Head toward Java 14 and Java 15
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Slide for Tech Talk #21 Java 14 and JJUG CCC 2020 Spring (aborted)
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Head toward Java 14 and Java 15
- 4. Disclaimer I'vetestedthecontentsofthisdocumentbyJDK14.0.1andJDK15 (build22)whichareavailableon jdk.java.net asmuchaspossible, butnotallofthemhavebeentested,sopleasedoanoperation confirmationbeforeyouattempttomodifyyourcode. IconfirmedtheJDKimplementationby hg.openjdk.java.net/jdk- updates/jdk14u and jdk/jdk . 4
- 9. 358:HelpfulNullPointerExceptions $ java Sample Exception in thread "main" java.lang.NullPointerException at Sample.main(Sample.java:4) 9
- 10. 4: String name = person.getName().toUpperCase(); public class Sample { public static void main(String... args){ Person person = new Person(); String name = person.getName().toUpperCase(); } static class Person { String name = null; Person() { } String getName() { return name; } } } 10
- 11. 4: String name = person[i][j][k] // <= Nullable * 4 .getPersonalInformation() // <= Nullable .getName() // <= Nullable .getFamilyName() // <= Nullable .toUpperCase(); // <= Nullable 11
- 12. -XX:+ShowCodeDetailsInExceptionMessages $ java -XX:+ShowCodeDetailsInExceptionMessages Sample Exception in thread "main" java.lang.NullPointerException: Cann at Sample.main(Sample.java:4) Exception in thread "main" java.lang.NullPointerException: Cannot invoke "String.toUpperCase()" // When because the return value of "Sample$Person.getName()" is null // What 12
- 13. Case:localvariable 3: String[] names = null; 4: names[1].toLowerCase(); $ java -XX:+ShowCodeDetailsInExceptionMessages LocalStringArray Exception in thread "main" java.lang.NullPointerException: Cannot load from object array // When because "<local1>" is null // What at LocalStringArray.main(LocalStringArray.java:4) $ javac -g LocalStringArray.java // Add all debugging information $ java -XX:+ShowCodeDetailsInExceptionMessages LocalStringArray Exception in thread "main" java.lang.NullPointerException: Cannot load from object array // When because "names" is null // What at LocalStringArray.main(LocalStringArray.java:4) 13
- 17. 363:RemovetheConcurrentMarkSweep(CMS)Garbage Collector Goodbye -XX:+UseConcMarkSweepGC Ifyousetaboveoption,JVMwilllaunchwithDefaultGC YoushouldspecifyGCalgorthimclearly OpenJDK 64-Bit Server VM warning: Ignoring option UseConcMarkSweepGC; support was removed in 14.0 17
- 19. 366:DeprecatetheParallelScavenge+SerialOldGC Combination -XX:+UseParallelGC -XX:-UseParallelOldGC 19
- 20. ToolsandAPIs 20
- 21. 349:JFREventStreaming CollecteventsfromlocalJavaprocess import java.time.Duration; import jdk.jfr.consumer.RecordingStream; public class JFRSample { public static void main(String... args) { try (RecordingStream rs = new RecordingStream()) { // Enable events JVM will collect periodically rs.enable("jdk.CPULoad") .withPeriod(Duration.ofSeconds(10)); // Registers consumer to perform on event matching a name rs.onEvent("jdk.CPULoad", System.out::println); // Nothing happens when you specify an uncollected event rs.onEvent("jdk.SafepointCleanup", System.out::println); rs.start(); } } } 21
- 22. $ java Sample jdk.CPULoad { startTime = 18:30:06.225 jvmUser = 1.96% jvmSystem = 0.10% machineTotal = 16.56% } jdk.CPULoad { startTime = 18:30:07.239 jvmUser = 0.26% jvmSystem = 0.03% machineTotal = 16.60% } : 22
