JVM Workshop

Transcript

1. @jkubrynski / kubrynski.blog
   @jkubrynski / kubrynski.blog
   JVM DIVE FOR MERE MORTALS
   JVM DIVE FOR MERE MORTALS
   WORKSHOPS
   WORKSHOPS
   JAKUB KUBRYNSKI
   JAKUB KUBRYNSKI
   jakub@devskiller.com / @jkubrynski / https://kubrynski.blog
   

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2. $ WHOAMI
   $ WHOAMI
   14+ YEARS PROFESSIONAL EXPERIENCE
   14+ YEARS PROFESSIONAL EXPERIENCE
   DEVSKILLER CO-FOUNDER
   DEVSKILLER CO-FOUNDER
   BOTTEGA TRAINER & AUDITOR
   BOTTEGA TRAINER & AUDITOR
   DEVOXX.PL PROGRAM COMMITTEE MEMBER
   DEVOXX.PL PROGRAM COMMITTEE MEMBER
   OPENSOURCE CONTRIBUTOR
   OPENSOURCE CONTRIBUTOR
   

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3. WHO ARE YOU?
   WHO ARE YOU?
   Bytecode ?
   Hashtable vs ConcurrentHashMap
   ?
   JIT ?
   Concurrent Mark-Sweep ?
   Re ection vs MethodHandle ?
   Invokedynamic ?
   

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4. PERFORMANCE TUNING PRINCIPLES
   PERFORMANCE TUNING PRINCIPLES
   measurement
   one change at a time
   deep understanding over stackover ow.com
   hints
   

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5. JAVA VIRTUAL MACHINE
   JAVA VIRTUAL MACHINE
   

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6. LIFE CYCLE
   LIFE CYCLE
   source -> javac -> bytecode
   bytecode -> classloader -> interpreter
   interpreter -> JIT -> optimized native code
   

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7. SOURCE CODE
   SOURCE CODE
   package com.random.company.app;
   public class StringUtilsHelper {
   public boolean isEmpty(String str) {
   return str != null && str.length() > 0;
   }
   }
   

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8. JAVAC
   JAVAC
   converts source code into byte
   code
   checks
   simple optimizations
   

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9. CLASS FILE
   CLASS FILE
   ClassFile
   u4 magic; // CAFEBABE
   u2 minor_version;
   u2 major_version;
   u2 constant_pool_count;
   cp_info constant_pool[constant_pool_count-1];
   u2 access_flags;
   u2 this_class;
   u2 super_class;
   u2 interfaces_count;
   u2 interfaces[interfaces_count];
   u2 fields_count;
   field_info fields[fields_count];
   u2 methods_count;
   method_info methods[methods_count];
   u2 attributes count;
   

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10. BYTECODE
    BYTECODE
    list of operation
    codes
    $xxd -p Test.class
    ...1b04a0000504ac2a1b0464b600021b68ac...
    1b => 27 => iload_1
    04 => 4 => iconst_1
    a0 => 160 => if_icmpne 7
    04 => 4 => iconst_1
    ac => 172 => ireturn
    2a => 42 => aload_0
    1b => 27 => iload_1
    04 => 4 => iconst_1
    64 => 100 => isub
    b6 => 182 => invokevirtual #5
    1b => 27 => iload_1
    68 => 104 => imul
    ac => 172 => ireturn
    

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11. BYTECODE - MORE INFO
    BYTECODE - MORE INFO
    current usage: 239/255
    $JDK/src/hotspot/share/interpreter/bytecodes.hpp
    class sun.jvm.hotspot.interpreter.Bytecodes
    http://www.javaworld.com/article/2077233/core-java/bytecode-
    basics.html
    

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12. JAVAC DEMO
    JAVAC DEMO
    HTTPS://GITHUB.COM/JKUBRYNSKI/JVM-WORKSHOP
    HTTPS://GITHUB.COM/JKUBRYNSKI/JVM-WORKSHOP
    

