RFR: 8247536: Support for pre-generated java.lang.invoke classes in CDS static archive

[Yumin Qi]

Hi, Mandy


On 8/20/20 5:10 PM, Mandy Chung wrote:
>
>
> On 8/19/20 10:14 PM, Yumin Qi wrote:
>>
>> HI, Mandy
>>
>>   Thanks for the review, I took one day off yesterday so just got a detail look of your reply.
>>
>> On 8/19/20 1:30 PM, Mandy Chung wrote:
>>> On 8/17/20 12:37 PM, Yumin Qi wrote:
>>>> Hi, Ioi
>>>>
>>>>   Thanks for review/suggestion. I have updated the webrev at the following link:
>>>>
>>>> http://cr.openjdk.java.net/~minqi/2020/8247536/webrev-02/
>>>>
>>>
>>> This patch leverages the TRACE_RESOLVE output and passes the trace output to VM.  VM then calls GenerateJLIClassesHelper::generateMHHolderClasses to do the parsing and generate Holder class per the resolved LFs.   I think there are other cleaner alternatives implementing this.   jlink --generate-jli-classes plugin depends the trace output whereas -Xshare:dump does not.   It's cleaner to skip generating the trace output and parsing for dumping shared archive purpose.  In addition, the implementation needs some cleanup (I can send you feedback on the next revision)
>>>
>> Current patch did not change the existing code for JLinkPlugin part. I just moved the parsing code from GenerateJLIClassesPlugin.java to GenerateJLIClassesHelper.java since the former is an internal class to which we shouldn't call to generate holder classes.
>>> Instead of relying on a system property "java.lang.invoke.MethodHandle.CDS_TRACE_RESOLVE", it's better to use jdk.internal.vm.isCDSDumpingEnabled() to detect if this is CDS dump time.
>>
>> I remember we have such API to query if flag -Xshare:dump or -Xshare:on used. Do you mean if DumpLoadedClassList flag set? This flag is the one used to log class name to list file. In GenerateLinkOptData.gmk:
>>
>> $(CLASSLIST_FILE): $(INTERIM_IMAGE_DIR)/bin/java$(EXE_SUFFIX) $(CLASSLIST_JAR)
>>         $(call MakeDir, $(LINK_OPT_DIR))
>>         $(call LogInfo, Generating $(patsubst $(OUTPUTDIR)/%, %, $@))
>>         $(call LogInfo, Generating $(patsubst $(OUTPUTDIR)/%, %, $(JLI_TRACE_FILE)))
>>         $(FIXPATH) $(INTERIM_IMAGE_DIR)/bin/java -XX:DumpLoadedClassList=$@.raw \
>>             -Duser.language=en -Duser.country=US \
>>             -cp $(SUPPORT_OUTPUTDIR)/classlist.jar \
>>             build.tools.classlist.HelloClasslist $(LOG_DEBUG)
>>         $(GREP) -v HelloClasslist $@.raw > $@.interim
>>         $(FIXPATH) $(INTERIM_IMAGE_DIR)/bin/java -Xshare:dump \
>>             -XX:SharedClassListFile=$@.interim -XX:SharedArchiveFile=$@.jsa \
>>             -Xmx128M -Xms128M $(LOG_INFO)
>>         $(FIXPATH) $(INTERIM_IMAGE_DIR)/bin/java -XX:DumpLoadedClassList=$@.raw.2 \
>>             -XX:SharedClassListFile=$@.interim -XX:SharedArchiveFile=$@.jsa \
>>             -Djava.lang.invoke.MethodHandle.TRACE_RESOLVE=true \
>>             -Duser.language=en -Duser.country=US \
>>             --module-path $(SUPPORT_OUTPUTDIR)/classlist.jar \
>>             -cp $(SUPPORT_OUTPUTDIR)/classlist.jar \
>>             build.tools.classlist.HelloClasslist \
>>             2> $(LINK_OPT_DIR)/stderr > $(JLI_TRACE_FILE) \
>>             || ( \
>>                 exitcode=$$? ; \
>>                 $(ECHO) "ERROR: Failed to generate link optimization data." \
>>                     "This is likely a problem with the newly built JVM/JDK." ; \
>>                 $(CAT) $(LINK_OPT_DIR)/stderr $(JLI_TRACE_FILE) ; \
>>                 exit $$exitcode \
>>             )
>>         $(GREP) -v HelloClasslist $@.raw.2 > $@
>>
>> The $(JLI_TRACE_FILE) is generated with both -XX:DumpLoadedClassList and -Djava.lang.invoke.MethodHandle.TRACE_RESOLVE=true, in current implementation, DumpLoadedClassList will turn on property java.lang.invoke.MethodHandle.CDS_TRACE_RESOLVE=true. So the same output sent to stdout and log file DumpLoadedClassList specified.
>>
>
> These entries are duplicated in two different files: one for jlink --generate-jli-classes plugin and another for CDS use.  CDS -Xshare:dump attempts to do what jlink plugin does but writes those generated classes in to shared archive.
>
> Like the above make logic to build JDK image, the same entries are written in both default-jli-trace.txt via System.out and to classlist via JNI call to the VM.  I guess VM also implements the logic to do some kind of diffing and write to CDS archive.
>
In current implementation, vm side only records the line as from TRACE_RESOLVE at pre-run with -XX:DumpLoadedClassList, and at dump time, call back to java for parsing those recordings and generating the holder classes, this uses the existing JLI code.
>>
>> Now instead of this property, using a vm interface API to query if this flag is set, I think it is better choice. But here I am NOT sure I understand your suggestion, I think there are two choices:
>>
>> 1) Using DumpLoadedClassList to collect TRACE_RESOLVE but not via CDS_TRACE_RESOLVE, using new API to query if DumpLoadedClassList is set
>>
>> 2) Do not use DumpLoadedClassList, when -Xshare:dump collecting those name, type and holder name to regenerate holder classes?
>>
>
> I misunderstood that this CDS_TRACE_RESOLVE flag is set during -Xshare:dump time.
>
> Ioi has clarified to me offline that this step is actually part of -XX:DumpLoadedClassList and includes these TRACE_RESOLVE logs to the given class list file, i.e. you repurpose the class list file to include the log output that was initially designed for jlink plugin.
>
> To me, I'd prefer to see this support depending on `jlink --generate-jli-classes` which is an existing functionality and much cleaner.  This way this does not require any VM change.   It will generate the holder classes in the custom image per the application-specific config file.
>
> What it means is that: a customer would need to create a custom image with their application-specific config file.  It might need a new CDS  option to specify a separate TRACE_RESOLVE file.   It would turn on this feature by default by defining a default path of the log file if it helps.
>
So for now, I would implement an API to query if flag DumpLoadedClassList set in cmd line, remove new added property of java.lang.invoke.MethodHandle.CDS_TRACE_RESOLVE. We can address custom image with CDS in future in a separate issue.


Thanks

Yumin

> I understand that this is not the existing CDS work flow and CDS archive does not require to run on a custom image.   I see the value of this approach which can prepare customers to start building and using its own custom image.
>
> Of course the implementation would be much simpler (adding a flag to write these traces to a given file path, that is).
>
> Mandy