Java 8 concurrent programming

Java 1.5 before

Concurrent achieve

• Java Green Thread

java 1.2 before the thread by os kernel restrictions, thread = process, green thread JVM is scheduled to simulate a multi-threaded environment No native thread support.

• Java Native Thread

Comparative
green threads in the thread activation than native threads and thread synchronization aspects of
the I / O performance and operational aspects of the context of the thread to be lower than the local

Programming Model

• Thread
• Runnable

Limitations (Future releases will resolve to improve this part of the defect, comparable to learn)

• The lack of native support for thread management (lack of a thread pool)
• Lack of "lock" API (only synchronized keyword)
• The lack of native support for implementation of the completion of

Alternative ways:

public static void main(String[] args){
    CompletableRunnable runnable = new CompletableRunnable();
    Thread thread = new Thread(runnable,"Sub");
    thread.start();
    thread.join(); //此处阻塞主线程等待Sub完成, 否则得到的结果不准确
    System.out.printf("[Thread: %s] is running\n", Thread.currentThread.getName());
    System.out.printf("Sub Thread is completed, result is %s\n", runnable.getCompleted());
}

private static class CompletableRunnable implements Runnable{
    private volatile boolean completed = false;

    @Override
    public void run(){
        System.out.printf("[Thread: %s] is running\n", Thread.currentThread.getName());

        completed = true;
    }

    public boolean getCompleted(){
        return completed;
    }
}

• The difficulty of obtaining the results
• Double Check Locking uncertainty (singleton)

Java 5

Concurrency Framework

• J.U.C

Programming Model

• Executor, Execurtors, ExecutorService 等
• Runnable , Callable
• Future

Java 7

Parallel Framework

• Fork/Join

Programming Model

• ForkJoinPool
• ForkJoinTask
• RecursiveAction

Future (Java 5 introduced) limit

• Can not be done by hand
• Blocking results returned
• Unable to chain multiple Future
• Future results can not merge multiple
• The lack exception handling

Java 8

Asynchronous parallel frame

• Fork/Join

Programming Model

• CompletionStage
• CompletableFuture

Other frameworks

• Spring and Guava use different ListenableFuture