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13. CLASSLOADER
    CLASSLOADER
    dynamically loads
    classes
    hierarchies
    Bootstrap classloader
    Extension classloader
    Application
    classloader
    Custom classloader
    

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14. CLASSLOADING PHASES
    CLASSLOADING PHASES
    loading -> reads class le
    linking
    verifying -> veri es bytecode correctness
    preparing -> allocates memory
    resolving -> links with classes, interfaces, elds,
    methods
    initializing -> static initializers
    

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15. INTERPRETER
    INTERPRETER
    detects the critical hot spots in the
    program
    template interpreter
    java -XX:+UnlockDiagnosticVMOptions -XX:+PrintInterpreter -version
    

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16. INTERPRETER - MORE INFO
    INTERPRETER - MORE INFO
    $JDK/src/hotspot/share/interpreter/templateTable.cpp#TemplateTable::initialize
    https://openjdk.java.net/groups/hotspot/docs/RuntimeOverview.html#Interpreter|outline
    

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17. JIT
    JIT
    Just-In-Time
    optimizes code
    compiles methods into native
    code
    -client (C1) / -server (C2)
    runs up to 20 times faster
    

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18. INLINING
    INLINING
    public String getStringFromSupplier(Supplier supplier) {
    return supplier.get();
    }
    public String businessMethod(String param) {
    Supplier stringSupplier = new StringSupplier(”my” + param);
    return getStringFromSupplier(stringSupplier);
    }
    // turns to
    public String businessMethod(String param) {
    Supplier stringSupplier = new StringSupplier(”my” + param);
    return stringSupplier.get();
    }
    

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19. UNROLLING
    UNROLLING
    private static String[] options = {"yes", "no", "true", "false"}
    public void someMethod() {
    for (String opt : options) {
    process(opt);
    }
    }
    //turns into
    public void someMethod() {
    process("yes");
    process("no");
    process("true");
    process("false");
    }
    

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20. SCALAR REPLACEMENT
    SCALAR REPLACEMENT
    public record(int x, int y) {
    Point point = new Point(x, y);
    storePoint(point);
    }
    // inlining
    public record(int x, int y) {
    Point point = new Point(x, y);
    events.store("Added point", point.x, point.y);
    }
    // scalar replacement
    public record(int x, int y) {
    events.store("Added point", x, y);
    }
    

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21. DEAD CODE ELIMINATION
    DEAD CODE ELIMINATION
    public void myMethod() {
    for (int i = 0; i < THRESHOLD; i++) {
    new String("test");
    }
    }
    // turns into
    public void myMethod() {
    }
    

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22. LOCK ELISION
    LOCK ELISION
    public void process(List users) {
    List result = new ArrayList<>();
    synchronized(result) {
    fillResult(users);
    }
    }
    //turns into
    public void process(List users) {
    List result = new ArrayList<>();
    fillResult(users);
    }
    

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23. TYPE SHARPENING
    TYPE SHARPENING
    List users = new ArrayList<>();
    // turns into
    ArrayList users = new ArrayList<>();
    

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24. ON STACK REPLACEMENT
    ON STACK REPLACEMENT
    happens when the interpreter discovers that a method is looping
    converts an interpreted stack frame into a native compiled stack
    frame
    

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25. TIERED COMPILATION
    TIERED COMPILATION
    LEVELS
    LEVELS
    0: Interpreted code
    1: Simple C1 compiled code
    2: Limited C1 compiled
    code
    3: Full C1 compiled code
    4: C2 compiled code
    

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26. WHY SHOULD I CARE?
    WHY SHOULD I CARE?
    JIT does most of the optimizations we could do manually without "obfuscating" source
    code
    Performance/load tests should run only on "hot" application
    

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27. HOW TO TRACK?
    HOW TO TRACK?
    When after restarting your app is at the full
    speed?
    $ jstat -compiler 1s
    // or
    JDK9+ => -Xlog:jit*=debug
    JDK8 => -XX:+PrintCompilation
    

