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SanjanaMahapatraSanjanaMahapatra
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feat(jdk14): Add demo for JEP 366 – Deprecate the ParallelScavenge + SerialOld GC Combination code changes (#346)
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‎src/main/java/org/javademos/init/Java14DemoLoader.java‎

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import org.javademos.java14.jep362.SolarisSparcRemovalDemo;
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import org.javademos.java14.jep364.ZGarbageCollectorOnMacOS;
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import org.javademos.java14.jep365.ZGarbageCollectorOnWindows;
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import org.javademos.java14.jep366.ParallelScavengeGCCombinationDemo;
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import org.javademos.java14.jep368.TextBlockSecondPreviewDemo;
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import org.javademos.java14.jep370.ForeignMemoryAccessDemo;
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demos.put(362, new SolarisSparcRemovalDemo());
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demos.put(364, new ZGarbageCollectorOnMacOS());
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demos.put(365, new ZGarbageCollectorOnWindows());
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demos.put(366, new ParallelScavengeGCCombinationDemo());
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demos.put(368, new TextBlockSecondPreviewDemo());
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demos.put(370, new ForeignMemoryAccessDemo());
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}

‎src/main/java/org/javademos/java14/jep366/ParallelScavengeGCCombinationDemo.java‎

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package org.javademos.java14.jep366;
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import org.javademos.commons.IDemo;
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import java.lang.management.*;
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import java.util.ArrayList;
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import java.util.List;
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/// Demo for JDK 14 feature <strong>JEP 366 - Deprecate the ParallelScavenge + SerialOld GC Combination</strong>.
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///
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///
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/// Summary:
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/// Deprecate the combination of the Parallel Scavenge and Serial Old garbage collection algorithms.
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///
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/// Further Reading -
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/// - [Official JEP 366](https://openjdk.org/jeps/366)
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///
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/// Additional References -
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/// - [DZone - Java 14](https://dzone.com/refcardz/java-14-1)
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/// - [New Features in Java 14](https://www.baeldung.com/java-14-new-features)
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///
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///
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/// @author SanjanaMahapatra
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public class ParallelScavengeGCCombinationDemo implements IDemo {
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@Override
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public void demo() {
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info(366);
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// In the oracle documentation, it states that very few people uses the pairing
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// combination of parallel young generation GC (called ParallelScavenge) and the
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// serial old GC (called SerialOld).
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// To use this feature, this has to be explicitly specified and enabled by the
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// user with usage of following command - XX:+UseParallelGC -XX:-UseParallelOldGC
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// using the command line options.
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// This combination is only useful, only when there is a need of deployment which
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// involves very large young generation and a very small old generation.
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// This involves a very rare and risky deployment, since a slight shift in liveness for objects
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// in the young generation will result in an OutOfMemoryException, since the old generation is
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// significantly smaller than the young generation.
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// Since, this is a rarely used combination of GC algorithms, and requires significant
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// maintenance effort, Java 14 have deprecated this feature.
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// Lets demonstrates one example and check in the terminal
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System.out.println("=== JEP 366: Deprecate ParallelScavenge + SerialOld GC Combination ===");
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// Example 1: Showing the deprecation warning
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System.out.println("""
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1. Running with deprecated GC combination:
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Command: java -XX:+UseParallelGC -XX:-UseParallelOldGC -version
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Expected: Deprecation warning in Java 14+
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"""
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);
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// Show current GC information
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System.out.println("Demonstrating with example");
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// allocate a memory to trigger the Garbage Collection (GC)
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List<byte[]> largeMemory = new ArrayList<>(2000);
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try {
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for(int i =0; i < 100_000; i++) {
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largeMemory.add(new byte[500 * 1024 * 1024]);
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System.out.println(" === Allocated memory : " + ((i+1)*500) + " MB ===");
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Thread.sleep(50);
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}
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}catch (OutOfMemoryError err) {
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System.out.println(" === OutOfMemoryError occurred === ");
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}catch (InterruptedException err) {
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Thread.currentThread().interrupt();
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}
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printGCInfo();
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}
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private void printGCInfo() {
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Runtime runtime = Runtime.getRuntime();
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System.out.println("Max Memory: " + runtime.maxMemory() / (1024 * 1024) + "MB");
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System.out.println("Total Memory: " + runtime.totalMemory() / (1024 * 1024) + "MB");
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System.out.println("Free Memory: " + runtime.freeMemory() / (1024 * 1024) + "MB");
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System.out.println("Used Memory: " + (runtime.totalMemory() - runtime.freeMemory()) / (1024 * 1024) + " MB");
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// Get GC information
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try {
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System.out.println("\n=== GARBAGE COLLECTORS ===");
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List<GarbageCollectorMXBean> gcBeans =
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ManagementFactory.getGarbageCollectorMXBeans();
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for(GarbageCollectorMXBean gcBean : gcBeans) {
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System.out.println("GC Name: " + gcBean.getName());
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System.out.println("Collection Count: " + gcBean.getCollectionCount());
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System.out.println("Collection Time: " + gcBean.getCollectionTime());
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}
