8264124: Update MXBean specification and implementation to extend mapping of CompositeType to records #3201

dfuch · 2021-03-25T17:30:52Z

This RFE proposes to extend the MXBean framework to define a mapping to records.

The MXBean framework already defines a mapping of CompositeType to plain java objects. Records are a natural representation of CompositeTypes. A record can be easily reconstructed from a CompositeData through the record canonical constructor. A clear advantage of records over plain java objects is that the canonical constructor will not need to be annotated in order to map composite data property names to constructor parameter names.

With this RFE, here is an example comparing coding a composite type NamedNumber that consists of an int and a String, using records and using a plain java class. In both case, the CompositeType looks like this:

CompositeType(
    "NamedNumber",                      // typeName
    "NamedNumber",                      // description
    new String[] {"number", "name"},    // itemNames
    new String[] {"number", "name"},    // itemDescriptions
    new OpenType[] {SimpleType.INTEGER,
                    SimpleType.STRING}  // itemTypes
);

The plain Java class needs a public constructor annotated with @ConstructorParameters annotation:

public class NamedNumber {
    public int getNumber() {return number;}
    public String getName() {return name;}
    @ConstructorParameters({"number", "name"})
    public NamedNumber(int number, String name) {
        this.number = number;
        this.name = name;
    }
    private final int number;
    private final String name;
}

And the equivalent with a record class:

public record NamedNumber(int number, String name) {}

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Issue

JDK-8264124: Update MXBean specification and implementation to extend mapping of CompositeType to records

Reviewers

Mandy Chung (@mlchung - Reviewer)
Chris Hegarty (@ChrisHegarty - Reviewer)
Alan Bateman (@AlanBateman - Reviewer)

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…ping of CompositeType to records

bridgekeeper · 2021-03-25T17:31:11Z

👋 Welcome back dfuchs! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

openjdk · 2021-03-25T17:32:41Z

@dfuch The following labels will be automatically applied to this pull request:

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mlbridge · 2021-03-25T17:37:48Z

Webrevs

dfuch · 2021-03-25T19:01:26Z

/csr needed

openjdk · 2021-03-25T19:02:08Z

@dfuch has indicated that a compatibility and specification (CSR) request is needed for this pull request.
@dfuch please create a CSR request and add link to it in JDK-8264124. This pull request cannot be integrated until the CSR request is approved.

AlanBateman · 2021-03-26T14:45:05Z

src/java.management/share/classes/javax/management/MXBean.java

+    <p>If the class is a {@link Record} and the getter is a component
+       accessor for a record component {@code name} of type <em>T</em>,
+       then the item in the {@code CompositeType} has the same name
+       than the record component, and has type <em>opentype(T)</em>.</p>


The update to the MXBean spec looks good. Do you have a typo here, I assume it should say "as the record component".

Right, thanks. Qualifying it as "a typo" was too kind ;-)
I have updated the PR. I also moved the record example after the from example to respect the order of precedence.

…to respect the logical order of precedence.

ChrisHegarty · 2021-03-26T17:07:02Z

Generally, I think that this is a good change. It nice to see that the semantics of record classes can be leverage to build the CompositeType in this way. And equally how that maps back to the canonical constructor.

mlchung · 2021-03-27T01:40:17Z

src/java.management/share/classes/javax/management/MXBean.java

@@ -753,7 +753,9 @@ another proxy (like {@code ModuleMXBean.getProduct()} which
      {@code CompositeType} is determined by the <a href="#type-names">
      type name rules</a> below.</p>

-    <p>The class is examined for getters using the conventions
+    <p>If the class is a {@link Record}, its getters are the
+      accessors for the record components. Otherwise, the


It may be good to add a link like {@linkplain RecordComponent record components}

You add record in "Mappings for other types". I think it deserves a separate section "Mappings for record classes" (maybe after primitive types). It's useful to add a row for record in the summary table above "Mappings for primitive types"

Link added. With respect to adding a section for records, it's a bit difficult to separate that from the "Mapping for other types" without a lot of duplication. I can add a row in the summary table, and then add a new section "Mapping for records" just before "Mapping for other types", that just gives a brief overview and refers to the mapping for other types below.

Something like this - what do you think?

<h3 id="records">Mappings for Records</h3> <p>A {@linkplain Record record} <em>R</em> whose {@linkplain Class#getRecordComponents() components} are all convertible to open types, is itself convertible to a {@link CompositeType} as follows. The type name of this {@code CompositeType} is determined by the same <a href="#type-names">type name rules</a> defined by the <a href="#composite-map">Mapping for other types</a> below. Its getters are the accessors for the {@linkplain RecordComponent record components}, and the record is reconstructed using its canonical constructor, without needing any annotation.</p> <p>A record may also expose additional non-canonical constructors, which can be used to reconstruct the record if the composite data does not exactly contain all the components expected by the canonical constructor. However, in order to be taken into account by the MXBean framework, such non-canonical constructors need to be annotated with either the {@link ConstructorParameters @javax.management.ConstructorParameters} or {@code @java.beans.ConstructorProperties} annotation.</p> <p>The complete rules for the mapping are detailed as part of the <a href="#composite-map">Mapping for other types</a> below.</p> <h3 id="composite-map">Mappings for other types</h3> <p>Given a record, or a Java class or interface <em>J</em> that does not match the other rules in the table above, the MXBean framework will attempt to map it to a {@link CompositeType} as follows. [....]

Hi Mandy, I have updated the PR with a revised version of the text above. Is that more in line what you had in mind?

best regards,
-- daniel

This looks better. I like a separate mapping section for records since the mapping rules are straight-forward. The complexity comes if we want to support a record to implement CompositeDataView that allows a type to support more flexible conversion to CompositeData which is why you add records in the "Mappings for other types". I am wondering if we really want to support records to implement CompositeDataView but we may want to avoid such a special case.