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28. -XLOG:JIT
    -XLOG:JIT
    $JDK/src/hotspot/share/compiler/compileTask.cpp#CompileTask::print_impl
    const char compile_type = is_osr_method ? '%' : ' ';
    const char sync_char = is_synchronized ? 's' : ' ';
    const char exception_char = has_exception_handler ? '!' : ' ';
    const char blocking_char = is_blocking ? 'b' : ' ';
    const char native_char = is_native ? 'n' : ' ';
    compile_id, compile_type, sync_char, exception_char, blocking_char, native_char, comp_level
    [0,090s][debug][jit,compilation] 104 3 java.lang.module.ModuleDescriptor$Exports::isQualified (18 bytes)
    [0,096s][debug][jit,compilation] 122 4 java.lang.module.ModuleDescriptor$Exports::isQualified (18 bytes)
    [0,097s][debug][jit,compilation] 104 3 java.lang.module.ModuleDescriptor$Exports::isQualified (18 bytes) made not entrant
    [0,032s][debug][jit,compilation] 1 3 java.util.concurrent.ConcurrentHashMap::tabAt (22 bytes)
    [0,032s][debug][jit,inlining ] @ 15 jdk.internal.misc.Unsafe::getObjectAcquire (7 bytes)
    [0,059s][debug][jit,compilation] 35 n 0 java.lang.Object::hashCode (native)
    [0,065s][debug][jit,compilation] 41 ! 3 java.util.concurrent.ConcurrentHashMap::putVal (432 bytes)
    

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29. JIT DEMO
    JIT DEMO
    

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30. EXECUTION COMPONENTS
    EXECUTION COMPONENTS
    program
    counter
    frame
    stack
    

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31. STACK TRACE
    STACK TRACE
    "main@1" prio=5 tid=0x1 nid=NA runnable
    java.lang.Thread.State: RUNNABLE
    at io.codearte.BlockBuilder.startBlock(BlockBuilder.groovy:21)
    at io.codearte.Generator.process(Generator.java:318)
    at io.codearte.ImportantApp.do(ImportantApp.java:64)
    at sun.reflect.NativeMethodImpl.invoke(NativeMethodImpl.java:18)
    at sun.reflect.NativeMethodImpl.invoke(NativeMethodImpl.java:62)
    at java.lang.reflect.Method.invoke(Method.java:497)
    

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32. DEBUGGING
    DEBUGGING
    

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33. DEBUGGING
    DEBUGGING
    

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34. MEMORY LAYOUT
    MEMORY LAYOUT
    

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35. OBJECT LAYOUT
    OBJECT LAYOUT
    com.eshop.model.Product object internals:
    OFFSET SIZE TYPE DESCRIPTION VALUE
    0 12 (object header) N/A
    12 4 int Product.id N/A
    16 4 String Product.name N/A
    20 4 (loss due to the next object alignment)
    Instance size: 24 bytes (estimated, the sample instance is not available)
    Space losses: 0 bytes internal + 4 bytes external = 4 bytes total
    

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36. OBJECT LAYOUT
    OBJECT LAYOUT
    com.eshop.model.Product object internals:
    OFFSET SIZE TYPE DESCRIPTION VALUE
    0 12 (object header) N/A
    12 4 int Product.id N/A
    16 4 int Product.price N/A
    20 4 String Product.name N/A
    Instance size: 24 bytes (estimated, the sample instance is not available)
    Space losses: 0 bytes internal + 0 bytes external = 0 bytes total
    

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37. OBJECT LAYOUT
    OBJECT LAYOUT
    com.eshop.model.Product object internals:
    OFFSET SIZE TYPE DESCRIPTION VALUE
    0 12 (object header) N/A
    12 4 int Product.id N/A
    16 4 int Product.price N/A
    20 1 boolean Product.available N/A
    21 3 (alignment/padding gap) N/A
    24 4 String Product.name N/A
    28 4 (loss due to the next object alignment)
    Instance size: 32 bytes (estimated, the sample instance is not available)
    Space losses: 3 bytes internal + 4 bytes external = 7 bytes total
    

