RFR (S) 8235765: Use of the long type should be avoided in shared code

Coleen Phillimore coleen.phillimore at oracle.com
Sat Aug 15 10:59:18 UTC 2020 


On 8/14/20 7:58 PM, David Holmes wrote:
> Hi Coleen,
>
> I suggest just leaving the elfFile stuff alone. AFAICS the underlying 
> offset is 32-bit on 32-bit and 64-bit on 64-bit and on the platforms 
> we use ElfFile the use of "long" matches that (ILP32 and LP64). This 
> code should probably be using some of the Elf types directly, hidden 
> by a typedef to hide the 32-bit versus 64-bit nomenclature.

Ok, I reverted elfFile.* also.

open webrev at http://cr.openjdk.java.net/~coleenp/2020/8235765.03/webrev

Thanks!
Coleen
>
> David
>
> On 15/08/2020 9:19 am, David Holmes wrote:
>> On 13/08/2020 10:20 pm, Coleen Phillimore wrote:
>>> On 8/13/20 12:07 AM, David Holmes wrote:
>>>> Hi Coleen,
>>>>
>>>> And it seemed so simple when you started :)
>>>
>>> Oh gosh no, this sort of change is never simple!
>>>>
>>>> On 13/08/2020 6:43 am, Coleen Phillimore wrote:
>>>>>
>>>>> Hi Vladimir,  Thank you for looking at this change.
>>>>>
>>>>> On 8/12/20 1:25 PM, Vladimir Kozlov wrote:
>>>>>> Hi Coleen,
>>>>>>
>>>>>> I think it is safe to use 'uint' (uint32_t) for all counts in 
>>>>>> sweeper.
>>>>
>>>> "long" is only 32-bit on 64-bit Windows, so if we don't see any 
>>>> issues on Windows then there is a case to be made that all these 
>>>> long fields would appear to be fine if only 32-bit ... that said 
>>>> some of them "obviously" look like they should be size_t as you 
>>>> have made them.
>>>>
>>>>>> What is a story about using int64_t vs jlong? And others *_t vs 
>>>>>> j* types.
>>>>>
>>>>> jlong is a signed type (either long or long long) so in mutex, 
>>>>> even > though uint64_t makes more sense, I used int64_t so that 
>>>>> they'd be
>>>>> convertible to jlong in the PlatformMutex layer.  I didn't want to 
>>>>> pull the string of this sweater even further to convert the jlong 
>>>>> to uint64_t in that layer. (If that's even the right thing to 
>>>>> do).  We have been trying to avoid using java types like jint, 
>>>>> jlong etc, in shared code, but they're pretty much everywhere.
>>>>
>>>> We've been avoiding unnecessary use of j* types in the VM (shared 
>>>> or not) but when the values represent values to/from Java code then 
>>>> the j* types are appropriate. The multiple abstractions 
>>>> Parker/ParkEvent/PlatformEvent/PlatformParker/PlatformMonitor/Monitor 
>>>> make it hard to see exactly how values flow through, and which ones 
>>>> come direct from Java. We should keep the jlong at the 
>>>> Java-connected api level and use uint64_t elsewhere. Separate RFE 
>>>> of course. :)
>>>
>>> Yes, another sort of hard-to-impossible to completely fix RFE.  I 
>>> really think we should just fix individual occurrences as they're 
>>> found and discourage new uses.  Ideally we should translate all j* 
>>> types to their appropriate int types once they get passed into the 
>>> VM implementation code.
>>>>
>>>>
>>>> Looking at webrev v02:
>>>>
>>>> src/hotspot/share/memory/filemap.hpp
>>>>
>>>> You changed the field from long to int64_t but you didn't change 
>>>> the accessor:
>>>>
>>>> 87   long   filesize()  const { return _filesize; }
>>>
>>> Rats missed one.  I wish the compiler would have complained about 
>>> this. Nothing calls this function so I removed it (_filesize is used 
>>> directly).
>>
>> Ok.
>>
>>>>
>>>> that could give a truncation warning on Windows. That field is set 
>>>> from the stat st_size field, which is defined as type off_t on 
>>>> non-Windows and as ... okay I can't make sense of the win32 docs to 
>>>> figure out whether a plain stat will be a 64-bit or 32-bit [1]. So 
>>>> not clear what the right type is here - but the field and accessor 
>>>> should match.
>>>>
>>>> [1] 
>>>> https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/stat-functions?view=vs-2019 
>>>>
>>>>
>>>> ---
>>>>
>>>> src/hotspot/share/utilities/elfFile.cpp
>>>>
>>>> fseek is specified to take a long for the offset, so this change 
>>>> would be a problem on 32-bit builds I think.
>>>
>>> These files aren't compiled on windows.  I compiled this on arm32. I 
>>> think there "long" is 64 bits.
>>
>> No "long" is 32-bit on all 32-bit platforms. So I would expect 
>> passing a 64-bit value to a library function expecting a 32-bit 
>> argument should generate a compiler warning at best. The fact it 
>> doesn't is a concern. I'd be worried about the correctness of this 
