Eclipse Collections An Inside Look March 2016 Copyright © 2016 Goldman Sachs. All rights reserved.

A GENDA Agenda What is Eclipse Collections? Eclipse Collections vs others Eclipse Collections by examples UnifiedMap : The memory saver UnifiedSet : It is a Set not a Map 2

What is Eclipse Collections? Copyright © 2016 Goldman Sachs. All rights reserved.

E CLIPSE C OLLECTIONS What is Eclipse Collections Eclipse Collections −Feature rich Java Collections framework Eclipse Foundation −Eclipse Collections released under EDL and EPLEDLEPL Open for contributionscontributions Eclipse Collections Kata −Tutorial developed to learn the framework 4

Eclipse Collections vs Others Copyright © 2016 Goldman Sachs. All rights reserved.

E CLIPSE C OLLECTIONS VS OTHERS Eclipse Collections vs Others 6 FeaturesEC 7.0.0Java 8GuavaTroveScala Rich API  InterfacesReadable, Mutable, Immutable, FixedSize, Lazy Mutable, StreamMutable, FluentMutableReadable, Mutable, Immutable, Lazy Optimized Set & Map  (+Bag)  Immutable Collections  Primitive Collections  (+Bag, +Immutable)  Multimaps  (+Bag, +SortedBag)  (+Linked)(Multimap trait) Bags (Multisets)  BiMaps  Iteration StylesEager/Lazy, Serial/Parallel Lazy, Serial/Parallel Lazy, Serial Eager, Serial Eager/Lazy, Serial/Parallel (Lazy Only)

E CLIPSE C OLLECTIONS VS J AVA 8 S TREAMS Eclipse Collections vs Java 8 Streams 7 Eclipse Collections  Eager & Lazy, Serial & Parallel  Memory efficient containers  Primitive containers (all 8)  Immutable containers  More container types  More iteration patterns  “With” method patterns  “target” method patterns  Covariant return types  Java 5+ compatible Eclipse Collections  Eager & Lazy, Serial & Parallel  Memory efficient containers  Primitive containers (all 8)  Immutable containers  More container types  More iteration patterns  “With” method patterns  “target” method patterns  Covariant return types  Java 5+ compatible Java 8 Streams -Functional APIs -Lazy only -Single use -Serial & Parallel -Primitive streams (3 types) -Extensible Collectors Java 8 Streams -Functional APIs -Lazy only -Single use -Serial & Parallel -Primitive streams (3 types) -Extensible Collectors

Eclipse Collections by Example Copyright © 2016 Goldman Sachs. All rights reserved.

UnifiedMap: The memory saver Copyright © 2016 Goldman Sachs. All rights reserved.

H ASH M AP HashMap 10 JDK HashMap is backed by an Entry Entry holds key, value, next and hash transient Node [] table Node implements Map.Entry

U NIFIED M AP UnifiedMap EC UnifiedMap is backed by an array protected transient Object[] table Key, value in consecutive slots improves cache locality 11

U NIFIED M AP The Unification /** * Entry objects are not stored in the table * like in java.util.HashMap. Instead of trying * to deal with collisions in the main array * using Entry objects, we put a special object * in the key slot and put a regular Object[] * in the value slot. The array contains the * key value pairs in consecutive slots, just * like the main array, but it's a linear list * with no hashing. * The final result is a Map implementation * that's leaner than java.util.HashMap and * faster than Trove's THashMap. The best of * both approaches unified together, and thus * the name UnifiedMap. */ 12

U NIFIED M AP UnifiedMap public V get(Object key) { int index = this.index(key); Object cur = this.table[index]; if (cur != null) { Object val = this.table[index + 1]; if (cur == CHAINED_KEY) { return this.getFromChain((Object[])val,(K)key); } if (this.nonNullTableObjectEquals(cur, (K) key)) { return (V) val; } } return null; } 13

M EMORY C OMPARISON Comparing Maps Save half the memory 14

P ERFORMANCE C OMPARISON Comparing Maps Map.get() JMH Tests ElementOps/sec – higher the better 15

P ERFORMANCE C OMPARISON Comparing Maps Map.put() JMH Tests (non-presized) ElementOps/sec – higher the better 16

P ERFORMANCE C OMPARISON Comparing Maps Map.put() JMH Tests (presized) ElementOps/sec – higher the better 17

UnifiedSet: It is a Set not a Map Copyright © 2016 Goldman Sachs. All rights reserved.

H ASH S ET HashSet 19 JDK HashSet is backed by HashMap private transient HashMap map Values in each (key, value) pair are a waste of space Key, value pairs in HashMap are wrapped in an Entry leading to additional memory wastage

U NIFIED S ET UnifiedSet 20 EC UnifiedSet is backed by an array protected transient Object[] table Not backed by Map

M EMORY C OMPARISON Comparing Sets Save 4x the memory 21

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Appendix – More Features Copyright © 2016 Goldman Sachs. All rights reserved.

M ORE F EATURES The “as” methods (O(1) cost) 24

M ORE F EATURES The “to” methods (O(n) cost) 25

M ORE F EATURES Handling Exceptions 26 Using Java Collections Using Eclipse Collections

Appendix – Primitive Specialization Copyright © 2016 Goldman Sachs. All rights reserved.

P RIMITIVE S PECIALIZATION Primitive Object Boxing is expensive −Reference + Header + alignment −Wrapper classes are immutable Unboxing is expensive 28

P RIMITIVE S PECIALIZATION Primitive Object From Oracle Java guide “You can’t put an int (or other primitive value) into a collection. Collection s can only hold object references, so you have to box primitive values into the appropriate wrapper class. An Integer is not a substitute for an int ; autoboxing and unboxing blur the distinction between primitive types and reference types, but they do not eliminate it.” Source:

P RIMITIVE S PECIALIZATION List Java has object and primitive arrays Java 8 has primitive Stream s −They cannot be stored in a field −They are not reusable Java does not have primitive List s, Set s, Map s 30

P RIMITIVE S PECIALIZATION Primitive Lists 31 intList longList shortList floatList doubleList charList byteList booleanList Primitive Sets are similar Primitive Maps have combination of primitives

P RIMITIVE S PECIALIZATION Primitive Lists – Memory Comparison 32

P RIMITIVE S PECIALIZATION Primitive Sets – Memory Comparison 33

P RIMITIVE S PECIALIZATION Primitive Maps – Performance Comparison 34

P RIMITIVE S PECIALIZATION Primitive Maps – Memory Comparison 35

Appendix – Resources Copyright © 2016 Goldman Sachs. All rights reserved.

R ESOURCES Resources 37 Eclipse Collections Home Page Eclipse Collections on GitHub GS Collections Memory Benchmark collections/presentations/GSC_Memory_Tests.pdf Conference Talks and Meetups collections/wiki/Conference-talks-and-meetups