RFR(L): 8146401: Clean up oop.hpp: add inline directives and fix header files

[Volker Simonis]

On Fri, Jan 8, 2016 at 8:53 AM, David Holmes <david.holmes at oracle.com> wrote:
>
>
> On 8/01/2016 5:28 PM, Lindenmaier, Goetz wrote:
>>
>>
>>
>>> -----Original Message-----
>>> From: David Holmes [mailto:david.holmes at oracle.com]
>>> Sent: Freitag, 8. Januar 2016 06:07
>>> To: Lindenmaier, Goetz <goetz.lindenmaier at sap.com>; hotspot-runtime-
>>> dev at openjdk.java.net
>>> Subject: Re: RFR(L): 8146401: Clean up oop.hpp: add inline directives and
>>> fix
>>> header files
>>>
>>> On 8/01/2016 1:01 AM, Lindenmaier, Goetz wrote:
>>>>
>>>> Hi David,
>>>>
>>>> the documentation you point to makes the point that whether to inline
>>>> is an implementation detail, and that that should not be annotated to
>>>> the declaration.  Basically, this is a good point.
>>>>
>>>> But the documentation does not cover the fact that
>>>> we have the implementation in a different file than the declaration.
>>>> The .inline.hpp is not included always (as you pointed out).
>>>>
>>>> Therefore, if we compile with precompiled headers, we get more
>>>> inlines than if we do so without.
>>>> Further, many functions were moved to oop.linline.hpp during the
>>>> recent cleanups, and I think all the #includes I had to add were not
>>>> left out deliberately, but just happened because the compiler did
>>>> not complain.
>>>> I think if somebody decides not to place a function implementation
>>>> in a .cpp file, it should have the chance to be inlined at all it's
>>>> calls.
>>>> Putting the 'inline' into the .hpp file assures this.
>>>
>>>
>>> Sorry I don't follow that. If you include the .inline.hpp you don't need
>>> "inline" in the .hpp. If you don't include it then the compiler doesn't
>>> have access to the definition so that it can be inlined.
>>
>> Yes.
>>
>>> it seems to me that if
>>> you want it inlined then you must include the .inline.hpp anywhere it is
>>> needed. Anything else seems a bad-aid.
>>
>> But I think not the caller should decide whether it's to be inlined,
>> but the implementor of the method (and next the compiler).
>> As you describe, the caller has to decide which header to include.
>> So the caller has to know implementation details of the callee,
>> which is contrary to the encapsulation described in that documentation.
>
>
> That's my understanding of the way things are expected to work. This is not
> a public library exporting its interface in a .hpp file, this an internal
> part of the bigger system. As I understand it we define the .inline.hpp file
> precisely so that clients can include it. And yes the clients have to know
> to do that.
>
>> If you add the 'inline' keyword in the header, the compiler enforces
>> that the includes are in a way that it can do what the implementor
>> of the callee / of the method to be inlined intended.
>
>
> I still don't see how adding inline to the declaration changes anything
> here. The compiler can't do the inlining unless the .inline.hpp file has
> been included. ???
>

If you put a method definition into an .inline.hpp file your intention
as programmer is that this method should always be inlined by the
compiler.

But if you declare it without the "inline" keyword in the .hpp file,
users may by mistake include the .hpp file instead of the .inline.hpp
file and call your function without it being inlined by the compiler.

The .hpp file should only be included by users who don't call any of
the inline functions from the classes defined in that .hpp file. If
they want to call some inline functions, they have to include the
.inline.hpp file. Goetz's change ensures exactly this. It prevents
users from mistakenly including a .hpp file but calling inline
functions from the corresponding .inline.hpp file. (As a side note: we
had compilers which produced linking errors in such situations because
the compiler didn't create instances for the inline functions from the
.inline.hpp file).

