On Feb 27, 2009, at 6:10 AM, Stamenkovic Florijan wrote:
On Feb 26, 2009, at 22:22, Chuck Hill wrote:
<snip>
I am old. My memory is weak. Less snips help.
How? Where?
willRead(), willReadRelationship(Object)
<snip>
Have stack traces?
See below. Sorry about not providing them before, that was silly.
How come this particular exception happens in a multi-threaded
scenario and not in a single threaded scenario?
Hint: more than one thread. :-) Concurrency
woooow, ya think? :-P
Dunno, just a guess. ;-)
(Also note that the lock object is not public, it's lock() and
unlock() methods are exposed through the public API of
EODistributedObjectStore). Assuming that ReenetrantLock is not
buggy, the only way I can imagine to get this exception is doing
the equivalent of:
if(accessingThreadCount > 1) // super-evil
eoDistributedObjectStoreInstance.unlock();
If anyone else knows another way, please let me know. I can't
think of one, and am amazed to see it happening.
In the meanwhile, I admit defeat, and go back to single threaded
EOF operations.
An exception resulting in an unlock upon which the other thread
locks it and then a finally block unlocking it again in the first
thread?
Interesting idea, however... Let's say that this exception you
mention gets thrown in a single threaded scenario. It would still
result in more calls to unlock() then to lock(). The
IllegalMonitorStateException would be thrown at either of the last
two unlock() calls. So, we can assume it does not happen in a single
threaded scenario, since the monitor exception is not thrown.
You would get a different error (attempt to unlock an unlocked lock?)
if ReentrantLock even throws on that condition.
Which means that it only happens in a multi threaded scenario. So,
it still falls under the category of the idiotic idiom:
if(accessingThreadCount > 1)
throw SomeException();
Or not?
I still rather doubt that. :-)
Output logged from my EC's lockObjectStore() and unlockObjectStore()
methods. There is only one EC.
...
will lock: JBND worker thread
did lock: JBND worker thread
will unlock: JBND worker thread
did unlock: JBND worker thread
will lock: AWT-EventQueue-0
did lock: AWT-EventQueue-0
will lock: JBND worker thread
did lock: JBND worker thread
will unlock: AWT-EventQueue-0
did unlock: AWT-EventQueue-0
will unlock: JBND worker thread
I am not sure what that means. Also be careful of messages output by
a log mechanism in a MT environment. NSLog in particular will show
things out of exact order.
Stack traces... Got them by putting an exception breakpoint for
IllegalMonitorStateException. The breakpoint set to suspend the VM.
Traces are from the only two threads that do EOF work:
Thread [JBND worker thread] (Suspended (exception
IllegalMonitorStateException))
ReentrantLock$NonfairSync(ReentrantLock$Sync).tryRelease(int) line:
125
ReentrantLock$NonfairSync(AbstractQueuedSynchronizer).release(int)
line: 1137
ReentrantLock.unlock() line: 431
EODistributedObjectStore.unlock() line: 107
JCEC(EOEditingContext).unlockObjectStore() line: 4668
JCEC.unlockObjectStore() line: 283
User(EOFDataObject).willRead() line: 744
_EOMutableKnownKeyDictionary$Initializer
$_GenericRecordBinding.valueInObject(Object) line: 570
User(EOCustomObject).storedValueForKey(String) line: 1634
User(_User).password() line: 77
...
Thread [AWT-EventQueue-0] (Suspended)
JCEC.lockObjectStore() line: 274
Account(EOFDataObject).willRead() line: 742
_EOMutableKnownKeyDictionary$Initializer
$_GenericRecordBinding.valueInObject(Object) line: 570
Account(EOCustomObject).storedValueForKey(String) line: 1634
Account(_Account).number() line: 94
GeneratedMethodAccessor50.invoke(Object, Object[]) line: not
available
DelegatingMethodAccessorImpl.invoke(Object, Object[]) line: 25
Method.invoke(Object, Object...) line: 585
NSKeyValueCoding$ValueAccessor$1.methodValue(Object, Method) line:
636
NSKeyValueCoding$_MethodBinding.valueInObject(Object) line: 1134
Account(EOCustomObject).valueForKey(String) line: 1498
Account(EOFDataObject).valueForKey(String) line: 714
Account(EOFDataObject).get(String) line: 212
...
That is a lot of locks. Is there any chance that the order of locking
and unlocking is different somewhere? Not sure how that would cause
this error...
Chuck
--
Chuck Hill Senior Consultant / VP Development
Practical WebObjects - for developers who want to increase their
overall knowledge of WebObjects or who are trying to solve specific
problems.
http://www.global-village.net/products/practical_webobjects
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