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38. OBJECT LAYOUT
    OBJECT LAYOUT
    com.eshop.model.Product object internals:
    OFFSET SIZE TYPE DESCRIPTION VALUE
    0 16 (object header) N/A
    16 4 int Product.id N/A
    20 4 int Product.price N/A
    24 1 boolean Product.available N/A
    25 7 (alignment/padding gap) N/A
    32 8 String Product.name N/A
    Instance size: 40 bytes (estimated, the sample instance is not available)
    Space losses: 3 bytes internal + 0 bytes external = 3 bytes total
    

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39. JAVA OBJECT LAYOUT
    JAVA OBJECT LAYOUT
    https://openjdk.java.net/projects/code-tools/jol/
    

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40. JOL DEMO
    JOL DEMO
    

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41. GARBAGE COLLECTOR
    GARBAGE COLLECTOR
    cleans memory
    important performance
    factor
    vector algorithm
    stop the world in safepoints
    

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42. GC ALGORITHMS
    GC ALGORITHMS
    Serial
    Parallel
    Concurrent Mark Sweep
    G1
    Epsilon* (No-Op) - JEP 318
    ZGC* (Low Latency) - JEP
    333
    * Experimental
    

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43. VECTOR ALGORITHM
    VECTOR ALGORITHM
    mark_gc_roots()
    for (each_root_object) {
    mark_all_referenced_objects()
    }
    for (each_object_in_memory) {
    if (is_marked_as_reacheable) {
    unmark_the_object()
    } else {
    remove_object_and_reclaim_memory()
    }
    }
    

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44. GENERATIONAL HYPOTESIS
    GENERATIONAL HYPOTESIS
    Infant mortality
    young objects are much more probable to
    die
    Idea is to process both generations
    separately
    Tenuring threshold
    

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45. GENERATIONAL HYPOTESIS
    GENERATIONAL HYPOTESIS
    Does not work for caches
    Do not keep caches in the same heap as the
    application
    Go off-heap
    

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46. DISPATCH TYPES
    DISPATCH TYPES
    invokevirtual
    invokestatic
    invokespecial
    invokedynamic
    

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47. LAMBDAS
    LAMBDAS
    generated by javac
    bootstraped by
    LambdaMetafactory
    called with invokedynamic
    

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48. LAMBDA UNDER THE HOOD
    LAMBDA UNDER THE HOOD
    BigDecimal sumCreditEntries(Client client) {
    return sumEntries(client.getAccounts(),
    account -> account.getCreditEntries());
    }
    private static java.util.List lambda$sumCreditEntries$0(com.sandbox.Account);
    private Period period;
    BigDecimal sumCreditEntries(Client client) {
    return sumEntries(client.getAccounts(),
    account -> account.getCreditEntries(period));
    }
    private java.util.List lambda$sumCreditEntries$0(com.sandbox.Account);
    BigDecimal sumCreditEntries(Client client, Period period) {
    return sumEntries(client.getAccounts(), account -> account.credit(period));
    }
    private static java.util.List lambda$sumCreditEntries$0
    (java.time.Period, com.sandbox.Account);
    

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49. METHOD REFERENCE
    METHOD REFERENCE
    SIMILAR TO LAMBDAS, BUT NO NEED TO GENERATE A METHOD
    SIMILAR TO LAMBDAS, BUT NO NEED TO GENERATE A METHOD
    BECAUSE WE'RE CALLING A METHOD
    BECAUSE WE'RE CALLING A METHOD
    

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50. BENCHMARKS
    BENCHMARKS
    CallTypes.baseline avgt 30 4.163 ± 0.009 ns/op
    CallTypes.lambda avgt 30 4.174 ± 0.015 ns/op
    CallTypes.methodRef avgt 30 4.244 ± 0.049 ns/op
    CallTypesExternal.baseline avgt 30 50.055 ± 0.275 ns/op
    CallTypesExternal.lambda avgt 30 50.980 ± 0.650 ns/op
    CallTypesExternal.methodRef avgt 30 50.655 ± 0.376 ns/op
    

