RFR(L): 8140485: Class load and creation clean up
Markus Gronlund
markus.gronlund at oracle.com
Tue Dec 8 10:35:38 UTC 2015
Harold, Coleen and Serguei,
Thanks for your help in reviewing so far.
I have created an updated changeset which I intend to push if you are ok with it, please see:
http://cr.openjdk.java.net/~mgronlun/8140485/unified/unified_review/webrev05/
Coleen,
I went back to the CheckIntrinsic piece, and true, it was lost in the merging - thanks for pointing this out.
I have refactored that piece into a static function.
In addition, I reworked the is_public() member function to become is_internal() instead.
I have removed the explicit usages of the class_loader oop - thanks again. Where needed this will be picked up from the ClassLoaderData.
I have attempted to pack the fields better for ClassFileParser - thanks.
Harold,
Thanks for your help in reviewing this!
About your comments:
1. In classLoader.cpp could you add comments explaining why no_verification is specified to the ClassFileStream constructor?
[MG] Although these streams are currently loaded by the primordial class loader (which is the reason I construct them passing no_verification) and a comment such as "// the primordial class loader loads classes from a trusted repository" would be useful - I have now reconsidered this:
I will now pass ClassFileStream::verify when constructing these streams as well - the verification setting will be recalculated (updated and set) after stream creation at least twice before reaching the verification code. For most of these streams, the recalculated verification setting done after construction will be no_verification. It might be prudent in light of security to construct the streams defaulting to verify. This is also the default parameter for the ClassFileStream - however, I am passing them to be explicit.
2. Could you replace "invariant" with a more interesting message where appropriate in some of the asserts?
[MG] I agree that this would probably be helpful, but after I started an attempt in doing this, I realized that it would take quite some time to come up with some descriptive messages - maybe it would be ok to take this after integration?
3. In reflection.cpp, could you replace the switch statement in
get_mirror_from_signature() with an if/else statement?
[MG] Done!
Runtime/ParallelClassLoading tests completed.
JPRT checkin dry-run completed.
Thanks for your help
/Markus
-----Original Message-----
From: harold seigel
Sent: den 1 december 2015 22:49
To: hotspot-runtime-dev at openjdk.java.net
Subject: Re: RFR(L): 8140485: Class load and creation clean up
Hi Markus,
The restructuring looks good!
I just have a few minor comments.
1. In classLoader.cpp could you add comments explaining why no_verification is specified to the ClassFileStream constructor?
2. Could you replace "invariant" with a more interesting message where appropriate in some of the asserts?
3. In reflection.cpp, could you replace the switch statement in
get_mirror_from_signature() with an if/else statement?
Thanks! Harold
On 11/20/2015 1:27 PM, Markus Gronlund wrote:
> Hi Coleen,
>
> Many, many thanks for taking on this large change.
>
> Thanks for the feedback, I have updated like this:
>
> ClassFactory::create(...) -> KlassFactory::create_from_stream(...)
>
> // "Klass" better signifies internal representation (metadata) compared to "Class" which has a more classfile contextual association. Fixed.
> // In addition, I have removed all overloaded create_from_stream()
> functions, reducing them to a single create_from_stream(). The caller will // have to pass NULL on unused parameters with this tradeoff.
>
> // renaming
> ClassFileParser::instance_klass(...) ->
> ClassFileParser::create_instance_klass(...)
>
> ClassFileParser::fill_instance(...) ->
> ClassFileParser::fill_instance_klass(...)
>
> // moved the parse_stream() and post_process_stream() into the ClassFileParser constructor (process() removed) - thanks!
>
> Here is an updated webrev:
>
> http://cr.openjdk.java.net/~mgronlun/8140485/unified/unified_review/we
> brev03/
>
> Many thanks again
> Markus
>
>
> -----Original Message-----
> From: Coleen Phillimore
> Sent: den 20 november 2015 04:51
> To: hotspot-runtime-dev at openjdk.java.net
> Subject: Re: RFR(L): 8140485: Class load and creation clean up
>
>
> Hi, More comments on classFileParser.
>
> It seems like the ClassFileParser::process is unnecessary as a
> function. I think the 3 lines should be imported into
> ClassFileParser::ClassFileParser and it makes sense there.
>
>> Summary:
>>
>> Reduce the visibility of CFP impl methods by internal linkage instead of external linkage.
>>
>> Comment:
>>
>> In my opinion, we should attempt to break the pattern of having private functions declared in header files when the private function does not need to reach inside "this".
> Yes, I agree and appreciate moving all of these functions static and internal in CFP.
