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

[David Holmes]

Hi David,

On 17/02/2015 4:09 AM, David Chase wrote:
> Improved webrev, should address issues:
>
> http://cr.openjdk.java.net/~drchase/8069412/webrev.03/
>
> I did some more work on LogCompilation -- testing (there is none for that tool in jtreg or JPRT)
> revealed that the 9+changes tool would crash on 8u logs, and that (1) made it hard for me to test
> my changes against existing logs known to contain new-features data and (2) seems kinda graceless
> anyhow.

Runtime aspects seem okay to me (rest seems okay too but I'm not a 
compiler guy :)).

Minor style nit in basicLock.cpp:

   +     moop -> print_on(st);

No spaces around ->

Thanks,
David H.

> David
>
> On 2015-02-13, at 11:50 AM, Vladimir Kozlov <vladimir.kozlov at oracle.com> wrote:
>
>> 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
>>>>>
>>>>>
>>>
>