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51. METHODHANDLES
    METHODHANDLES
    

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52. METHODHANDLES
    METHODHANDLES
    is not a replacement for re ection (re ection is more for introspection of classes)
    re ection does access control during invocation while MethodHandle checks all during
    lookup
    

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53. EXAMPLE
    EXAMPLE
    MethodHandle toUpperCase = MethodHandles.lookup()
    .findVirtual(String.class, "toUpperCase",
    MethodType.methodType(String.class))
    Object result = toUpperCase.invoke("test"));
    String result = (String) toUpperCase.invokeExact("test"));
    

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54. TIME TO BENCHMARK
    TIME TO BENCHMARK
    

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55. BENCHMARKS
    BENCHMARKS
    1ns = 0.000 001 ms = 0.000 000 001 s
    Benchmark Mode Cnt Score Error Units
    Invocations.baseline avgt 30 35.761 ± 0.113 ns/op
    Invocations.reflectionWithoutLookup avgt 30 41.413 ± 0.223 ns/op
    Invocations.handleWithoutLookup avgt 30 42.002 ± 1.002 ns/op
    Invocations.handleExactWithoutLookup avgt 30 38.134 ± 0.153 ns/op
    Invocations.reflection avgt 30 71.207 ± 1.558 ns/op
    Invocations.handle avgt 30 858.148 ± 18.135 ns/op
    

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56. EXCEPTIONS
    EXCEPTIONS
    public class ClientAlreadyExistsException extends Throwable {
    @Override
    public synchronized Throwable fillInStackTrace() {
    return this;
    }
    }
    

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57. EXCEPTIONS
    EXCEPTIONS
    DEEP MEANS THERE ARE 4 MORE FRAMES
    DEEP MEANS THERE ARE 4 MORE FRAMES
    Benchmark Mode Cnt Score Error Units
    Exceptions.standardExcept avgt 30 1029.919 ± 5.026 ns/op
    Exceptions.standardExceptDeep avgt 30 1121.771 ± 6.615 ns/op
    Exceptions.stacklessExcept avgt 30 18.827 ± 0.066 ns/op
    Exceptions.stacklessExceptDeep avgt 30 19.835 ± 0.053 ns/op
    

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58. STREAMS
    STREAMS
    TIME TO BENCHMARK
    TIME TO BENCHMARK
    

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59. FURTHER READING
    FURTHER READING
    Optimizing Java - Benjamin J Evans, James Gough
    The Well-Grounded Java Developer - Benjamin J. Evans, Martijn
    Verburg
    Java Performance - Charlie Hunt, Binu John
    Java Performance: The De nitive Guide - Scott Oaks
    

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60. TOOLS
    TOOLS
    jdk
    Visual VM
    Mission Control
    JPro ler
    Honest Pro ler
    Java Object
    Layout
    

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61. I WANT MORE!
    I WANT MORE!
    THE JAVA® VIRTUAL MACHINE SPECIFICATION
    THE JAVA® VIRTUAL MACHINE SPECIFICATION
    HG CLONE
    HG CLONE HTTP://HG.OPENJDK.JAVA.NET/JDK11/JDK11/
    HTTP://HG.OPENJDK.JAVA.NET/JDK11/JDK11/
    HTTP://OPENJDK.JAVA.NET/PROJECTS/CODE-TOOLS/JMH
    HTTP://OPENJDK.JAVA.NET/PROJECTS/CODE-TOOLS/JMH
    

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62. BENCHMARKS
    BENCHMARKS
    HTTPS://GITHUB.COM/JKUBRYNSKI/JVM-WORKSHOP
    HTTPS://GITHUB.COM/JKUBRYNSKI/JVM-WORKSHOP
    

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63. QUESTIONS?
    QUESTIONS?
    

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64. THANKS!
    THANKS!
    

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