java performance boost

©2015 GlobalLogic Inc.

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Java Performance Boost

By Andrii Antilikatorov

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Optimize or not optimize?

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Rule

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Avoid usage byte[] to String constructor (Java 6)

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Avoid usage byte[] to String constructor (Java 6)

• Update to Java 7 or later• Minimize usage of constructor

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Understanding of “switch on String”

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String Internation

String

String

StringString

String

String

String

String

String

String

StringString

Do not use String.intern() on Java 6

Internation is efficient on Java 7 and above

Works great in multithreaded code

JVM string pool is NOT thread localString

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String Deduplication

Available from Java 8 update 20

Requires G1 collector to be enabled. Optional phase of G1.

Unlikely to run on the loaded systems

Processes only strings that survived after few garbage collections

Doesn’t mean you shouldn’t use internation

String

String

StringString

String

String

String

String

String

String

StringString

String

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String Deduplication

Available from Java 8 update 20

Requires G1 collector to be enabled. Optional phase of G1.

Unlikely to run on the loaded systems

Processes only strings that survived after few garbage collections

Doesn’t mean you shouldn’t use internation

String

String

StringString

String

String

String

String

String

String

StringString

String

String before Java 7 update 6

• char [] symbols;• Offset• Count• Hash code

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String Deduplication

Available from Java 8 update 20

Requires G1 collector to be enabled. Optional phase of G1.

Unlikely to run on the loaded systems

Processes only strings that survived after few garbage collections

Doesn’t mean you shouldn’t use internation

String

String

StringString

String

String

String

String

String

String

StringString

String

String before Java 7 update 6

• char [] symbols;• Offset• Count• Hash code

This is very very long string which consumes a lot of memory…

This is very very long string which consumes a lot of memory…

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String Deduplication

Available from Java 8 update 20

Requires G1 collector to be enabled. Optional phase of G1.

Unlikely to run on the loaded systems

Processes only strings that survived after few garbage collections

Doesn’t mean you shouldn’t use internation

String

String

StringString

String

String

String

String

String

String

StringString

String

String after Java 7 update 6

• char [] symbols;• Hash code

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String Deduplication

Available from Java 8 update 20

Requires G1 collector to be enabled. Optional phase of G1.

Unlikely to run on the loaded systems

Processes only strings that survived after few garbage collections

Doesn’t mean you shouldn’t use internation

String

String

StringString

String

String

String

String

String

String

StringString

String• Serial• Parallel • Concurrent Mark Sweep (CMS) • Garbage-First (G1)

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Avoid heavy logic in static constructors

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Avoid heavy logic in static constructors

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Avoid heavy logic in static constructors

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Problem with inner classes

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Problem with inner classes

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Cost of method calls

invokestatic

invokevirtual

invokeinterface

invokespecial

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Cost of method calls

invokestatic

invokevirtual

invokeinterface

invokespecial

Dependency Injection

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Maps & Sets - Hints

Set:

Map:

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Maps & Sets - Hints

• emptyList/emptyMap/emptySet - for empty collections

• singletonList/singletonMap/singletonSet - for collections containing a single element/pair

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Performance of Date/Time entities

java.util.Date java.util.GregorianCalendar

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Performance of Date/Time entities

long

Int[]

InternationalizationArithmetic

operation

support

24 bytes 448 bytes

java.util.Date java.util.GregorianCalendar

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Performance of Date/Time entities

long

Int[]

InternationalizationArithmetic

operation

support

24 bytes 448 bytes

java.util.Date java.util.GregorianCalendar

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Synchronized block or synchronized method?

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Synchronized block or synchronized method?

0: aload_0 1: getfield 2: nop 3: iconst_m1 4: ireturn

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Synchronized block or synchronized method?

0: aload_0 1: dup 2: astore_1 3: monitorenter 4: aload_0 5: getfield 6: nop 7: iconst_m1 8: aload_1 9: monitorexit 10: ireturn 11: astore_2 12: aload_1 13: monitorexit 14: aload_2 15: athrow

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Thread-safe variants of List and Set

Manual synchronization of operations with collections

Use CopyOnWrite* collections 

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Synchronized or volatile variables?

Volatile variables are less expensive than synchronized

Volatile are thread-safe for atomic operations

Volatile acquires lock on variable, therefore not thread- safe for non-atomic operations

Synchronized blocks have no performance impact if no synchronization required

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Synchronized or volatile variables?

MESI Protocol• Modified• Exclusive• Shared• Invalid

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Summary

Architecture first

Remember rule 80/20

Don’t try to write ideal code from the beginning

Don’t create bicycles

Don’t optimize for particular platform

©2015 GlobalLogic Inc.