>> code now.
>>
>> David
>>
>>
>>> #if !defined(_WINDOWS) && !defined(__APPLE__)
>>>
>>> Thanks,
>>> Coleen
>>>
>>>>
>>>> Thanks,
>>>> David
>>>> -----
>>>>
>>>>
>>>>
>>>>>>
>>>>>> Also you need to look on JFR code which collect these data:
>>>>>>
>>>>>> src/hotspot//share/jfr/periodic/jfrPeriodic.cpp: 
>>>>>> event.set_methodReclaimedCount(NMethodSweeper::total_nof_methods_reclaimed()); 
>>>>>>
>>>>>>
>>>>>> src/hotspot//share/jfr/metadata/metadata.xml: <Field type="int" 
>>>>>> name="methodReclaimedCount" label="Methods Reclaimed" />
>>>>>>
>>>>>> And I found that metadata.xml have several 'long' uses too:
>>>>>>
>>>>>> src/hotspot//share/jfr/metadata/metadata.xml: <Field type="long" 
>>>>>> contentType="millis" name="peakTimeSpent" label="Peak Time" />
>>>>>>
>>>>>> Looking on codecache code and sweeper and I see a lot of 
>>>>>> inconsistencies in used types :(
>>>>>> May be we need an other (compiler) RFE to clean that up.
>>>>>
>>>>> Yes, I agree. I'm going to revert sweeper, nmethod and vmStructs. 
>>>>> It's better that 'long' is fixed individually in the sweeper and 
>>>>> associated files.
>>>>>
>>>>> The JFR metadata.xml has a lot of "long" types declared in it. I'm 
>>>>> going to revert compileBroker.* too.   This is going to have to be 
>>>>> fixed a little at a time.
>>>>>
>>>>> I'm testing a new more limited version of this change now.
>>>>>
>>>>> Thanks,
>>>>> Coleen
>>>>>>
>>>>>> Regards,
>>>>>> Vladimir K
>>>>>>
>>>>>> On 8/12/20 10:00 AM, Coleen Phillimore wrote:
>>>>>>>
>>>>>>>
>>>>>>> On 8/12/20 12:19 PM, Lois Foltan wrote:
>>>>>>>> On 8/12/2020 11:21 AM, Coleen Phillimore wrote:
>>>>>>>>> Summary: Changed some long declarations to uint64_t/int64_t or 
>>>>>>>>> unsigned int, depending on context.
>>>>>>>>>
>>>>>>>>> There are still 'long' declarations left in the code, but they 
>>>>>>>>> should be changed by developers when working in that code and 
>>>>>>>>> not as a blanket change.  I didn't change a couple of longs in 
>>>>>>>>> jfr/leakprofiler, for example. These are the ones I changed 
>>>>>>>>> though with some explanation of why:
>>>>>>>>>
>>>>>>>>> src/hotspot/share/memory/filemap.hpp
>>>>>>>>>
>>>>>>>>> This can be negative so changed to int64_t.
>>>>>>>>>
>>>>>>>>> src/hotspot/share/runtime/mutex.cpp
>>>>>>>>>
>>>>>>>>> The PlatformMutex code takes jlong, which is signed, so that's 
>>>>>>>>> why I changed these to int64_t.
>>>>>>>>>
>>>>>>>>> runtime/interfaceSupport.inline.hpp
>>>>>>>>>
>>>>>>>>> These counters are actually intervals so I changed them to 
>>>>>>>>> unsigned int.
>>>>>>>>>
>>>>>>>>> src/hotspot/share/compiler/compileBroker.hpp
>>>>>>>>>
>>>>>>>>> _peak_compilation_time is signed because it is compared with 
>>>>>>>>> jlong which is signed.
>>>>>>>>> Same with total_compilation_time - elapsedTimer.milliseconds() 
>>>>>>>>> returns jlong.
>>>>>>>>>
>>>>>>>>> Tested with tier1-3.  Tier1 on linux-x64-debug, 
>>>>>>>>> windows-x64-debug, macosx-x64-debug, linux-aarch64-debug. Also 
>>>>>>>>> built on: 
>>>>>>>>> linux-arm32,linux-ppc64le-debug,linux-s390x-debug,linux-x64-zero.
>>>>>>>>>
>>>>>>>>> open webrev at 
>>>>>>>>> http://cr.openjdk.java.net/~coleenp/2020/8235765.01/webrev
>>>>>>>>> bug link https://bugs.openjdk.java.net/browse/JDK-8235765
>>>>>>>>>
>>>>>>>>> Thanks,
>>>>>>>>> Coleen
>>>>>>>>
>>>>>>>> Hi Coleen,
>>>>>>>>
>>>>>>>> Looks good.
>>>>>>>>
>>>>>>>> - runtime/sweeper.hpp
>>>>>>>>   This is the only file that I wondered why you changed long to 
>>>>>>>> int64_t for _total_nof_methods_reclaimed and 
>>>>>>>> _total_nof_c2_methods_reclaimed.  Note that the method 
>>>>>>>> NMethodSweeper::total_nof_methods_reclaimed returns an int. 
>>>>>>>> Could both of these fields be changed to int instead?
>>>>>>>
>>>>>>> Hi Lois, Thank you for looking at this. Unfortunately, this was 
>>>>>>> an outdated webrev, can you hit reload?  I changed these fields 
>>>>>>> to be uint64_t because they're never signed.  It's likely that 
>>>>>>> the number of methods is never greater than an int, but since it 
>>>>>>> was long to begin with, I kept 64 bit until someone decides an 
>>>>>>> 'int' is better. Since number_of_codecache_sweeps is uint64_t, 
>>>>>>> which seems like a lot too, there could be that many nmethods 
>>>>>>> reclaimed.  I retested with windows just now to be sure.
>>>>>>>
>>>>>>> Thanks,
>>>>>>> Coleen
>>>>>>>
>>>>>>>
>>>>>>>>
>>>>>>>> Thanks,
>>>>>>>> Lois
>>>>>>>
>>>>>
>>>

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