The descriptions of index entries in the JDK API Specification are not deterministic. Their differences reveal an underlying bug unrelated to the goal of reproducible builds.

There are 55,782 index entries in the JDK 20 API Specification, but 56 of them get different descriptions depending on whether I run the build on my local workstation, on a remote Launchpad build machine, or in a QEMU/KVM virtual machine. Of those 56 index entries, 40 are static variables of classes in the package 'java.util.jar'.

For example, each build defines a single entry for LOCCRC in the L-Index file and in the member search index, but the descriptions for the entry differ as shown below.

Local Workstation

  LOCCRC - Static variable in class java.util.jar.JarEntry
  Search: java.util.zip.JarEntry.LOCCRC -> File not found

Remote Launchpad

  LOCCRC - Static variable in class java.util.jar.JarOutputStream
  Search: java.util.zip.JarOutputStream.LOCCRC -> File not found

Virtual Machine

  LOCCRC - Static variable in class java.util.jar.JarInputStream
  Search: java.util.zip.JarInputStream.LOCCRC -> File not found

When I list the source files of the package in directory order (unsorted) on my local workstation, JarEntry is the first class found that inherits the LOCCRC variable:

  $ ls -1U ~/opt/jdk-20/src/java.base/java/util/jar/
  JarEntry.java
  package-info.java
  JarOutputStream.java
  Attributes.java
  JarInputStream.java
  JarException.java
  JarFile.java
  JarVerifier.java
  JavaUtilJarAccessImpl.java
  Manifest.java

On the virtual machine, JarInputStream is the first such class found:

  $ ls -1U ~/opt/jdk-20/src/java.base/java/util/jar/
  JarVerifier.java
  JarInputStream.java
  JavaUtilJarAccessImpl.java
  Manifest.java
  JarOutputStream.java
  Attributes.java
  JarFile.java
  JarException.java
  package-info.java
  JarEntry.java

At first, this issue appeared to be the usual file-ordering problem of reproducible builds. Yet the LOCCRC variable is inherited by four of the classes in the 'java.util.jar' package: JarEntry, JarFile, JarInputStream, and JarOutputStream. The variable is also inherited by four classes in the 'java.util.zip' package: ZipEntry, ZipFile, ZipInputStream, ZipOutputStream.

The underlying issue is that the LOCCRC index entry, and others like it, should be listed once for each inheriting class. For LOCCRC, that would require eight entries. The problem seems to occur when documenting members inherited from classes with package access. Such members are to be documented as though they were declared in the inheriting class. See JDK-4780441 for details.

SYSTEM / OS / JAVA RUNTIME INFORMATION

System information for my local workstation running Ubuntu 20.04.4 LTS is listed below:

  $ uname -a
  Linux tower 5.15.0-46-generic #49~20.04.1-Ubuntu SMP
    Thu Aug 4 19:15:44 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux

  $ ldd --version
  ldd (Ubuntu GLIBC 2.31-0ubuntu9.9) 2.31

  $ getconf GNU_LIBPTHREAD_VERSION
  NPTL 2.31

  $ $HOME/opt/jdk-20/bin/java --version
  openjdk 20-ea 2023-03-21
  OpenJDK Runtime Environment (build 20-ea+11-661)
  OpenJDK 64-Bit Server VM (build 20-ea+11-661, mixed mode, sharing)

STEPS TO REPRODUCE

I was able to reproduce the problem by building on three different systems with the following processors:

  * Local Workstation: 4-core Intel Xeon CPU E3-1225 v5
  * Remote Launchpad: 4-core AMD EPYC-Rome Processor
  * Virtual Machine: Single-core Intel Core Processor (Skylake, IBRS)

I can't be certain that the processor played a role in the ordering of files in their directories, but it may have affected the timing of the process that created them.

EXPECTED RESULTS

The builds of the JDK are identical.

ACTUAL RESULT

The builds are different, but they differ only in their Javadoc API index files and the corresponding 'member-search-index.js' file. There are 56 entries in the index that differ:

  $ git diff --numstat --shortstat local remote
  11      11      {local => remote}/index-12.txt
  1       1       {local => remote}/index-13.txt
  5       5       {local => remote}/index-18.txt
  1       1       {local => remote}/index-19.txt
  2       2       {local => remote}/index-20.txt
  1       1       {local => remote}/index-21.txt
  22      22      {local => remote}/index-3.txt
  12      12      {local => remote}/index-5.txt
  1       1       {local => remote}/index-8.txt
   9 files changed, 56 insertions(+), 56 deletions(-)

The differences occur for index entries that are identified on my local workstation as:

