RFR: JDK-8240340: java/lang/management/ThreadMXBean/Locks.java is buggy

[Alex Menkov]

Hi David,

Thanks you for the review.

On 03/04/2020 17:50, David Holmes wrote:
> Hi Alex,
> 
> On 5/03/2020 10:30 am, Alex Menkov wrote:
>> Hi all,
>>
>> please review the fix for
>> https://bugs.openjdk.java.net/browse/JDK-8240340
>> webrev:
>> http://cr.openjdk.java.net/~amenkov/jdk15/ThreadMXBean_Locks_test/webrev/
>>
>> changes:
>> - assertThreadState method: don't re-read thread state throwing 
>> exception (as we got weird error like "Thread WaitingThread is at 
>> WAITING state but is expected to be in Thread.State = WAITING");
>> - added proper test shutdown on error (made all threads "daemon", 
>> interrupt waiting thread if CheckerThread throws exception);
>> - if CheckerThread detects error, propagate the exception to main thread;
> 
> The test changes seem fine.
> 
>> - fixed LockFreeLogger class - it should work for logging from several 
>> threads, but it doesn't. I prefer to simplify it just to keep 
>> ConcurrentLinkedQueue<String>.
>> LockFreeLogger is also used by ThreadMXBeanStateTest test, but only by 
>> a single thread.
> 
> I don't understand your changes here as you've completely changed the 
> intended design of the logger. The original accumulates log entries 
> per-thread and then spits them all out (though I'm not clear on the 
> exact ordering - I don't how to read that stream stuff). The new code 
> just creates a single queue of log records interleaving entries from 
> different threads. The simple logger may be all that is needed but it 
> seems quite different to the intent of the original.

Testing changes in the test I discovered that there is something wrong 
with the logger - it printed only part of the records, so I have to look 
at the LockFreeLogger class and I don't understand how it was supposed 
to work.
About ordering in cumulative log: each record has Integer which used to 
sort log entries from all threads (i.e. records from different threads 
are printed at the order which log() was called).
Looking at allRecords/records stuff I don't understand how it should be 
used. To get logs from different threads in one logger, we needs one 
instance. So we create LockFreeLogger (in main thread) and ctor creates 
ThreadLocal record and register it in allRecords. Logging from main 
thread works fine, but if any other thread tries to log, 1st log() call 
creates its own ThreadLocal records (by records.get()) and log records 
from this thread go there. But this ThreadLocal records is not 
registered in allRecords, so this logging won't be included in final log.
Looks like we need to change log() to something like

Map<Integer, String> recs = records.get();
if (recs.isEmpty()) {
     allRecords.add(recs);
}
recs.put(id, String.format(format, params));

But all this stuff do exactly the same as simple ConcurrentLinkedQueue 
(i.e. lock free ordered list).
At least I don't see other rationale in the stuff.

--alex

> 
> Thanks,
> David
> 
>> --alex