许可
final Semaphore semp = new Semaphore(5);
@Override
public void run() {
try {
semp.acquire();
// 模拟线程耗时操作
Thread.sleep(2000L);
System.out.println("Job done! " + Thread.currentThread().getId());
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
semp.release();
}
}
public static void main(String[] args){
ExecutorService service = Executors.newFixedThreadPool(20);
final SemapDemo demo = new SemapDemo();
for (int i = 0; i < 20; i++) {
service.submit(demo);
}
}
}
读写分离锁, 可以大幅提升系统并行度.
示例
使用方法与ReentrantLock类似, 只是读写锁分离.
1 private static ReentrantReadWriteLock readWriteLock=new ReentrantReadWriteLock();
2 private static Lock readLock = readWriteLock.readLock();
3 private static Lock writeLock = readWriteLock.writeLock();
一种典型的场景就是火箭发射。在火箭发射前，为了保证万无一失，往往还要进行各项设备、仪器的检查。
只有等所有检查完毕后，引擎才能点火。这种场景就非常适合使用CountDownLatch。它可以使得点火线程,
等待所有检查线程全部完工后，再执行.
示例
public class CountDownLatchDemo implements Runnable{
static final CountDownLatch end = new CountDownLatch(10);
static final CountDownLatchDemo demo = new CountDownLatchDemo();
@Override
public void run() {
try {
Thread.sleep(new Random().nextInt(10) * 1000);
System.out.println("check complete!");
end.countDown();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
public static void main(String[] args) throws InterruptedException {
ExecutorService service = Executors.newFixedThreadPool(10);
for (int i = 0; i < 10; i++) {
service.submit(demo);
}
// 等待检查
end.await();
// 所有线程检查完毕, 发射火箭.
System.out.println("fire");
service.shutdown();
}
}
Cyclic意为循环，也就是说这个计数器可以反复使用。比如，假设我们将计数器设置为10。那么凑齐
第一批10个线程后，计数器就会归零，然后接着凑齐下一批10个线程.
示例
public class CyclicBarrierDemo {
public static class Soldier implements Runnable {
private String soldier;
private final CyclicBarrier cyclic;
Soldier(CyclicBarrier cyclic, String soldier) {
this.cyclic = cyclic;
this.soldier = soldier;
}
@Override
public void run() {
&n