谈到并发,必会涉及操作系统中的线程概念,线程是CPU分配的最小单位,windows系统是抢占式的,linux是轮询式的,都需要获取CPU资源。
并行:同一时刻,两个线程都在执行。
并发:同一时刻,只有一个线程执行,但是一个时间段内,两个线程都执行了。
java中创建线程的三种方式,分别为集成Thread类、实现Runnable接口,实现Callable接口。
示例
public class ThreadTest { public static class MyThread extends Thread { @Override public void run() { System.out.println("This is a thread"); } } public static void main(String[] args) { MyThread myThread = new MyThread(); myThread.start(); } }
public class RunnableTest implements Runnable { @Override public void run() { System.out.println("Runnable!"); } public static void main(String[] args) { RunnableTest runnableTest = new RunnableTest(); new Thread(runnableTest).start(); } }
public class CallableTest implements Callable<String> { @Override public String call() throws Exception { return "Callable!"; } public static void main(String[] args) { FutureTask<String> futureTask = new FutureTask<>(new CallableTest()); new Thread(futureTask).start(); try { String result = futureTask.get(); System.out.println(result); } catch (InterruptedException e) { e.printStackTrace(); } catch (ExecutionException e) { e.printStackTrace(); } } }
CountDownLatch理解成倒计数器
场景:玩的王者荣耀,创建大乔、兰陵王、安其拉、哪吒和铠等五个玩家,主线程必须在他们都完成确认后,才可以继续运行。
public static void main(String[] args) throws InterruptedException { CountDownLatch countDownLatch = new CountDownLatch(5); Thread DaQiao = new Thread(countDownLatch::countDown); Thread LanLingWang = new Thread(countDownLatch::countDown); Thread AnQiLa = new Thread(countDownLatch::countDown); Thread NeZha = new Thread(countDownLatch::countDown); Thread Kai = new Thread(() -> { try { // 稍等,上个卫生间,马上到... Thread.sleep(1500); countDownLatch.countDown(); } catch (InterruptedException ignored) {} }); DaQiao.start(); LanLingWang.start(); AnQiLa.start(); NeZha.start(); Kai.start(); countDownLatch.await(); System.out.println("所有玩家已经就位!"); }
CyclicBarrier可以理解成同步屏障
场景:让一 组线程到达一个屏障(也可以叫同步点)时被阻塞,直到最后一个线程到达屏障时,屏障才会开门,所有被屏障拦截的线程才会继续运行。