Regards,
Volker


> Cheers,
> David
> -----
>
>
>
>>> Maybe
>>> precompiled headers messes with that somehow
>>
>> Actually, you are right.  Oop.inline.hpp is not in precompiled.hpp, nor
>> is it dragged in by some other .inline.hpp header.
>> I would assume this is a remnant of the problems with this header.
>> But if it was listed there, it would make a difference.
>>
>> To put it the other way round: do you think all the places I had to
>> clean up are well founded decisions not to include the methods
>> from oop.inline.hpp?
>> Before my change, the caller of obj_at_put() from objArrayOop.hpp
>> had to include oop.inline.hpp to get it properly inlined.  Seems very
>> unintuitive to me.
>>
>> http://cr.openjdk.java.net/~goetz/wr16/8146401-oopInline-rt/webrev.01/src/share/vm/oops/objArrayOop.hpp.udiff.html
>> (I'll add the inline keyword in a follow-up change for gc files, in case
>> this change is accepted.)
>>
>> Best regards,
>>    Goetz.
>>
>>>
>>> Cheers,
>>> David
>>>
>>>> Best regards,
>>>>     Goetz.
>>>>
>>>>
>>>>
>>>>
>>>>> -----Original Message-----
>>>>> From: David Holmes [mailto:david.holmes at oracle.com]
>>>>> Sent: Mittwoch, 6. Januar 2016 05:59
>>>>> To: Lindenmaier, Goetz <goetz.lindenmaier at sap.com>; hotspot-runtime-
>>>>> dev at openjdk.java.net
>>>>> Subject: Re: RFR(L): 8146401: Clean up oop.hpp: add inline directives
>>>>> and
>>>
>>> fix
>>>>>
>>>>> header files
>>>>>
>>>>> Hi Goetz,
>>>>>
>>>>> On 5/01/2016 1:44 AM, Lindenmaier, Goetz wrote:
>>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> Several recent changes cleaned up includes of oop.inline.hpp in real
>>>>>> .hpp
>>>>>
>>>>> header file.
>>>>>>
>>>>>> Unfortunately, the 'inline' qualifier is added to the function
>>>>>
>>>>> implementations
>>>>>>
>>>>>> in oop.inline.hpp instead of to the declarations in oop.hpp.
>>>>>> Therefore,
>>>
>>> the
>>>>>>
>>>>>> compiler can not detect failing inlines properly.
>>>>>>
>>>>>> This change moves the inline directive from oop.inline.hpp to oop.hpp.
>>>>>
>>>>> Also
>>>>>
>>>>> This seems contrary to the C++ FAQ:
>>>>>
>>>>> https://isocpp.org/wiki/faq/inline-functions
>>>>>
>>>>> The declaration in the .hpp should not have inline, only the
>>>>> definition,
>>>>> which in our case is in the .inline.hpp file.
>>>>>
>>>>> Any code that includes the .inline.hpp will have seen the definition of
>>>>> the inline function prior to its use - as long as the includes are
>>>>> correct.
>>>>>
>>>>> David
>>>>> -----
>>>>>
>>>>>
>>>>>> it sorts the methods in oop.inline.hpp as they are sorted in oop.hpp.
>>>>>>
>>>>>> Further, it moves a row of calls from hpp files to inline.hpp or .cpp
>>>>>> files.
>>>>>>
>>>>>> I put oop.inline.hpp into serviceUtil.hpp.  This is not clean, but
>>>>>> this is a
>>>>>> very small .hpp file and no .cpp file exists.  So I think this is
>>>>>> acceptable.
>>>>>>
>>>>>> Also, I put oop.inline.hpp into jvmciJavaClasses.hpp.  I don't want to
>>>>>> do
>>>>>> bigger changes to this file in the rt repo, because jvmci is subject
>>>>>> to
>>>>>> freqent changes recently.
>>>>>>
>>>>>> The following methods were moved to .cpp files:
>>>>>>
>>>>>> ProtectionDomainCacheTable::compute_hash()
>>>>>> ProtectionDomainCacheTable::index_for()
>>>>>> typeArrayOopDesc::object_size()
>>>>>> This is called only once outside .cpp file:
>>>>>> CallSiteDepChange::CallSiteDepChange()
>>>>>> This is only called in .cpp file
>>>>>> ConstantPool::string_at_put()
>>>>>>
>>>>>> If someone considers not inlining these harmful to performance,
>>>>>> I will add a new .inline.hpp file for them.
>>>>>>
>>>>>> Please review this change.  I please need a sponsor.
>>>>>> There are no functional edits, so it should be simple to review.
>>>>>> http://cr.openjdk.java.net/~goetz/wr16/8146401-oopInline-
>>>
>>> rt/webrev.01/
>>>>>>
>>>>>>
>>>>>> Best regards,
>>>>>>      Goetz.
>>>>>>
>