MultithreadingJavaNotes

//This file contains my notes on Multithreading in Java.

1. Two basic ways of creating threads in Java:
a. Extend Thread Class
b. Implement Runnable interface and pass it to the constructor of the Thread class

--check
thread.start();
thread.join();

Executor Services : thread pool --Check


Basic Thread Synchronization:
If two or more thread sharing the same data, two problems may occur:
1. Data being cached
2. Thread interleaving


Volatile keyword prevents from data being cached --Check
private volatile boolean running;

synchronized keyword to prevent interleaving

Every object in Java has intrinsic lock/monitor lock/mutex --check

It's not always ideal to have just one intrinsic lock...you may want multiple locks?? --check



=============
Producer Consumer
BlockingQueue<Integer> queue = new ArrayBlockingQueue<Integer>(10);//creates an array of 10 ints
BlockingQueue class is thread safe.

queue.put(intValue); //Waits if queue is full
queue.take(); //waits if queue is empty

=================

wait() and notify()

wait() 
- hands over the control of lock of synchronized block it's called in
- method of object class. So use it with the object you're acquiring a lock with.
- use wait(timeout) cause wait() can cause thread to wait indefinitely
- wait() is more efficient than running a while loop which keeps checking a flag value
- can call wait() only in synchronized code blocks/methods  --check


notify()
- can only be called from a synchronized code block/method
- doesn't relinquish the lock like wait(). --check
  lock will be relinquished only when the current threads execution is over.

notifyall()



============
Q: Inheritance

List<Integer> list = new LinkedList<Integer>();
can list reference access methods which are defiend in LinkedList class but not in List class??
Reason of this question:
I can't use list.removeFirst();

but if the object is like below:
LinkedList<Integer> list = new LinkedList<Integer>();
then I can use list.removeFirst();

======
Semaphores
Semaphore sem = new Semaphore(10);
sem.release();
sem.acquire();


ExecutorService executor = new Executors.newCachedThreadPool();
executor.submit( new Runnable() { /*override run() method */ } );
executor.shutdown();
executor.awaitTermination(1, TimeUnit.DAYS);

======
Callable and Future



==============
Interrupting Threads
2nd tutorial in series
how to gracefully stop a thread using volatile boolean flag
: probably the best way to stop a thread in Java