I suggest add subsections in "Mappings for other types": There are two mapping rules: (1) opentype(J) maps J to CompositeType (2) opendata(J) maps J to CompositeData. opentype(J) for record class does not need to refer to other types. The common cases for opendata(J) for record class is using the canonical constructors. The other less common cases like using non-canonical constructors and CompositeDataView can state that it follows the same rules as specified for other types. "Mappings for other types" does not need any change for records.

"Reconstructing an instance of Java type J from a CompositeData" section should be renamed to "Reconstructing an instance of Java type or record class J from a CompositeData"

Here is a minor tweaking on "Mappings for Records"

A record is convertible to a CompositeType if and only if all its components are convertible to open types. Otherwise, it is not convertible. A record class is converted to a CompositeType with one item for every record component as follows. - The type name of this CompositeType is determined by the type name rules detailed below. - Each record component of type T, the item in the CompositeType has the same name as the record component and of type opentype(T). The mapping from an instance of a record class to a CompositeData corresponding to the CompositeType is the same as specified as for other types (add a link). A record is reconstructed from a CompositeData using its canonical constructor. The canonical constructor doesn't require the presence of @javax.management.ConstructorParameters or @java.beans.ConstructorProperties annotations. If these annotations are present on the canonical constructor, they will be ignored. If the CompositeData from which the record is reconstructed doesn't contain all the record components, the MXBean framework will attempt to reconstruct the record in the same way as specified for other types (add a link).

I have updated the PR with those changes, plus a few minor adjustments.

…mproved test.

mlchung

Thanks for making the change. The spec change looks good to me.

dfuch · 2021-04-08T09:25:10Z

@mlchung @AlanBateman @ChrisHegarty would you formally approve the fix? The CSR has been approved.

openjdk · 2021-04-08T21:22:14Z

@dfuch This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8264124: Update MXBean specification and implementation to extend mapping of CompositeType to records

Reviewed-by: mchung, chegar, alanb

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 95 new commits pushed to the master branch:

627ad9f: 8262328: Templatize JVMFlag boilerplate access methods
c15680e: 8264868: Reduce inclusion of registerMap.hpp and register.hpp
5784f6b: 8264948: Check for TLS extensions total length
42f4d70: 8264649: runtime/InternalApi/ThreadCpuTimesDeadlock.java crash in fastdebug C2 with -XX:-UseTLAB
76bd313: 8264872: Dependencies: Migrate to PerfData counters
07c8ff4: 8264871: Dependencies: Miscellaneous cleanups in dependencies.cpp
863feab: 8005295: Use mandated information for printing of repeating annotations
f26cd2a: 8264997: Remove SystemDictionary::cache_get
9ebc497: 8264765: BreakIterator sees bogus sentence boundary in parenthesized “i.e.” phrase
ec31b3a: 8264727: Shenandoah: Remove extraneous whitespace from phase timings report
... and 85 more: https://git.openjdk.java.net/jdk/compare/6c145c47683dd0073b9669acc24ed114443a50fa...master

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mlchung

This looks okay to me but I'm not that familiar with the existing implementation. The test case covers the important cases.

AlanBateman

Spec and implementation changes look good.

dfuch · 2021-04-12T16:30:38Z

/integrate

openjdk · 2021-04-12T16:31:57Z

@dfuch Since your change was applied there have been 109 commits pushed to the master branch:

714ae54: 8258788: incorrect response to change in window insets [lanai]
f479437: 8265082: test/hotspot/jtreg/gc/g1/TestG1SkipCompaction.java fails validate-source
27f4b27: 8264623: Change to Xcode 12.4 for building on Macos at Oracle
7c20d97: 8265052: Break circular include dependency in objArrayOop.inline.hpp
b90ad76: 8233567: [TESTBUG] FocusSubRequestTest.java fails on macos
125184e: 8265012: Shenandoah: Backout JDK-8264718
be0d46c: 8262068: Improve G1 Full GC by skipping compaction for regions with high survival ratio
f71be8b: 8264954: unified handling for VectorMask object re-materialization during de-optimization
3c9858d: 8264827: Large mapped buffer/segment crash the VM when calling isLoaded
e604320: 8264783: G1 BOT verification should not verify beyond allocation threshold
... and 99 more: https://git.openjdk.java.net/jdk/compare/6c145c47683dd0073b9669acc24ed114443a50fa...master

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8264124: Update MXBean specification and implementation to extend map…

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…ping of CompositeType to records

openjdk bot added the rfr Pull request is ready for review label Mar 25, 2021

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AlanBateman reviewed Mar 26, 2021

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Fixed typo. Moved example with record after example with from method …

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…to respect the logical order of precedence.

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dfuch added 10 commits March 30, 2021 16:36

Integrated review feedback. Added a section for Mapping to records.

8e5a70c

Integrated review feedback. Updated the section for Mapping to records.

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Merge branch 'master' into mxbeans-8264124

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Minor tweaks. Improved test.

2a75f25

Merge branch 'master' into mxbeans-8264124

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Moved mapping for records just before Mapping for MXBean interface; I…

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…mproved test.

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8264124: Update MXBean specification and implementation to extend mapping of CompositeType to records #3201

8264124: Update MXBean specification and implementation to extend mapping of CompositeType to records #3201

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8264124: Update MXBean specification and implementation to extend mapping of CompositeType to records #3201

8264124: Update MXBean specification and implementation to extend mapping of CompositeType to records #3201

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