- 24. Useconfigurationinsteadofenablingeventsbyyourself import jdk.jfr.Configuration; import jdk.jfr.consumer.EventStream; import jdk.jfr.consumer.RecordingStream; public class JFRSample { public static void main(String... args) throws Exception { try (RecordingStream rs = new RecordingStream( // Set "default" or "profile" Configuration.getConfiguration("default"))) { // Can register action on events JVM collects by "default" rs.onEvent("jdk.CPULoad", System.out::println); rs.start(); } } } 24
- 25. CollecteventsfromremoteJavaprocessviaRepository # Launch jshell with enabling JFR $ jshell -J-XX:StartFlightRecording=maxage=15m,settings=default Started recording 1. : # Check repository path of targeted Java process (jshell) $ jcmd $(pgrep jshell) JFR.configure 14006: Current configuration: Repository path: /private/var/folders/wm/dz3pkjf11hb1mph16365hj1h0000gp/T/2020_ : -XX:FlightRecorderOptions=repository=/path/to 25
- 26. Openstreamwithrepositorypath import java.io.IOException; import java.nio.file.Path; import jdk.jfr.consumer.EventStream; public class JFRRemoteSample { public static void main(String... args) throws IOException { // Pass repository path via argument try (EventStream es = EventStream .openRepository(Path.of(args[0]))) { // Method Profiling Sample event es.onEvent("jdk.ExecutionSample", System.out::println); es.start(); } } } $ java JFRRemoteSample /private/(snip)/2020_05_14_18_57_15_15902 jdk.ExecutionSample { startTime = 19:09:55.345 sampledThread = "JFR Periodic Tasks" (javaThreadId = 13) state = "STATE_RUNNABLE" stackTrace = [ jdk.jfr.internal.PlatformRecorder.periodicTask() line: 474 jdk.jfr.internal.PlatformRecorder.lambda$startDiskMonitor$1() line: 417 jdk.jfr.internal.PlatformRecorder$$Lambda$52.1546693040.run() java.lang.Thread.run() line: 832 ] } 26
- 29. Basicusage $ jpackage --name sample --input <directory_includes_jar> --main-jar sample.jar --main-class Sample $ ls sample-* sample-1.0.dmg Withcustomruntimeimage: # Show ependent modules $ jdeps -summary Sample.class Sample.class -> java.base Sample.class -> java.desktop # Create runtime image that consists only of dependent modules $ jlink --add-modules java.base,java.desktop --output image # Create installer with custom runtime image $ jpackage --name sample --input <directory_includes_jar> --main-jar sample.jar --main-class Sample --runtime-image image 29
- 30. 352:Non‑VolatileMappedByteBuffers New jdk.nio.mapmode.ExtendedMapMode wasadded FileChannel channel = FileChannel.open(NON_VOLATITLE_PATH); // If READ only, use `READ_ONLY_SYNC` instead channel.map(ExtendedMapMode.READ_WRITE_SYNC, 0, bufferSize); 30
- 31. 370:Foreign‑MemoryAccessAPI(Incubator) non‑heap allocateDirect :upto2G( Integer.MAX_VALUE )perobject JavaNativeInterface:managememorybyyourself Unsafe.allocateMemory() :potentialremovewithoutwarning VarHandle intHandle = MemoryHandles.varHandle(int.class); try (MemorySegment segment = MemorySegment.allocateNative(100)) { MemoryAddress base = segment.baseAddress(); for (int i = 0 ; i < 25 ; i++) { intHandle.set(base.offset(i * 4), i); } } 31
- 33. 371:HiddenClasses Protectdynamicclassesagainstunpredictableaccess cannotfindbybytecodelinkageand Class::forName , Classloader::loadClass Normalclasses ClassLoader::defineClass Hiddenclasses MethodHandles.Lookup#defineHiddenClass(byte[] bytes, boolean initialize, MethodHandles.Lookup.ClassOption... options) byteから隠されたクラスを生成し、reflectiveaccessをも つlookupオブジェクトを返す このlookupオブジェクトが隠しクラスのClassオブジェク トを取得する唯一の方法 33