ReadWriteLock读写锁实现类为ReentrantReadWriteLock。用于控制读写数据,一次只有一个线程( 写入线程)可以修改共享数据,任何数量的线程都可以同时读取数据。
通过readLock()控制读数据,writeLock()控制写数据。
public class ReadWrite { public static void main(String[] args) { Cache cache = new Cache(); for (int i = 0; i < 3; i++) { final String t = String.valueOf(i); new Thread(()->{ try { cache.write(t,t); } catch (InterruptedException e) { e.printStackTrace(); } }).start(); } for (int i = 0; i < 3; i++) { final String t = String.valueOf(i); new Thread(()->{ cache.read(t); }).start(); } } } class Cache{ private volatile Map<String,Object> map = new HashMap<>(); private ReadWriteLock readWriteLock = new ReentrantReadWriteLock(); public void write(String key,Object value) throws InterruptedException { // 写,同一时刻只有一个线程写 readWriteLock.writeLock().lock(); try { System.out.println(Thread.currentThread().getName()+" writing..."); map.put(key,value); TimeUnit.MILLISECONDS.sleep(100); System.out.println(Thread.currentThread().getName()+" write over"); } catch (Exception e) { e.printStackTrace(); } finally { readWriteLock.writeLock().unlock(); } } public void read(String key){ // 读,多个线程可以同时读 readWriteLock.readLock().lock(); try { System.out.println(Thread.currentThread().getName()+" reading..."); System.out.println(Thread.currentThread().getName()+" value:"+map.get(key)); } catch (Exception e) { e.printStackTrace(); } finally { readWriteLock.readLock().unlock(); } } }
Thread-1 writing... Thread-1 write over Thread-0 writing... Thread-0 write over Thread-2 writing... Thread-2 write over Thread-4 reading... Thread-4 value:1 Thread-5 reading... Thread-3 reading... Thread-5 value:2 Thread-3 value:0