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System.out.println("\n === Memory Usage Distribution === ");
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MemoryMXBean m = ManagementFactory.getMemoryMXBean();
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for(MemoryType type: MemoryType.values()) {
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usage(type, type == MemoryType.HEAP?
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m.getHeapMemoryUsage(): m.getNonHeapMemoryUsage());
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System.out.println();
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for(MemoryPoolMXBean mp: ManagementFactory.getMemoryPoolMXBeans())
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if(mp.getType() == type) usage(mp.getName(), mp.getUsage());
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System.out.println();
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}
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System.out.println("\n === Memory Pools Used === ");
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List<MemoryPoolMXBean> memoryPoolMXBeanList = ManagementFactory.getMemoryPoolMXBeans();
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for(MemoryPoolMXBean poolMXBean : memoryPoolMXBeanList) {
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MemoryUsage memoryUsage = poolMXBean.getUsage();
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String name = poolMXBean.getName();
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System.out.println("Pool Name: " + name);
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System.out.printf(" - Init: %,dMB%n", memoryUsage.getInit() / (1024 * 1024));
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System.out.printf(" - Used: %,dMB%n", memoryUsage.getUsed() / (1024 * 1024));
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System.out.printf(" - Committed: %,dMB%n", memoryUsage.getCommitted() / (1024 * 1024));
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System.out.printf(" - Max: %,dMB%n", memoryUsage.getMax() / (1024 * 1024));
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// Classify the pool
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if (name.contains("Eden") || name.contains("Young")) {
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System.out.println(" - Type: Young Generation (Eden)");
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} else if (name.contains("Survivor")) {
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System.out.println(" - Type: Young Generation (Survivor)");
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} else if (name.contains("Old") || name.contains("Tenured")) {
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System.out.println(" - Type: Old Generation");
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} else if (name.contains("Metaspace")) {
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System.out.println(" - Type: Metaspace");
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} else if (name.contains("Code")) {
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System.out.println(" - Type: Code Cache");
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}
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}
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calculateGenerationTotals(memoryPoolMXBeanList);
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} catch (Exception e) {
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System.out.println("Unable to get GC details");
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}
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}
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private static void usage(Object header, MemoryUsage mu) {
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long used = mu.getUsed(), max = mu.getMax();
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System.out.printf(
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max > 0? "%-30s %,d (%,d MiB) of %,d (%,d MiB)%n": "%-30s %,d (%,d MiB)%n",
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header, used, used >>> 20, max, max >>> 20);
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}
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private void calculateGenerationTotals(List<MemoryPoolMXBean> memoryPools) {
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long youngGenUsed = 0;
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long youngGenCommitted = 0;
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long youngGenMax = 0;
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long oldGenUsed = 0;
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long oldGenCommitted = 0;
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long oldGenMax = 0;
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for (MemoryPoolMXBean pool : memoryPools) {
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MemoryUsage usage = pool.getUsage();
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String name = pool.getName();
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if (name.contains("Eden") || name.contains("Survivor") ||
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name.contains("Young") || name.contains("PS Young")) {
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youngGenUsed += usage.getUsed();
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youngGenCommitted += usage.getCommitted();
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if (usage.getMax() != -1) {
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youngGenMax += usage.getMax();
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}
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} else if (name.contains("Old") || name.contains("Tenured") ||
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name.contains("PS Old")) {
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oldGenUsed += usage.getUsed();
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oldGenCommitted += usage.getCommitted();
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if (usage.getMax() != -1) {
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oldGenMax += usage.getMax();
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}
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}
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}
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System.out.println("\n=== CALCULATED GENERATION TOTALS ===");
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System.out.printf("Young Generation:%n");
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System.out.printf(" - Used: %,dMB%n", youngGenUsed / (1024 * 1024));
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System.out.printf(" - Committed: %,dMB%n", youngGenCommitted / (1024 * 1024));
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if (youngGenMax > 0) {
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System.out.printf(" - Max: %,dMB%n", youngGenMax / (1024 * 1024));
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}
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System.out.printf("Old Generation:%n");
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System.out.printf(" - Used: %,dMB%n", oldGenUsed / (1024 * 1024));
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System.out.printf(" - Committed: %,dMB%n", oldGenCommitted / (1024 * 1024));
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if (oldGenMax > 0) {
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System.out.printf(" - Max: %,dMB%n", oldGenMax / (1024 * 1024));
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}
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if (youngGenCommitted > 0 && oldGenCommitted > 0) {
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double youngRatio = (double) youngGenCommitted / (youngGenCommitted + oldGenCommitted) * 100;
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double oldRatio = (double) oldGenCommitted / (youngGenCommitted + oldGenCommitted) * 100;
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System.out.printf("Generation Ratio: Young=%.1f%%, Old=%.1f%%%n", youngRatio, oldRatio);
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}
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}
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}

‎src/main/resources/JDK14Info.json‎

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"link": true,
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"code": false
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},
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{
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"jep": 366,
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"jdk": 14,
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"name": "JEP 366 - Deprecate the ParallelScavenge + SerialOld GC Combination",
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"dscr": "Deprecate the combination of the Parallel Scavenge and Serial Old garbage collection algorithms.",
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"link": false,
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"code": true
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},
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{
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"jep": 368,
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"jdk": 14,

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