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。
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