RFR(M): 8069412 : Locks need better debug-printing support

[Vladimir Kozlov]

On 2/13/15 5:33 AM, David Chase wrote:
>> In general I am fine with this changes. There are styles issues, indention (used 4 bytes instead of 2). Other then that I have only few comments.
>
> markOop.cpp?  Fixed it.

Also basicLock.cpp and vframe.cpp. They also miss {} for new if statements.

> LogCompilation files are java and 4-character indent by default.
>
>> In vframe.cpp why you cloned print_locked_object_class_name() to all passes. Instead you could set Boolean local in inner scope if you want to print Verbose output after print_locked_object_class_name().
>
> "mark" was not in scope outside, it seemed cleaner on balance just to clone the call.

You can set 'markOop mark = NULL' before 'if (!found_first_monitor' and use 'if (Verbose && (mark != NULL))' condition 
to print additional info. I don't think to have 3 copy of code is clean.

>
>> Also I don't think you need "_debug" in then name LockNode::is_nested_lock_region_debug().
>
> I wanted it to be clear that this was only for debugging -- it is clone of the previous method with tracing in the failure paths.

Why duplicate code that to do logging. Note, the logging is available in product VM too. I would suggest to modify the 
original method to do logging. You can pass additional bool argument to trigger logging if you don't want to do it always.

>
>> You only need to add additional check is_Lock() in debug mode where before we may only check jvms() != NULL. I think you simply can add explicit check in macro.cpp code:
>>
>> !       // Not that preceding claim is documented anywhere else.
>> !       if (alock->jvms() != NULL && alock->is_Lock()) {
>> !         if (alock->as_Lock()->is_nested_lock_region()) {
>
> I didn't change jvms() assignment -- for Unlock nodes there is a debug-only second field to hold this information,
> because this is not the only place sensitive to which AbstractLock nodes have jvms() attached, and adding a jvms()
> to Unlock nodes caused additional failures.  So the original condition still works.

Okay, I got it.

Thanks,
Vladimir

>
> thanks for the review,
>
> David
>
>> Thanks,
>> Vladimir
>>
>> On 2/12/15 7:09 PM, David Chase wrote:
>>> http://cr.openjdk.java.net/~drchase/8069412/webrev.00/
>>>
>>> This is the debugging support that I found very helpful to make progress on
>>> https://bugs.openjdk.java.net/browse/JDK-8066576 "Lock still held"
>>>
>>> It comes in three parts:
>>>
>>> 1) When -XX:+Verbose, locks in stack backtrace are printed with additional information,
>>> like so:
>>>
>>> "FooThread" #19 daemon prio=10 os_prio=31 tid=0x00007fe41c2c8000 nid=0x6203 waiting for monitor entry [0x0000000110072000]
>>>     java.lang.Thread.State: BLOCKED (on object monitor)
>>>     JavaThread state: _thread_blocked
>>> Thread: 0x00007fe41c2c8000  [0x6203] State: _at_safepoint _has_called_back 0 _at_poll_safepoint 0
>>>     JavaThread state: _thread_blocked
>>>     at foo.Foo.send(Foo.java:21)
>>>     - waiting to lock <0x0000000780b89008> (a java.lang.Object)
>>>       lockbits= locked(0x00007fe41c23d09a)->monitor={count=0x0000000000000001,waiters=0x0000000000000000,recursions=0x0000000000000000,owner=0x00007fe41b8fc000}
>>>     at foo.Bar.bar(Bar.java:1)
>>>
>>> The new line is the one beginning "     lockbits".
>>> Without -XX:+Verbose, the old behavior remains.
>>>
>>> 2) In a debug (#ifdef ASSERT) build, when -XX+:LogCompilation is specified,
>>> additional records are written to the compilation log file describing which lock optimizations
>>> are performed (and in some cases, which are not performed, and why).
>>>
>>> For example:
>>>
>>>    <eliminate_lock_set_nested lock='0' compile_id='1840' class_id='unlock' kind='?' stamp='350.736'>
>>>    </eliminate_lock_set_nested>
>>>    <eliminate_lock_set_nested lock='1' compile_id='1840' class_id='lock' kind='coarsened' stamp='350.736'>
>>>    </eliminate_lock_set_nested>
>>>
>>> where the first record indicates that a previously unoptimized lock (kind='?') was set to 'nested'
>>> and the second record indicates that a previously coarsened lock was set to nested.
>>> Other additional information recorded includes locations for Unlock nodes.
>>>
>>> Even in release builds, the kind of elimination (nested, coarsened, non-escaping) is now noted.
>>>
>>> 3) The compilation processing tool was enhanced to process these new records, producing output like this:
>>>
>>> 1783 eliminate_lock_NOT_nested_lock_region ? lock  98.713 [@36 foo.Foo::fooMethod (330 bytes)]
>>> 1783 eliminate_lock_INLR_1 ? lock  98.713 [@36 foo.Foo::fooMethod (330 bytes)]
>>> 1783 eliminate_lock_set_nested ? unlock  98.713 [@-1 bar.BAR::setData (53 bytes), @54 foo.Foo::fooMethod (330 bytes)]
>>> 1783 eliminate_lock_set_nested ? lock  98.713 [@-1 bar.BAR::setData (53 bytes), @54 foo.Foo::fooMethod (330 bytes)]
>>> 1783 eliminate_lock_set_nested nested lock  98.713 [@-1 bar.BAR::setData (53 bytes), @54 foo.Foo::fooMethod (330 bytes)]
>>> 1783 eliminate_lock_set_nested ? unlock  98.713 [@-1 bar.BAR::getLength (5 bytes), @65 foo.Foo::fooMethod (330 bytes)]
>>> 1783 eliminate_lock_set_nested ? lock  98.713 [@-1 bar.BAR::getLength (5 bytes), @65 foo.Foo::fooMethod (330 bytes)]
>>> 1783 eliminate_lock_set_nested nested lock  98.713 [@-1 bar.BAR::getLength (5 bytes), @65 foo.Foo::fooMethod (330 bytes)]
>>> 1783 eliminate_lock_NOT_nested_lock_region ? lock  98.713 [@202 foo.Foo::fooMethod (330 bytes)]
>>> 1783 eliminate_lock_INLR_1 ? lock  98.713 [@202 foo.Foo::fooMethod (330 bytes)]
>>> 1783 eliminate_lock nested unlock  98.713 [@-1 bar.BAR::getLength (5 bytes), @65 foo.Foo::fooMethod (330 bytes)]
>>> 1783 eliminate_lock nested lock  98.713 [@-1 bar.BAR::getLength (5 bytes), @65 foo.Foo::fooMethod (330 bytes)]
>>> 1783 eliminate_lock nested unlock  98.714 [@-1 bar.BAR::setData (53 bytes), @54 foo.Foo::fooMethod (330 bytes)]
>>> 1783 eliminate_lock nested lock  98.714 [@-1 bar.BAR::setData (53 bytes), @54 foo.Foo::fooMethod (330 bytes)]
>>>
>>> This was tested running jtreg on compiler and runtime,
>>> as well as many runs of the problematic application for 8066576,
>>> plus JPRT of the hotspot testsuite,
>>> plus built with XCode 4.6.3 and 6.1.1 on Mavericks and gcc 4.8.2 on Ubuntu 14.04.
>>>
>>> David
>>>
>>>
>