一、同步锁(Lock):同步锁是一个显示锁,需要通过 lock() 上锁,通过 unlock() 释放锁
public class Test {
public static void main(String[] args) throws ExecutionException, InterruptedException {
Ticket ticket = new Ticket();
new Thread(ticket, "1号窗口").start();
new Thread(ticket, "2号窗口").start();
new Thread(ticket, "3号窗口").start();
}
}
class Ticket implements Runnable {
private int tickets = 100;
private Lock lock = new ReentrantLock();
@Override
public void run() {
// 加锁
lock.lock();
try {
while (tickets > 0) {
Thread.sleep(100);
System.out.println(Thread.currentThread().getName() + " 完成售票,余票为:" + --tickets);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
// 释放锁
lock.unlock();
}
}
}
二、闭锁(CountDownLatch):在要完成某些运算时,只有其它线程的运算全部运行完毕,当前运算才继续下去。
例如:计算线程的执行时间
public class Test {
public static void main(String[] args) {
// 闭锁计数器和其它线程数一样
final CountDownLatch latch = new CountDownLatch(5);
LatchDemo ld = new LatchDemo(latch);
long start = System.currentTimeMillis();
for (int i = 0; i < 5; i++) {
// 其它运算线程开始执行
new Thread(ld).start();
}
try {
// 主线程等待其它线程全部执行完,才继续下去,算出线程执行时间
latch.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
long end = System.currentTimeMillis();
System.out.println("耗时:" + (end - start));
}
}
// 其它运算线程
class LatchDemo implements Runnable {
private CountDownLatch latch;
LatchDemo(CountDownLatch latch) {
this.latch = latch;
}
@Override
public void run() {
synchronized (this) {
try {
for (int i = 0; i < 50000; i++) {
if (i % 2 == 0) {
System.out.println(i);
}
}
} finally {
// 闭锁每次减一
latch.countDown();
}
}
}
}