- 获取锁的线程执行完该段代码,线程会释放占有的锁;
- 线程执行发生异常,此时JVM会让线程自动释放锁。
- public interface Lock {
- void lock();
- void lockInterruptibly() throws InterruptedException;
- boolean tryLock();
- boolean tryLock(long time, TimeUnit unit) throws InterruptedException;
- void unlock();
- Condition newCondition();
- }
- lock()方法用来获取锁。
- tryLock()尝试获取锁,如果成功则返回true,失败返回false(其他线程已占有锁)。这个方法会立即返回,在拿不到锁时也不会等待。
- tryLock(long time, TimeUnit unit)方法和tryLock()方法类似,只不过在拿不到锁时等待一定的时间,如果超过等待时间还拿不到锁就返回false。
- lockInterruptibly()方法比较特殊,当通过这个方法获取锁时,如果该线程正在等待获取锁,则它能够响应中断。也就是说,当两个线程同时通过lockInterruptibly()获取某个锁时,假如线程A获得了锁,而线程B仍在等待获取锁,那么对线程B调用interrupt()方法可以中断B的等待过程。
- // lock()的使用
- Lock lock = ...;
- lock.lock();
- try{
- //处理任务
- }catch(Exception ex){
- }finally{
- lock.unlock(); //释放锁
- }
- // tryLock()的使用
- Lock lock = ...;
- if(lock.tryLock()) {
- try{
- //处理任务
- }catch(Exception ex){
- }finally{
- lock.unlock(); //释放锁
- }
- }else {
- //如果不能获取锁,则直接做其他事情
- }
- // lockInterruptibly()的使用
- public void method() throws InterruptedException {
- lock.lockInterruptibly();
- try {
- //.....
- }
- finally {
- lock.unlock();
- }
- }
- public class Test {
- private ArrayList<Integer> arrayList = new ArrayList<Integer>();
- private Lock lock = new ReentrantLock(); //注意这个地方
- public static void main(String[] args) {
- final Test test = new Test();
- new Thread(){
- public void run() {
- test.insert(Thread.currentThread());
- };
- }.start();
- new Thread(){
- public void run() {
- test.insert(Thread.currentThread());
- };
- }.start();
- }
- public void insert(Thread thread) {
- lock.lock();
- try {
- System.out.println(thread.getName()+"得到了锁");
- for(int i=0;i<5;i++) {
- arrayList.add(i);
- }
- } catch (Exception e) {
- // TODO: handle exception
- }finally {
- System.out.println(thread.getName()+"释放了锁");
- lock.unlock();
- }
- }
- }
- public class Test {
- private Lock lock = new ReentrantLock();
- public static void main(String[] args) {
- Test test = new Test();
- MyThread thread1 = new MyThread(test);
- MyThread thread2 = new MyThread(test);
- thread1.start();
- thread2.start();
- try {
- Thread.sleep(2000);
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- thread2.interrupt();
- }
- public void insert(Thread thread) throws InterruptedException{
- lock.lockInterruptibly(); //注意,如果需要正确中断等待锁的线程,必须将获取锁放在外面,然后将InterruptedException抛出
- try {
- System.out.println(thread.getName()+"得到了锁");
- long startTime = System.currentTimeMillis();
- for( ; ;) {
- if(System.currentTimeMillis() - startTime >= Integer.MAX_VALUE)
- break;
- //插入数据
- }
- }
- finally {
- System.out.println(Thread.currentThread().getName()+"执行finally");
- lock.unlock();
- System.out.println(thread.getName()+"释放了锁");
- }
- }
- }
- class MyThread extends Thread {
- private Test test = null;
- public MyThread(Test test) {
- this.test = test;
- }
- @Override
- public void run() {
- try {
- test.insert(Thread.currentThread());
- } catch (InterruptedException e) {
- System.out.println(Thread.currentThread().getName()+"被中断");
- }
- }
- }
3. ReadWriteLock
- public interface ReadWriteLock {
- /**
- * Returns the lock used for reading.
- */
- Lock readLock();
- /**
- * Returns the lock used for writing.
- */
- Lock writeLock();
- }
- public class Test {
- private ReentrantReadWriteLock rwl = new ReentrantReadWriteLock();
- public static void main(String[] args) {
- final Test test = new Test();
- new Thread(){
- public void run() {
- test.get(Thread.currentThread());
- };
- }.start();
- new Thread(){
- public void run() {
- test.get(Thread.currentThread());
- };
- }.start();
- }
- public void get(Thread thread) {
- rwl.readLock().lock();
- try {
- long start = System.currentTimeMillis();
- while(System.currentTimeMillis() - start <= 1) {
- System.out.println(thread.getName()+"正在进行读操作");
- }
- System.out.println(thread.getName()+"读操作完毕");
- } finally {
- rwl.readLock().unlock();
- }
- }
- }