The VM specification
NO LONGER
makes any reference to JLS (Java Lang Spec)

Project Coin

• Strings in Switch
• Binary Literals
• int x = Integer.parseInt("1100110", 2); ==> int x = 0b1100110;
• long anotherLong = 2_147_483_648L;
• int bitPattern = 0b0001_1100__0011_0111__0010_1011__1010_0011;
• Multi-Catch
• catch (FileNotFoundException|ParseException|ConfigurationException e)
• Try With Resources
• try ( OutputStream out = new FileOutputStream(file); InputStream is = url.openStream() ) {
• Diamond Syntax
• Earlier: Map<Integer, Map<String, String>> usersLists = new HashMap<Integer, Map<String, String>>();
• Now: Map<Integer, Map<String, String>> usersLists = new HashMap<>();

What are the few limitations of Java 6 I/O?

What are the few limitations of Java 6 I/O?

• Performance
• There is no direct class or method support for navigating directory trees
• There is no way of detecting and dealing with symbolic links
• It’s not possible to read the attributes (such as readable, writable, or execut- able) of a file in one easy operation

• DirectoryStream Interface: try (DirectoryStream<Path> stream = Files.newDirectoryStream(dir))
• FileVisitor Interface: SimpleFileVisitor

Use the Future objects isDone() method

Event style programming

• Main usecase: large files
• Sockets: AsynchronousSocketChannel, AsynchronousServerSocketChannel

Why do we use Spring framework?
What is the main feature that frameworks like Spring/EJB provide?

Why do we use Spring framework?
What is the main feature that frameworks like Spring/EJB provide?

• Inversion of Control
• Dependency Injection

JSR-330

• javax.inject
• @Inject, @Qualifier, @Named, @Scope, and @Singleton
• Guice 3 is the full RI for JSR-330

A static block takes a lock on what?

A static block takes a lock on what?


'Class' object

A method takes a lock on what?

A method takes a lock on what?


this

A static method takes a lock on what?

A static method takes a lock on what?


'Class' object

Are locks in Java re-entrant?

Are locks in Java re-entrant?


Yes. thread holding a lock that encounters a synchronization point for the same lock will be allowed to continue

JMM: Synchronizes-with: “releases happen before acquires”

JMM: Happens-before: usecases: program order and synchronizes-with

Features of Java JMM

• Objects can be easily shared between all threads
• Objects can be changed by any threads that have a reference
• thread scheduler can swap threads on and off cores at any time
• Methods must be able to be swapped out while they’re running
• Objects can be locked

Concurrency Design Concepts

• Safety: self consistent regardless of operations
• Liveness: eventually progresses or fails
• Performance
• Reusability

Please explore java.util.concurrent package

Classloading

Classloaders

Method Handles and Method Types

• java.lang.invoke
• Logger lgr = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());
• Better than reflection and proxies

Within Class Files...

• Java has 200 opcodes - each is a SINGLE byte
• Bytecode goes through JIT => conversion to machine level code
• Types of opcodes:
  • Load and Store
  • Arithmetic
  • Execution control
  • Invocation - method calling - invokedynamic

A Digression into Performance

What is LATENCY?

What is LATENCY?

Latency is the end-to-end time taken to process a single work-unit at a given workload

What is THROUGHPUT?

What is THROUGHPUT?

Throughput is the number of units of work that a system can perform in some time period with given resources

What is UTILIZATION?

What is UTILIZATION?

Utilization represents the percentage of available resources that are being used to han- dle work units, instead of housekeeping tasks

What is EFFICIENCY?

What is EFFICIENCY?

The efficiency of a system is equal to the throughput divided by the resources used

What is CAPACITY?

What is CAPACITY?

Capacity is the number of work units (such as transactions) that can be in flight through the system at any time

What is SCALABILITY?

What is SCALABILITY?

Change in throughput or latency as resources are added is the scalability of a system

What is DEGRADATION?

What is DEGRADATION?

At what point and by how much the scale begins to tip

Memory speed has improved more slowly than CPUs have added transistors, which means there’s a risk that the processing cores will fall idle due to not having the relevant data on hand to process

Memory Latency Hierarchy

• Registers
• L1, L2, L3 Caches
• RAM
• SSD
• HDD

Hardware techniques like instruction-level parallelism (ILP) and chip multithreading (CMT), were used to try to keep the CPU operating on data, even in the face of the widening gap between CPU capability and memory latency
So, a large portion of CPU power is consumed in caching and data-locality and NOT in application processing
This means the future of application performance is intimately tied to good concurrency programming - get your skills right

Clocks


How many exist? And how do you get them?

Clocks

• RTC (Real Time Clock) - Keeps running when PC is switched off
• 8254 - System.currentTimeMillis()
• TSC (Time Stamp Counter) - System.nanoTime() - good only for delta's
• HPET (High Precision Event Timers)

And these clocks DRIFT AWAY

Areas of Memory


How many exist?

Areas of Memory

• Eden - Young Gen
• Survivor - Young Gen
• Tenured - Old Gen
• PermGen - Not actually Heap

Garbage Collection (GC)


How many exist?

Garbage Collection (GC)

• Serial Collector
• Parallel Collector: Use the cores! But... still... STW
• Parallel Compacting Collector: Mark, Summary, Compaction - Old Gen Special, Regions within generations, Density calculation
• Concurrent Mark and Sweep Collector: Initial Mark, Concurrent Mark, ReMark, Sweep
  • False Negatives Okay - due to concurrent marking
  • Eventual Full Collections are inevitable
• G1 - The new one!

G1

• Pause Goals
• Regions in Heap itself - non-contiguous heap for each generation
• G1 will only collect as many regions as it has time
• Any generation can be collected to reach pause goal
• Good read - G1: One Garbage Collector To Rule Them All
• Least fragmentation with region size config

JVM


How many do you know?

JVM

• HotSpot
• JRockit
• Dalvik
• Azul Zing - Dr. Cliff Clicks JVM
• Wiki - http://en.wikipedia.org/wiki/List_of_Java_virtual_machines

Polyglot Programming

• Groovy
• Scala
• Clojure
• And the CRAP - JRuby, Jython, Rhino

Polyglot

My Hypothesis

• Learn Concurrency, else you will perish
• Java will Shrink in JVM. Are you ready?
• Talk Numbers. Else, someone who can, will get the better job

Thank you!!