>
> Coleen
>
>
> On 11/12/15 7:08 AM, Markus Gronlund wrote:
>> Hi again,
>>
>> I have reworked and simplified this clean up/refactoring suggestion:
>>
>> Updated high-level description:
>> http://cr.openjdk.java.net/~mgronlun/8140485/unified/unified_review/8
>> 1
>> 40485_updated.jpg
>>
>> Updated webrev:
>> http://cr.openjdk.java.net/~mgronlun/8140485/unified/unified_review/w
>> e
>> brev02/
>>
>> Updated patch:
>> http://cr.openjdk.java.net/~mgronlun/8140485/unified/unified_review/8
>> 1
>> 40485_open_unified_updated.patch
>>
>> Thanks in advance
>> Markus
>>
>>
>> -----Original Message-----
>> From: Markus Gronlund
>> Sent: den 27 oktober 2015 13:21
>> To: hotspot-runtime-dev at openjdk.java.net;
>> serviceability-dev at openjdk.net
>> Subject: RFR(L): 8140485: Class load and creation clean up
>>
>> Greetings,
>>
>>
>>
>> I have spent some time refactoring and cleaning up parts of the class load and creation sequence and code.
>>
>>
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8140485
>>
>> Overview:
>>
>> There are quite a lot of changes here - hopefully it will not be a deterrent of taking this on- first of all, a lot of changes are mechanical and applicable to "form" more than content- for example, variable, parameter and member function "constness". Same applies to other "domino changes", for example when moving an included header from a .hpp file (maybe replacing with a fwd decl instead).
>>
>>
>>
>> I have tried to stage the changes for easier overview / review (including a high level diagram). The patches/webrevs are split into a patch series of 7 patches (there is also a unified patch).
>>
>>
>>
>> Use case:
>>
>> My initial use case for starting all of this clean up / refactoring work is a need to reuse mechanics of the class parsing and creation sequence.
>>
>>
>>
>> Cleanup / refactoring objectives:
>>
>>
>>
>> - Allow for class parsing implementation reuse
>>
>> - Decouple class parsing and Klass creation
>>
>> - Decouple JVMTI class file load hook from ClassFileParser
>>
>> - Add compiler assisted read-only intent in order to assist future refactoring attempts
>>
>> - "componentify" ClassFileParser / apply to Klass/IK/AK creations
>>
>> - Take advantage of some optimizations opportunities (constructors and underlying "calloc" memory)
>>
>> - Maintain class load performance
>>
>>
>>
>> High level diagram explaining the updated suggested sequence (high level):
>>
>> http://cr.openjdk.java.net/~mgronlun/8140485/8140485_Class_load_and_c
>> r eation_cleanup_high_level_sequence.jpg
>>
>>
>>
>> Split webrevs/patches for easier overview / review (do note that not all of these splits will compile individually - there is a unified patch link that includes everything, pls see below):
>>
>>
>>
>> Sequence: "first" (order of changes)
>>
>> Name: "8140485_1_unified entry point"
>>
>> Link:
>> http://cr.openjdk.java.net/~mgronlun/8140485/split/first/webrev01/
>>
>> Summary:
>>
>> Split out JVMTI agent CFLH from CFP - moved to SD::create_vm_representation_prologue().
>>
>> Channel all class loading via a unified entry point -
>> SD::create_vm_representation()
>>
>> Split out ClassPathEntry into own header.
>>
>> Creation of new class ClassPathFileStream (specialized ClassPathStream) to retain ClassLoaderExt::Context functionality in the refactored code.
>>
>> "Need verify" property is carried within the CFS itself.
>>
>> Comment:
>>
>> SystemDictionary::load_instance_class() will now have a call to
>> "load_class_from_classpath" - the relevance of this name might need
>> to be modified (modules etc?)
>>
>>
>>
>> Sequence: "second"
>>
>> Name: "8140485_2_read_only_class_file_stream"
>>
>> Link:
>> http://cr.openjdk.java.net/~mgronlun/8140485/split/second/webrev01/
>>
>> Summary:
>>
>> The underlying bytestream (buffer) in a CFS representation should not be altered (advertently or inadvertently) once created, made read-only.
>>
>> Comment:
>>
>> Modifications should work with copies.
>>
>>
>>
>> Sequence: "third"
>>
>> Name: "8140485_3_componentify_class_file_parser"
>>
>> Link:
>> http://cr.openjdk.java.net/~mgronlun/8140485/split/third/webrev01/
>>
>> Summary:
>>
>> In order to allow for code refactoring of CFP - stack allocated variables are modified into fields. The entire CFP acts as a generic RAII class for the allocated structures (note CHECK macros).
