This document summarizes key features and updates related to concurrency in Java releases. It discusses basics of concurrency including Amdahl's law and challenges of concurrent programming. It then covers constructs in Java 5+ like atomic operations, locks, conditions, executors and collections. The document also summarizes the fork-join framework and parallelism features in Java 8 including streams API, common pool and completable future. It highlights updates to ConcurrentHashMap in Java 8 to support parallel operations.

1. Java Concurrency
Towards a better parallel balanced life …
● By
● - Srinivasan.raghavan@oracle.com
- Vaibhav.x.choudhary@oracle.com

2. Java Releases
JDK 1.5:
- Generics
-Concurrency
-Auto-boxing
J2SE 6:
- Collection Framework
enhancement
-Drag and Drop
-Improve IO support
J2SE 7:
- Concurrency Utilities
- Swing, -Fork/Join Pool ,
LWC&HWC
- G1
J2SE 8:
- Lambda expressions
- Stream Package
-More concurrency
Updates

3. Agenda
● Basics of concurrency
● Java Concurrent Package
● Reentanrant Lock / Performance
● Concurrent Collections
● Insight of Fork/Join
● Concurrency in Java 8
● Concurrent Collections java 8 updates

4. Basics of concurrency
● Amdhal's law
– Speedup <= 1/ (F + (1-F)/N)
● Age of multi-core processors and requirement
of parallel programming in mainstream.
● Writing concurrent programing is hard and
writing correct concurrent program is even
harder.
● Research in the field has been lead by Java
designers and the concurrency interest group

5. General Design Principles

Its the mutable state stupid

Design for immutability

Make field final unless they need to be mutable

Encapsulate to manage complexity

Guard all variables in an invariant with same
lock

Document the synchronization policy

6. Java Concurrency Constructs
● In Java 5 a set of synchronisers was built giving
more power than intrinsic locking
● Atomic operations using Compare and swap
● Non-Blocking Collections

7. Intrinsic locks vs Reentarant Locks
● Intrinsic locks are very low level constructs
● Reentarant Locks offers more features
● Fair queuing
● TryLock
● Explicit Condition Queue

8. Dead Locks avoidance with try locks

Dead Lock can be avoided using the try locks
●
Try locks can used for Probabilistic lock acquire
of the lock and exponential back-off and spin lock
●
Classic Transfer money Deadlock Problem
Typical traffic problem.

9. Condition Queues
●
Intrinsic locks can also work as condition queues
with wait and notify
●
Problem occurs when Intrinsic condition queue
may be used with more than one condition
predicate
●
Reentarant locks provides explicit condition
queues which offers more features
●
Fairness in access of the lock which reduce
contention
●
Help us create queues per condition predicate

10. Condition Queues
● Where a Lock replaces the use of synchronized
methods and statements, a Condition replaces
the use of the Object monitor methods.
● Consider a case of bounded buffer
– final Condition notFull = lock.newCondition();
– final Condition notEmpty = lock.newCondition();
● ArrayBlockingQueue provides the functionality
● A typical consumer/producer problem with
BlockingQueue.

11. Performance
Can Reentarant lock replace synchronized?
– No , There are big issues when used carelessly
– Use only when Fair queuing, probabilistic locking
and explicit condition queues are required

12. Java Synchronizers
● Executors
– Execution tasks in thread pools.
– Cyclic barrier ,Future task ,Semaphores
,Countdown latch
● Non-blocking algorithms
– AtomicInteger
– Compare and Swap (CAS)
– Writing a correct non-blocking algorithm are tough.
● Find out the code.

13. Concurrent Collection
● Copy on write array List
● Concurrent hash-map
● Blocking queues and producer – consumer
pattern

14. Fork/Join Framework
● New parallel mechanism for compute intensive
tasks, the fork-join framework.
● Runs on work-stealing algorithm.
● Approach
– Partition into subproblems.
– Create subtaks.
– Fork subtasks.
– Join subtaks.
– Compose solution.

15. Fork/Join Framework

16. Java 8 way

17. Parallelism Built In
● Parallelism is the feature built in Java 8
● U can iterate,filter, sort ,map reduce an array in
parallel
● The streams api makes heavy use of the Fork-
Join framework
● The entire set of features offered by the streams
api can be made to work in parallel by just
asking for the parallel stream
● The inherit complexity of Fork-Join framework is
handled under the hood

18. Java 8 Concurrency Changes
● Addition of fork-join common pool
● ConcurrentHashmapv8 which supports bulk
operations in parallel
● Completable future
● Changes to the Future Task implementation

19. Concurrent Hashmap
● Started as a replacement to Hashtable.
● Implements Lock stripping
● Doesn’t throw concurrent modification
exception
● Java 8 concurrenthashmap does a lot
● Built in support for parallelism
● More in the code .