  * Methods in class java.awt.BufferCapabilities.FlipContents
  * Methods in class java.time.chrono.HijrahDate
  * Methods in class jdk.incubator.vector.ByteVector
  * Static variables in class java.util.jar.JarEntry

They are:

  java.awt.BufferCapabilities.FlipContents.hashCode()
  java.awt.BufferCapabilities.FlipContents.toString()
  java.time.chrono.HijrahDate.toString()
  java.time.chrono.HijrahDate.until(Temporal, TemporalUnit)
  java.util.jar.JarEntry.CENATT
  java.util.jar.JarEntry.CENATX
  java.util.jar.JarEntry.CENCOM
  java.util.jar.JarEntry.CENCRC
  java.util.jar.JarEntry.CENDSK
  java.util.jar.JarEntry.CENEXT
  java.util.jar.JarEntry.CENFLG
  java.util.jar.JarEntry.CENHDR
  java.util.jar.JarEntry.CENHOW
  java.util.jar.JarEntry.CENLEN
  java.util.jar.JarEntry.CENNAM
  java.util.jar.JarEntry.CENOFF
  java.util.jar.JarEntry.CENSIG
  java.util.jar.JarEntry.CENSIZ
  java.util.jar.JarEntry.CENTIM
  java.util.jar.JarEntry.CENVEM
  java.util.jar.JarEntry.CENVER
  java.util.jar.JarEntry.ENDCOM
  java.util.jar.JarEntry.ENDHDR
  java.util.jar.JarEntry.ENDOFF
  java.util.jar.JarEntry.ENDSIG
  java.util.jar.JarEntry.ENDSIZ
  java.util.jar.JarEntry.ENDSUB
  java.util.jar.JarEntry.ENDTOT
  java.util.jar.JarEntry.EXTCRC
  java.util.jar.JarEntry.EXTHDR
  java.util.jar.JarEntry.EXTLEN
  java.util.jar.JarEntry.EXTSIG
  java.util.jar.JarEntry.EXTSIZ
  java.util.jar.JarEntry.LOCCRC
  java.util.jar.JarEntry.LOCEXT
  java.util.jar.JarEntry.LOCFLG
  java.util.jar.JarEntry.LOCHDR
  java.util.jar.JarEntry.LOCHOW
  java.util.jar.JarEntry.LOCLEN
  java.util.jar.JarEntry.LOCNAM
  java.util.jar.JarEntry.LOCSIG
  java.util.jar.JarEntry.LOCSIZ
  java.util.jar.JarEntry.LOCTIM
  java.util.jar.JarEntry.LOCVER
  jdk.incubator.vector.ByteVector.castShape(VectorSpecies<F>, int)
  jdk.incubator.vector.ByteVector.check(Class<F>)
  jdk.incubator.vector.ByteVector.check(VectorSpecies<F>)
  jdk.incubator.vector.ByteVector.convertShape(
      VectorOperators.Conversion<Byte, F>, VectorSpecies<F>, int)
  jdk.incubator.vector.ByteVector.convert(
      VectorOperators.Conversion<Byte, F>, int)
  jdk.incubator.vector.ByteVector.maskAll(boolean)
  jdk.incubator.vector.ByteVector.reinterpretAsDoubles()
  jdk.incubator.vector.ByteVector.reinterpretAsFloats()
  jdk.incubator.vector.ByteVector.reinterpretAsInts()
  jdk.incubator.vector.ByteVector.reinterpretAsLongs()
  jdk.incubator.vector.ByteVector.reinterpretAsShorts()
  jdk.incubator.vector.ByteVector.species()

I attached the following two files that show all of the differences:

  * index-local-vs-remote.diff - Compares 'api/index-files/*.html'
  * search-local-vs-remote.diff - Compares 'api/member-search-index.js'

I made the comparisons easier by converting the HTML files to plain text with 'w3m' and by expanding the JavaScript file using the 'js-beautify' tool, as in the examples below:

  $ w3m -dump -cols 10000 -T text/html index-12.html > index-12.txt
  $ js-beautify --end-with-newline -o search-local.js \
      member-search-index.js

SOURCE CODE FOR AN EXECUTABLE TEST CASE

I used the following shell script to narrow the scope of packages while testing:

  #!/bin/bash
  # Runs Javadoc for testing

  # The JDK home directory and its extracted source files
  jdk_dir="$HOME/opt/jdk-20"
  jdk_src="$jdk_dir/src"

  "$jdk_dir/bin/java" --patch-module jdk.javadoc=target/classes \
      jdk.javadoc.internal.tool.Main \
      --source-path "$jdk_src/java.base" \
      -d tmp/doc -notimestamp -Xdoclint:none \
      java.util.jar "$@"

WORKAROUND

I don't have a workaround, but I do have a fix. My pull request will follow shortly.