Fix java.library.path in VectorScorerBenchmark

[ChrisHegarty]

When adding the native int7 vector scorer a benchmark was also added. The benchmark requires the java.library.path to the set so that it can locate the native libraries. Not just the libvec.so, but also libc, systemd, etc, since they are required once the Elasticsearch native module is initialised.

The problem is that the benchmark does not correctly add the library path (nor does it depend upon the native module, which it should), it just does this (in benchmarks/build.gradle):

 systemProperty 'java.library.path', file("../libs/native/libraries/build/platform/${platformName()}-${os.arch}")

, which is not sufficient for finding libc or systemd on some Linux distributions. Consequently, the benchmark fails to run. Unless one was to patch it with something like this:

diff --git a/benchmarks/build.gradle b/benchmarks/build.gradle
@@ -76,7 +76,8 @@ tasks.named("run").configure {
   executable = "${BuildParams.runtimeJavaHome}/bin/java"
   args << "-Dplugins.dir=${buildDir}/plugins" << "-Dtests.index=${buildDir}/index"
   dependsOn "copyExpression", "copyPainless"
-  systemProperty 'java.library.path', file("../libs/native/libraries/build/platform/${platformName()}-${os.arch}")
+  systemProperty 'java.library.path', file("/usr/lib/x86_64-linux-gnu/:../libs/native/libraries/build/platform/linux-x64")
 }

For testing, the native library is configured in ElasticsearchJavaBasePlugin, through a TestUtil.getTestLibraryPath. Would be great if we could modify the benchmark's run task to have the library path set correctly, or somehow use TestUtil.getTestLibraryPath directly.

To reproduce the problem, just run the benchmark on Linux, say Ubuntu (aarch64 for now, until x64 support is added):

./gradlew -p benchmarks run --args "org.elasticsearch.benchmark.vector.VectorScorerBenchmark -p dims=1024"

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[ChrisHegarty]

More repo steps:

// build localDistro as a convenience to get a local JDK and build the native libs, e.g.
./gradlew localDistro
export RUNTIME_JAVA_HOME=/home/ubuntu/git/elasticsearch/build/distribution/local/elasticsearch-8.14.0-SNAPSHOT/jdk/

// enable logging, e.g.
$ git diff benchmarks/src/main/resources/log4j2.properties
@@ -4,5 +4,5 @@ appender.console.layout.type = PatternLayout
 appender.console.layout.pattern = [%d{ISO8601}][%-5p][%-25c] [%node_name]%marker %m%n

 # Do not log at all if it is not really critical - we're in a benchmark
-rootLogger.level = error
+rootLogger.level = debug
 rootLogger.appenderRef.console.ref = console

// run the benchmark
./gradlew -p benchmarks run --args "org.elasticsearch.benchmark.vector.VectorScorerBenchmark -p dims=1024"
...
[2024-05-07T14:04:49,404][WARN ][org.elasticsearch.nativeaccess.NativeAccess] [
ode_name] Unable to load native provider. Native methods will be disabled.
java.lang.UnsatisfiedLinkError: Could not find libsystemd.so.0 in java.library.path: /home/ubuntu/git/elasticsearch/libs/native/libraries/build/platform/linux-aarch64
        at org.elasticsearch.nativeaccess.jdk.JdkSystemdLibrary.findLibSystemd(JdkSystemdLibrary.java:53) ~[elasticsearch-native-8.14.0-SNAPSHOT.jar:8.14.0-SNAPSHOT]
        at org.elasticsearch.nativeaccess.jdk.JdkSystemdLibrary.<clinit>(JdkSystemdLibrary.java:29) ~[elasticsearch-native-8.14.0-SNAPSHOT.jar:8.14.0-SNAPSHOT]
...

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