介绍
ReentrantLock是互斥排他锁，同一时间只能有一个线程在执行任务，ReentrantLock支持锁的重入功能，虽然保证了线程的安全性，但是效率不高，实际上应该是写操作互斥，读操作共享。而jdk提供了读写锁ReentrantReadWriteLock。
公共代码（下面四种情况代码根据时间等候判断区别）
public class MyTask { private ReentrantReadWriteLock lock = new ReentrantReadWriteLock(); public void read() { try { lock.readLock().lock(); System.out.println(Thread.currentThread().getName() + " start"); Thread.sleep(10000); System.out.println(Thread.currentThread().getName() + " end"); } catch (InterruptedException e) { e.printStackTrace(); } finally { lock.readLock().unlock(); } } public void write() { try { lock.writeLock().lock(); System.out.println(Thread.currentThread().getName() + " start"); Thread.sleep(10000); System.out.println(Thread.currentThread().getName() + " end"); } catch (InterruptedException e) { e.printStackTrace(); } finally { lock.writeLock().unlock(); } } }
读读共享
public class ReadReadTest { public static void main(String[] args) { final MyTask myTask = new MyTask(); Thread t1 = new Thread(new Runnable() { @Override public void run() { myTask.read(); // 读 } }); t1.setName("t1"); Thread t2 = new Thread(new Runnable() { @Override public void run() { myTask.read(); // 读 } }); t2.setName("t2"); t1.start(); t2.start(); } } // 输出 t2 start t1 start // 10s t1 end t2 end
写写互斥
public class ReadReadTest { public static void main(String[] args) { final MyTask myTask = new MyTask(); Thread t1 = new Thread(new Runnable() { @Override public void run() { myTask.write(); // 写 } }); t1.setName("t1"); Thread t2 = new Thread(new Runnable() { @Override public void run() { myTask.write(); // 写 } }); t2.setName("t2"); t1.start(); t2.start(); } } // 输出 t1 start // 10s t1 end t2 start // 10s t2 end
读写互斥
public class ReadReadTest { public static void main(String[] args) { final MyTask myTask = new MyTask(); Thread t1 = new Thread(new Runnable() { @Override public void run() { myTask.read(); // 读 } }); t1.setName("t1"); Thread t2 = new Thread(new Runnable() { @Override public void run() { myTask.write(); // 写 } }); t2.setName("t2"); t1.start(); t2.start(); } } // 输出 t1 start // 10s t1 end t2 start // 10s t2 end
写读互斥
public class ReadReadTest { public static void main(String[] args) { final MyTask myTask = new MyTask(); Thread t1 = new Thread(new Runnable() { @Override public void run() { myTask.write(); // 写 } }); t1.setName("t1"); Thread t2 = new Thread(new Runnable() { @Override public void run() { myTask.read(); // 读 } }); t2.setName("t2"); t1.start(); t2.start(); } } // 输出 t1 start // 10s t1 end t2 start // 10s t2 end
总结
- 记住一句话：读读共享；写写、读写、写读都互斥。
