结论：Java中ReentrantReadWriteLock对写互斥，对读共享。
import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReadWriteLock; import java.util.concurrent.locks.ReentrantReadWriteLock; public class ReadWriteLockTest { ReadWriteLock readWriteLock = new ReentrantReadWriteLock(); final Lock readLock = readWriteLock.readLock(); final Lock writeLock = readWriteLock.writeLock(); public static void main(String[] args) throws InterruptedException { // new ReadWriteLockTest().writeRead(); // new ReadWriteLockTest().readRead(); // new ReadWriteLockTest().readWrite(); // new ReadWriteLockTest().writeWrite(); new ReadWriteLockTest().writeReadWrite(); } /** * 读 -> 写。同时有写锁和读锁时，写锁必须阻塞等待读锁读完，写锁才能进去。 * @throws InterruptedException */ private void readWrite() throws InterruptedException { new Thread(new Runnable() { @Override public void run() { try { System.out.println(String.format("tid[%s]: w请求读锁", Thread.currentThread().getId())); readLock.lock(); System.out.println(String.format("tid[%s]: w获得读锁", Thread.currentThread().getId())); Thread.sleep(3000); } catch (InterruptedException e) { e.printStackTrace(); } finally { System.out.println(String.format("tid[%s]: w释放读锁", Thread.currentThread().getId())); readLock.unlock(); } } }).start(); // 为了保证顺序，休眠一会再调度 Thread.sleep(100); new Thread(new Runnable() { @Override public void run() { try { System.out.println(String.format("tid[%s]: w请求写锁", Thread.currentThread().getId())); writeLock.lock(); System.out.println(String.format("tid[%s]: w获得写锁", Thread.currentThread().getId())); Thread.sleep(3000); } catch (InterruptedException e) { e.printStackTrace(); } finally { System.out.println(String.format("tid[%s]: w释放写锁", Thread.currentThread().getId())); writeLock.unlock(); } } }).start(); } /** * 写 -> 读 -> 写。 * 后面写锁是否会优先调度？答：不会，还是会按顺序调度 * @throws InterruptedException */ private void writeReadWrite() throws InterruptedException { new Thread(new Runnable() { @Override public void run() { try { System.out.println(String.format("tid[%s]: w请求写锁", Thread.currentThread().getId())); writeLock.lock(); System.out.println(String.format("tid[%s]: w获得写锁", Thread.currentThread().getId())); Thread.sleep(3000); } catch (InterruptedException e) { e.printStackTrace(); } finally { System.out.println(String.format("tid[%s]: w释放写锁", Thread.currentThread().getId())); writeLock.unlock(); } } }).start(); // 为了保证顺序，休眠一会再调度 Thread.sleep(100); new Thread(new Runnable() { @Override public void run() { try { System.out.println(String.format("tid[%s]: w请求读锁", Thread.currentThread().getId())); readLock.lock(); System.out.println(String.format("tid[%s]: w获得读锁", Thread.currentThread().getId())); Thread.sleep(3000); } catch (InterruptedException e) { e.printStackTrace(); } finally { System.out.println(String.format("tid[%s]: w释放读锁", Thread.currentThread().getId())); readLock.unlock(); } } }).start(); new Thread(new Runnable() { @Override public void run() { try { System.out.println(String.format("tid[%s]: w请求写锁", Thread.currentThread().getId())); writeLock.lock(); System.out.println(String.format("tid[%s]: w获得写锁", Thread.currentThread().getId())); Thread.sleep(3000); } catch (InterruptedException e) { e.printStackTrace(); } finally { System.out.println(String.format("tid[%s]: w释放写锁", Thread.currentThread().getId())); writeLock.unlock(); } } }).start(); } /** * 写 -> 读。同时有写锁和读锁时，读锁必须等待写锁写完后，才能获得锁 * @throws InterruptedException */ private void writeRead() throws InterruptedException { new Thread(new Runnable() { @Override public void run() { try { System.out.println(String.format("tid[%s]: w请求写锁", Thread.currentThread().getId())); writeLock.lock(); System.out.println(String.format("tid[%s]: w获得写锁", Thread.currentThread().getId())); Thread.sleep(3000); } catch (InterruptedException e) { e.printStackTrace(); } finally { System.out.println(String.format("tid[%s]: w释放写锁", Thread.currentThread().getId())); writeLock.unlock(); } } }).start(); // 为了保证顺序，休眠一会再调度 Thread.sleep(100); new Thread(new Runnable() { @Override public void run() { try { System.out.println(String.format("tid[%s]: w请求读锁", Thread.currentThread().getId())); readLock.lock(); System.out.println(String.format("tid[%s]: w获得读锁", Thread.currentThread().getId())); Thread.sleep(3000); } catch (InterruptedException e) { e.printStackTrace(); } finally { System.out.println(String.format("tid[%s]: w释放读锁", Thread.currentThread().getId())); readLock.unlock(); } } }).start(); } /** * 读 -> 读，读锁可以共享 */ private void readRead() { new Thread(new Runnable() { @Override public void run() { try { System.out.println(String.format("tid[%s]: w请求读锁", Thread.currentThread().getId())); readLock.lock(); System.out.println(String.format("tid[%s]: w获得读锁", Thread.currentThread().getId())); Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } finally { System.out.println(String.format("tid[%s]: w释放读锁", Thread.currentThread().getId())); readLock.unlock(); } } }).start(); new Thread(new Runnable() { @Override public void run() { try { System.out.println(String.format("tid[%s]: w请求读锁", Thread.currentThread().getId())); readLock.lock(); System.out.println(String.format("tid[%s]: w获得读锁", Thread.currentThread().getId())); Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } finally { System.out.println(String.format("tid[%s]: w释放读锁", Thread.currentThread().getId())); readLock.unlock(); } } }).start(); } /** * 写 -> 写。同时有写锁和写锁时，写锁必须等待上一个写锁写完后，才能获得锁 * @throws InterruptedException */ private void writeWrite() throws InterruptedException { new Thread(new Runnable() { @Override public void run() { try { System.out.println(String.format("tid[%s]: w请求写锁", Thread.currentThread().getId())); writeLock.lock(); System.out.println(String.format("tid[%s]: w获得写锁", Thread.currentThread().getId())); Thread.sleep(3000); } catch (InterruptedException e) { e.printStackTrace(); } finally { System.out.println(String.format("tid[%s]: w释放写锁", Thread.currentThread().getId())); writeLock.unlock(); } } }).start(); // 为了保证顺序，休眠一会再调度 Thread.sleep(100); new Thread(new Runnable() { @Override public void run() { try { System.out.println(String.format("tid[%s]: w请求写锁", Thread.currentThread().getId())); writeLock.lock(); System.out.println(String.format("tid[%s]: w获得写锁", Thread.currentThread().getId())); Thread.sleep(3000); } catch (InterruptedException e) { e.printStackTrace(); } finally { System.out.println(String.format("tid[%s]: w释放写锁", Thread.currentThread().getId())); writeLock.unlock(); } } }).start(); } }