Java-7 ConcurrencyMasudul Haque

Thread & Process

• Allows you to run the Java Compiler at the same time that you are using an editor

Process-based multitasking

• A text editor can format text at the same time that it is printing

Thread-based multitasking

Implement Runnable interface Subclass Thread class

Defining a Thread

Life Cycle

Thread execution◦ start() – Start a thread by calling its run() method◦ run() – Entry point for the thread

Thread blocking◦ sleep() – Suspend a thread for a period of time◦ yield() – Voluntarily relinquish thread control to another

thread of the same priority

Thread Class

Thread lifetime and termination◦ isAlive() – Determine if a thread is still running◦ join() – Wait for a thread to terminate

Thread communication◦ wait() – Instructs the calling thread to give up the monitor

and sleep until some other thread enters the same monitor and calls notify()

◦ notify() – Wakes up a thread that called wait() on the same object

◦ notifyAll() – Wakes up all threads that called wait() on the same object

Thread Class

A concurrent application's ability to execute in a timely manner is known as its liveness

Deadlock describes a situation where two or more threads are blocked forever◦Starvation describes a situation where a thread

is unable to gain regular access to shared resources

◦ A thread often acts in response to the action of another thread. If the other thread's action is also a response to the action of another thread, then livelock may result.

Liveness & Deadlock

Thread interference Memory Consistency Error

Synchronization

Concurrency Utilities

• Concurrency APIs

java.util.concurrent

• Atomic data types

java.util.concurrent.atomic

• Locks for synchronization

java.util.concurrent.locks

Synchronizer

• Implements the classic semaphore

Semaphore

• Waits until a specified number of events have occurred

CountDownLatch

• Enables a group of threads to wait at a predefined execution point

CyclicBarrier

• Exchanges data between two threads

Exchanger

Executor

Executor

ExecutorService

ThreadPool Executor

ScheduledPool Executor

Future

Callable

Executor Interface◦ Executor◦ ExecutorService◦ SheduledThreadExecutorService

Fork/Join Thread Pools

◦ ThreadPoolExecutor◦ ScheduledThreadPoolExecutor

Executors

Concurrent Collections

Concurrent HashMap

Concurrent LinkedQueue

CopyOnWrite ArrayList

Array BlockingQueue

Concurrent SkipListMap

Concurrent SkipListSet

CopyOnWrite ArraySet

DelayQueue

LinkedBlocking Deque

LinkedBlocking Queue

Prioirty BlockingQueue

Synchronous Queue

TimeUnit Enumeration

TimeUnit Enumeratio

n

DAYS

HOURS

MINUTES

SECONDS

MICRO SECOND

S

MILLI SECOND

S

NANO SECON

DS

Lock

Lock

ReentrantLock

ReadWriteLock

Reentrant ReadWriteLo

ck

Atomic Operations

AtomicInteger

AtomicLong

decrementAndGet() compareAndSet()

addAndGet()

Thread Safety

Thread

safe

Behaves correctly

(unambiguous)

Independent of scheduling

and interleaving

Without additional

synchronization

Thread Safety

synchronized

• The primary mechanism for synchronization

volatile• Enables the thread to bypass the

cache when accessing the data