Introduce multi-release JAR

This commit introduces the ability for the core Elasticsearch JAR to be
a multi-release JAR containing code that is compiled for JDK 8 and code
that is compiled for JDK 9. At runtime, a JDK 8 JVM will ignore the JDK
9 compiled classfiles, and a JDK 9 JVM will use the JDK 9 compiled
classfiles instead of the JDK 8 compiled classfiles. With this work, we
utilize the new JDK 9 API for obtaining the PID of the running JVM,
instead of relying on a hack.

For now, we want to keep IDEs on JDK 8 so when the build is in an IDE we
ignore the JDK 9 source set (as otherwise the IDE would give compilation
errors). However, with this change, running Gradle from the command-line
now requires JAVA_HOME and JAVA_9_HOME to be set. This will require
follow-up work in our CI infrastructure and our release builds to
accommodate this change.

Relates #28051

buildSrc/src/main/groovy/org/elasticsearch/gradle/BuildPlugin.groovy

@@ -158,8 +158,10 @@ class BuildPlugin implements Plugin<Project> {
             project.rootProject.ext.runtimeJavaVersion = runtimeJavaVersionEnum
             project.rootProject.ext.buildChecksDone = true
         }
+
         project.targetCompatibility = minimumRuntimeVersion
         project.sourceCompatibility = minimumRuntimeVersion
+
         // set java home for each project, so they dont have to find it in the root project
         project.ext.compilerJavaHome = project.rootProject.ext.compilerJavaHome
         project.ext.runtimeJavaHome = project.rootProject.ext.runtimeJavaHome
@@ -421,12 +423,12 @@ class BuildPlugin implements Plugin<Project> {
         }
         project.afterEvaluate {
             project.tasks.withType(JavaCompile) {
-                File gradleJavaHome = Jvm.current().javaHome
+                final JavaVersion targetCompatibilityVersion = JavaVersion.toVersion(it.targetCompatibility)
                 // we fork because compiling lots of different classes in a shared jvm can eventually trigger GC overhead limitations
                 options.fork = true
                 options.forkOptions.javaHome = new File(project.compilerJavaHome)
                 options.forkOptions.memoryMaximumSize = "1g"
-                if (project.targetCompatibility >= JavaVersion.VERSION_1_8) {
+                if (targetCompatibilityVersion == JavaVersion.VERSION_1_8) {
                     // compile with compact 3 profile by default
                     // NOTE: this is just a compile time check: does not replace testing with a compact3 JRE
                     if (project.compactProfile != 'full') {
@@ -449,8 +451,9 @@ class BuildPlugin implements Plugin<Project> {
 
                 options.encoding = 'UTF-8'
                 options.incremental = true
+
                 // TODO: use native Gradle support for --release when available (cf. https://github.com/gradle/gradle/issues/2510)
-                options.compilerArgs << '--release' << project.targetCompatibility.majorVersion
+                options.compilerArgs << '--release' << targetCompatibilityVersion.majorVersion
             }
         }
     }

server/build.gradle

@@ -36,6 +36,29 @@ publishing {
 
 archivesBaseName = 'elasticsearch'
 
+// we want to keep the JDKs in our IDEs set to JDK 8 until minimum JDK is bumped to 9 so we do not include this source set in our IDEs
+if (!isEclipse && !isIdea) {
+  sourceSets {
+    java9 {
+      java {
+        srcDirs = ['src/main/java9']
+      }
+    }
+  }
+
+  compileJava9Java {
+    sourceCompatibility = 9
+    targetCompatibility = 9
+  }
+
+  jar {
+    into('META-INF/versions/9') {
+      from sourceSets.java9.output
+    }
+    manifest.attributes('Multi-Release': 'true')
+  }
+}
+
 dependencies {
 
   compile "org.elasticsearch:elasticsearch-core:${version}"
@@ -94,6 +117,10 @@ dependencies {
   // repackaged jna with native bits linked against all elastic supported platforms
   compile "org.elasticsearch:jna:${versions.jna}"
 
+  if (!isEclipse && !isIdea) {
+    java9Compile sourceSets.main.output
+  }
+
   if (isEclipse == false || project.path == ":server-tests") {
     testCompile("org.elasticsearch.test:framework:${version}") {
       // tests use the locally compiled version of server

server/src/main/java/org/elasticsearch/monitor/jvm/JvmInfo.java

@@ -47,16 +47,6 @@ public class JvmInfo implements Writeable, ToXContentFragment {
         RuntimeMXBean runtimeMXBean = ManagementFactory.getRuntimeMXBean();
         MemoryMXBean memoryMXBean = ManagementFactory.getMemoryMXBean();
 
-        // returns the <process id>@<host>
-        long pid;
-        String xPid = runtimeMXBean.getName();
-        try {
-            xPid = xPid.split("@")[0];
-            pid = Long.parseLong(xPid);
-        } catch (Exception e) {
-            pid = -1;
-        }
-
         long heapInit = memoryMXBean.getHeapMemoryUsage().getInit() < 0 ? 0 : memoryMXBean.getHeapMemoryUsage().getInit();
         long heapMax = memoryMXBean.getHeapMemoryUsage().getMax() < 0 ? 0 : memoryMXBean.getHeapMemoryUsage().getMax();
         long nonHeapInit = memoryMXBean.getNonHeapMemoryUsage().getInit() < 0 ? 0 : memoryMXBean.getNonHeapMemoryUsage().getInit();
@@ -160,7 +150,7 @@ public class JvmInfo implements Writeable, ToXContentFragment {
 
         }
 
-        INSTANCE = new JvmInfo(pid, System.getProperty("java.version"), runtimeMXBean.getVmName(), runtimeMXBean.getVmVersion(),
+        INSTANCE = new JvmInfo(JvmPid.getPid(), System.getProperty("java.version"), runtimeMXBean.getVmName(), runtimeMXBean.getVmVersion(),
                 runtimeMXBean.getVmVendor(), runtimeMXBean.getStartTime(), configuredInitialHeapSize, configuredMaxHeapSize,
                 mem, inputArguments, bootClassPath, classPath, systemProperties, gcCollectors, memoryPools, onError, onOutOfMemoryError,
                 useCompressedOops, useG1GC, useSerialGC);

server/src/main/java/org/elasticsearch/monitor/jvm/JvmPid.java

@@ -0,0 +1,49 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.elasticsearch.monitor.jvm;
+
+import org.apache.logging.log4j.message.ParameterizedMessage;
+import org.elasticsearch.common.logging.Loggers;
+
+import java.lang.management.ManagementFactory;
+
+class JvmPid {
+
+    private static final long PID;
+
+    static long getPid() {
+        return PID;
+    }
+
+    static {
+        PID = initializePid();
+    }
+
+    private static long initializePid() {
+        final String name = ManagementFactory.getRuntimeMXBean().getName();
+        try {
+            return Long.parseLong(name.split("@")[0]);
+        } catch (final NumberFormatException e) {
+            Loggers.getLogger(JvmPid.class).debug(new ParameterizedMessage("failed parsing PID from [{}]", name), e);
+            return -1;
+        }
+    }
+
+}

server/src/main/java9/org/elasticsearch/monitor/jvm/JvmPid.java

@@ -0,0 +1,30 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.elasticsearch.monitor.jvm;
+
+import java.lang.ProcessHandle;
+
+class JvmPid {
+
+    static long getPid() {
+        return ProcessHandle.current().pid();
+    }
+
+}