在多线程开发中,除了synchronized这个关键字外,我们还能通过Lock接口来实现这种效果。通过Lock接口来实现
这种多线程加锁效果的好处是非常的灵活,我们不在需要对整个函数加锁,而且可以很方便的把他放在我们函数的任何
一个地方,非常的称心,而且从效率上来说,使用Lock接口要比使用synchronized关键字效率高一些,下面我们来使用
一个例子来说明这种方法的使用。
1、防止重复执行(忽略重复触发)
- ReentrantLock lock = new ReentrantLock();
- if (lock.tryLock()) { //如果已经被lock,则立即返回false不会等待,达到忽略操作的效果
- try {
- //操作
- } finally {
- lock.unlock();
- }
- }
2、同步执行,类似synchronized
- ReentrantLock lock = new ReentrantLock(); //参数默认false,不公平锁
- ReentrantLock lock = new ReentrantLock(true); //公平锁
- lock.lock(); //如果被其它资源锁定,会在此等待锁释放,达到暂停的效果
- try {
- //操作
- } finally {
- lock.unlock();
- }
3、尝试等待执行
- ReentrantLock lock = new ReentrantLock(true); //公平锁
- try {
- if (lock.tryLock(5, TimeUnit.SECONDS)) {
- //如果已经被lock,尝试等待5s,看是否可以获得锁,如果5s后仍然无法获得锁则返回false继续执行
- try {
- //操作
- } finally {
- lock.unlock();
- }
- }
- } catch (InterruptedException e) {
- e.printStackTrace(); //当前线程被中断时(interrupt),会抛InterruptedException
- }
4、可中断锁的同步执行
- ReentrantLock lock = new ReentrantLock(true); //公平锁
- lock.lockInterruptibly();
- try {
- //操作
- } catch (InterruptedException e) {
- e.printStackTrace();
- } finally {
- lock.unlock();
- }
public class Job implements Runnable { private PrintQueue printQueue; public Job(PrintQueue printQueue) { this.printQueue = printQueue; } @Override public void run() { System.out.printf("%s: 要打印一个文档 start \n", Thread.currentThread().getName()); printQueue.printJob(new Object()); System.out.printf("%s: 文档被打印出来 end \n", Thread.currentThread().getName()); } }
public class PrintQueue { private final Lock queueLock = new ReentrantLock(); public void printJob(Object document) { queueLock.lock(); Long duration = (long) (Math.random() * 10000); System.out.println(Thread.currentThread().getName() + ":在PrintQueue:打印一份文档 " + (duration / 1000) + " 秒"); try { Thread.sleep(duration); } catch (InterruptedException e) { e.printStackTrace(); } finally { queueLock.unlock(); } } public static void main(String[] args) { PrintQueue printQueue = new PrintQueue(); Thread thread[] = new Thread[10]; for (int i = 0; i < 10; i++) { thread[i] = new Thread(new Job(printQueue), "Thread " + i); } for (int i = 0; i < 10; i++) { thread[i].start(); } }