线程锁Lock
Lock 相当于 当前对象的 Synchronized
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import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock; /* * Lock lock = new ReentrantLock(); * lock.lock(); lock.unLock(); * 类似于 synchronized，但不能与synchronized 混用 */public class LockTest { public static void main(String[] args) { final Outer outer = new LockTest().new Outer(); new Thread(new Runnable() { @Override public void run() { // TODO Auto-generated method stub while (true) { outer.out1("zhangxiaoxiao"); outer.out2("lihuoming"); } } }).start(); new Thread(new Runnable() { @Override public void run() { // TODO Auto-generated method stub while (true) { outer.out1("zhangxiaoxiao"); outer.out2("lihuoming"); } } }).start(); } class Outer { Lock lock = new ReentrantLock(); void out1(String name) { lock.lock(); int len = name.length(); for (int i = 0; i < len; i++) { System.out.print(name.charAt(i)); } System.out.println(); lock.unlock(); } void out2(String name) { lock.lock(); int len = name.length(); for (int i = 0; i < len; i++) { System.out.print(name.charAt(i)); } System.out.println(); lock.unlock(); } } } |
读写锁 ReentrantReadWriteLock
读写锁：允许多条线程同时读；不能读中有写；不能写中有读；不能写中有写
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import java.util.HashMap; import java.util.Map; import java.util.concurrent.locks.ReadWriteLock; import java.util.concurrent.locks.ReentrantReadWriteLock; /* * 问题：设计一个 缓存机制 的 伪代码 * 从集合中读取数据，读取不到，就写入，再考虑多线程并发的情况 */ public class ReadWriteLockTest2 { private Map<String, Object> data = new HashMap<String, Object>(); private ReadWriteLock lock = new ReentrantReadWriteLock(); //读写锁 public Object getInstance1(String key, Object obj) { lock.readLock().lock(); Object value = null; try { value = data.get(key); if (value == null) {//一条线程进入这里， lock.readLock().unlock();//读锁解了，其他线程就可能也到这了 lock.writeLock().lock();//只能有一条线程到这，写锁开启，要写入数据了 if (data.get(key) == null) { value = obj; /*先判断数据，如果不存在，才写入，，因为 界时当写锁解除后，其他 线程，再想写入时， 判断到数据存在 ，就跳过了。就不会发生同时写入的情况 */ data.put(key, value); } lock.writeLock().unlock();//写完了，解锁 lock.readLock().lock(); } } finally { lock.readLock().unlock(); } return value; } |