>>
>> I have not fulfilled refactoring of some of the longest methods since it's is hard to really understand the impact of the inlining I guess we are after here..
>>
>> The performance work done so far indicated improvements in still passing parameters instead of reading the fields directly (so you might still see "fat" methods taking a lot of parameters even though the fields are set).
>>
>>
>> "Consts everywhere.."
>>
>> One of the real hard issues trying to refactor this code is the lack of expressed read-only intent - it's hard to determine (both on reading but more importantly when compiling) what can/should change.
>>
>> Yes, I have entered the "const" rabbit hole related to this code (in some cases it might even be termed gratuitous (event 'consting' function parameter pointers in some cases for example)) - hopefully this will help in upcoming attempts to refactor/simplify this code.
>>
>>
>>
>> Accessors - CFP becomes a data container to be used in constructors
>> (see change seven). In addition, you will now have a possibility to
>> fetch data from a parser without creating a fullblown Klass
>>
>>
>>
>> Comment:
>>
>> I think the code could be improved and more refactoring could be
>> accomplished by introducing a Metaspace allocation RAII class - this
>> would allow the functions to decouple even more that is currently
>> (might be next steps)
>>
>>
>>
>> Sequence: "fourth"
>>
>> Name: "8140485_4_hide_impl_details_class_file_parser"
>>
>> Link:
>> http://cr.openjdk.java.net/~mgronlun/8140485/split/fourth/webrev01/
>>
>> Summary:
>>
>> Reduce the visibility of CFP impl methods by internal linkage instead of external linkage.
>>
>> Comment:
>>
>> In my opinion, we should attempt to break the pattern of having private functions declared in header files when the private function does not need to reach inside "this".
>>
>> (that is, it can use an external interface alt. might not need access
>> at all (helpers))
>>
>>
>>
>> Sequence: "fifth"
>>
>> Name: "8140485_5_update_entry_point"
>>
>> Link:
>> http://cr.openjdk.java.net/~mgronlun/8140485/split/fifth/webrev01/
>>
>> Summary:
>>
>> Update signatures. Remove the parameter passing where not needed
>> ("parsed_name" reference for example)
>>
>>
>>
>> Sequence: "sixth"
>>
>> Name: "8140485_6_types_const_includes_repercussions"
>>
>> Link:
>> http://cr.openjdk.java.net/~mgronlun/8140485/split/sixth/webrev01/
>>
>> Summary:
>>
>> Rippling effects of stronger constness.
>>
>> Forward includes where can be applied. This revealed other code modules not having includes -added.
>>
>> Downcasting of const qualified types (applied Scott Meyers idiom of
>> dual const_cast additions (see Effective C++))
>>
>>
>>
>> Sequence: "seventh"
>>
>> Name: "8140485_7_applied_use_in_constructors_and_some_optimizations"
>>
>> Link:
>> http://cr.openjdk.java.net/~mgronlun/8140485/split/seventh/webrev01/
>>
>> Summary:
>>
>> Take advantage of above modifications to gain direct upshots in other areas. Use CFP as the data container when constructing Klass/IK/AK.
>>
>> Optimizations: Reduce/optimize Klass/InstanceKlass/ArrayKlass/ConstantPool constructors by using underlying invariant on "calloc" equivalent MetaspaceObj allocations.
>>
>>
>>
>> Unified change/patch:
>>
>> Webrev:
>> http://cr.openjdk.java.net/~mgronlun/8140485/unified/webrev01/
>>
>> Patch:
>> http://cr.openjdk.java.net/~mgronlun/8140485/unified/8140485_unified.
>> p
>> atch
>>
>> Summary:
>>
>> Unified (folded) patch for easier application/imports, for
>> compilation/try out
>>
>>
>>
>> Testing:
>>
>> I have done targeted testing during development especially using the
>> "runtime/ParallelClassLoading" test suite in order to ensure
>> functional equivalency. JPRT testing. Performance tests (see below)
>>
>>
>>
>> Performance:
>>
>> Unstructured:
>>
>> I have used Java Flight Recorder (JFR), which envelops the class loading sequence with high resolution timers - I have used this information to ensure performance has been stable regarding the changes.
>>
>>
>>
>> Structured:
>>
>> Startup/footprint-benchmarks (Linux32, Linux64, Windows32, Windows64,
>> Solaris SPARC-T)
>>
>>
>>
>> It is hard to read anything decisive around these (the effects most
>> likely hides in noise), but at least determine that the changes do
>> not introduce anything statistically significant (+/-) (both time and
>> space)
>>
>> Thanks in advance
>>
>> Markus
>>
>>
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