java-thread

Java threading concepts

spawning a thread

To spawn a new Thread, get it executed as independent path of execution. One need 3 things :

1. Task - in the form of Runnable implementation
2. Worker - a Thread class object
3. Assigning task to the Worker - Passing task to the worker & invoking t.start()

        // java8 way to create a thread - Providing Runnable interface implementation using lambda expression
        Thread t1 = new Thread(() -> System.out.println("Creating a thread using lambda expression"));
        t1.start();

starting a thread twice - IllegalThreadStateException

extends thread vs implements runnable

getting & setting name of a thread

thread states and transitions

A thread can be in one of the following states:

• NEW
• RUNNABLE
• BLOCKED
• WAITING
• TIMED_WAITING
• TERMINATED

thread priorities

• Thread.MIN_PRIORITY = 1
• Thread.NORM_PRIORITY = 5
• Thread.MAX_PRIORITY = 10

demon thread

• Daemon threads are low-priority threads that conduct supporting tasks, whereas
• Non-Daemon threads are high-priority threads that handle particular tasks

The purpose of daemon threads is serving user threads, there’s no need to keep daemon threads running if all user threads terminate. That’s why the JVM will exit if there are only daemon threads running.

method to prevent thread execution

1. t.join()
2. t.interrupt()
3. Thread.sleep()
4. Thread.yield()

Thread interrupts - Interrupts are co-operative mechanism for indicating stop signal to a thread ( java.lang.InterruptedException )

synchronization

1. Mutual-Exclusion - sharing single resource across multiple threads

Once can achieve the synchronization effect in two ways :

• By synchronized method
• By synchronized bocks

And the Synchronized object lock could be

• Object level lock - instance method / block
• Class level lock - static method / block

2. data race - read write problem
3. deadlock

inter-thread communication

1. wait
2. notify()
3. notifyAll()

Uncaught Exception in Threads

• specific exception handler for each of the thread
• generic exception handler for all of the thread

java.util.concurrent Package

Exploring java concurrent Package

Lock & Condition

• java.util.concurrent.locks.Lock

• java.util.concurrent.locks.ReentrantLock

• java.util.concurrent.locks.ReadWriteLock

• java.util.concurrent.locks.ReentrantReadWriteLock

Callable & Future

ThreadLocal

Concurrent Collection

• CopyOnWriteArrayList

• CopyOnWriteArraySet

• BlockingQueue

• ArrayBlockingQueue

• LinkedBlockingQueue

• ConcurrentHashMap

ThreadPool

• Executors.newSingleThreadExecutor();
• Executors.newFixedThreadPool(1);
• Executors.newCachedThreadPool();
• ForkJoinPool

Synchronizers

1. Semaphore - a synchronizer to maintains set of permits
2. CountDownLatch
3. CyclicBarrier
4. SynchronousQueue
5. Exchanger
6. Phaser