task thread#%d (ParallelGC)", which);
> >+  set_name("ParGC Thread#%d", which);
> >
> >"ParGCTask"
> >
> >
> >
> >-    _workers = new FlexibleWorkGang("Parallel GC Threads",
> >ParallelGCThreads,
> >+    _workers = new FlexibleWorkGang("GC Threads", ParallelGCThreads,
> >
> >"GCParTask"
> >
> >
> >Just my thoughts. And regarding having 3 characters left for the number in
> >the thread name I don't know if that is too important. With the above
> >suggestions this will be possible in most cases but not all. Personally I
> >think that is good enough.
> >
> >Bengt
> >
> >
> >On 2015-03-04 15:11, David Lindholm wrote:
> >>Hi Jesper,
> >>
> >>On 2015-03-04 14:52, Jesper Wilhelmsson wrote:
> >>>Hi David,
> >>>
> >>>Thanks for fixing this!
> >>>
> >>>A couple of questions:
> >>>
> >>>-  set_name("G1 Concurrent Refinement Thread#%d", worker_id);
> >>>+  set_name("G1 ConRefine#%d", worker_id);
> >>>
> >>>Is there any refinement threads that are not concurrent? If not, could
> >>>we just call this "G1 Refine#%d" to simplify it slightly and remove an
> >>>implementation detail that doesn't need to be exposed? This would also
> >>>leave room for three digit numbers in case we have lots of these
> >>>threads on some systems.
> >>
> >>I discussed this with Bengt, and his input was that Concurrent
> >>Refinement is a well known concept in G1. I have no real opinion here,
> >>I'm fine with both suggestions.
> >>
> >>>-  _parallel_workers = new FlexibleWorkGang("G1 Parallel Marking
> >>>Threads",
> >>>+  _parallel_workers = new FlexibleWorkGang("G1 Markers",
> >>>
> >>>Markers is cute, but could be misunderstood. Can we call it "G1 Mark
> >>>Threads" instead?
> >>
> >>No, it is too long, the three last character with thread number won't
> >>fit (#xx).
> >>
> >>>-  set_name("G1 Main Concurrent Mark GC Thread");
> >>>+  set_name("G1 Main Marker");
> >>>
> >>>Again, "Marker" could be misunderstood. I don't have a good
> >>>replacement though.
> >>
> >>I'm open for suggestions, but I think "G1 Main Marker" works.
> >>
> >>>-  set_name("GC task thread#%d (ParallelGC)", which);
> >>>+  set_name("ParGC Thread#%d", which);
> >>>
> >>>I don't have a good suggestion for how to make this one character
> >>>shorter, but currently there is only room for two digit numbers. Maybe
> >>>just "GC Thread#%d". I don't think these threads will exist at the
> >>>same time as any other GC threads anyway.
> >>
> >>With your suggestion these threads would be called the same thing as the
> >>threads in sharedHeap. I think it is nice to quickly be able to see that
> >>these threads indeed belongs to the ParallelGC.
> >>
> >>>-  set_name("Gang worker#%d (%s)", id, gang->name());
> >>>+  set_name("%s#%d", gang->name(), id);
> >>>
> >>>Is there any limitation on the length of the name()? If it's too long
> >>>the number won't show. Can we add an assert to make sure it isn't too
> >>>long?
> >>
> >>I have gone through our current GangWorkers, and they fit. If you want I
> >>can add an assert for <= 12 characters. OTOH it is not the end of the
> >>world if we don't see the whole number in the debugger.
> >>
> >>
> >>Thanks,
> >>David
> >>
> >>>
> >>>Thanks,
> >>>/Jesper
> >>>
> >>>
> >>>David Lindholm skrev den 4/3/15 13:48:
> >>>>Hi,
> >>>>
> >>>>Please review this small fix which changes the names of the GC
> >>>>threads to be
> >>>>shorter and more descriptive. There is a limit on 16 characters
> >>>>including the
> >>>>terminating null byte for this name, since pthread_set_name_np() is
> >>>>used. This
> >>>>change will make it easier to debug, as these names shows up in the
> >>>>debugger.
> >>>>
> >>>>Webrev: http://cr.openjdk.java.net/~brutisso/8073545/webrev.00/
> >>>>Bug: https://bugs.openjdk.java.net/browse/JDK-8073545
> >>>>
> >>>>Testing: Passed JPRT.
> >>>>
> >>>>
> >>>>Regards,
> >>>>David
> >>
> >
> 