ReentrantLock的使用
package concurrent._ReentrantLock; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock; //一个关于Lock的最基本操作，lock.lock()与lock.unlock() public class MyReentrantLock { private static Lock lock = new ReentrantLock(); private static int count = 0; public static void main(String[] args) throws InterruptedException { MyReentrantLock mylock = new MyReentrantLock(); Thread a = new Thread("A"){ @Override public void run() { mylock.lockinsert(Thread.currentThread()); } }; a.start(); Thread b = new Thread("B"){ @Override public void run() { mylock.lockinsert(Thread.currentThread()); } }; b.start(); Thread c = new Thread("C"){ @Override public void run() { mylock.lockinsert(Thread.currentThread()); } }; c.start(); //等待三个线程结束后输出count的值，可以使用一个闭锁 Thread.sleep(1000); System.out.println(count); } public void lockinsert(Thread thread){ lock.lock(); //线程如果没有获得锁，就会阻塞在此处，获得锁之后才能后续操作 try{ System.out.println("线程" + thread.currentThread().getName() + "获得了锁"); for(int i = 0 ; i < 1000 ; i ++){ count++; } }catch (Exception e){ e.printStackTrace(); }finally { System.out.println("线程" + thread.currentThread().getName() + "释放了锁"); lock.unlock(); } } }
结果：
线程A获得了锁 线程A释放了锁 线程B获得了锁 线程B释放了锁 线程C获得了锁 线程C释放了锁 3000
trylock（）
package concurrent._ReentrantLock; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock; //一个关于Lock的最基本操作，lock.lock()与lock.unlock() public class MyReentrantLock1 { private static Lock lock = new ReentrantLock(); private static int count = 0; public static void main(String[] args) throws InterruptedException { MyReentrantLock1 mylock = new MyReentrantLock1(); Thread a = new Thread("A"){ @Override public void run() { mylock.trylockinsert(Thread.currentThread()); } }; a.start(); Thread b = new Thread("B"){ @Override public void run() { mylock.trylockinsert(Thread.currentThread()); } }; b.start(); Thread c = new Thread("C"){ @Override public void run() { mylock.trylockinsert(Thread.currentThread()); } }; c.start(); //等待三个线程结束后输出count的值，可以使用一个闭锁 Thread.sleep(1000); System.out.println(count); } public void trylockinsert(Thread thread){ if(lock.tryLock()){ try{ System.out.println("线程" + thread.currentThread().getName() + "已经尝试获得了锁"); for(int i = 0 ; i < 1000 ; i ++){ count++; } }catch (Exception e){ e.printStackTrace(); }finally { System.out.println("线程" + thread.currentThread().getName() + "释放了锁"); lock.unlock(); } }else{ System.out.println("线程" + thread.currentThread().getName() + "尝试获得锁失败"); } } }
结果：
线程C尝试获得锁失败 线程A尝试获得锁失败 线程B已经尝试获得了锁 线程B释放了锁 1000
修改代码，使用tryLock(time,TimeUnit)
package concurrent._ReentrantLock; import java.util.concurrent.TimeUnit; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock; public class Demo3 { private static Lock lock = new ReentrantLock(); private static int count = 0; public static void main(String[] args) throws InterruptedException { Demo3 demo = new Demo3(); Thread a = new Thread("A"){ @Override public void run() { try { demo.trylockinsert(Thread.currentThread()); } catch (InterruptedException e) { e.printStackTrace(); } } }; a.start(); Thread b = new Thread("B"){ @Override public void run() { try { demo.trylockinsert(Thread.currentThread()); } catch (InterruptedException e) { e.printStackTrace(); } } }; b.start(); Thread c = new Thread("C"){ @Override public void run() { try { demo.trylockinsert(Thread.currentThread()); } catch (InterruptedException e) { e.printStackTrace(); } } }; c.start(); //一秒钟之后中断b，这个时候b应该还在等待获得锁 Thread.sleep(1000); System.out.println("主线程尝试中断bThread"); b.interrupt(); } public void trylockinsert(Thread thread) throws InterruptedException { //线程如果没有获得锁，就会阻塞在此处，获得锁之后才能后续操作 if(lock.tryLock(4, TimeUnit.SECONDS)){ try{ System.out.println("线程" + thread.currentThread().getName() + "获 得了锁"); long now = System.currentTimeMillis(); while(System.currentTimeMillis() - now < 5000){ //让线程在while循环里面空转5秒钟 } }catch (Exception e){ e.printStackTrace(); }finally { System.out.println("线程" + thread.currentThread().getName() + "释 放了锁"); lock.unlock(); } }else{ System.out.println("线程" + thread.currentThread().getName() + "放弃了对锁的获取"); } } }
结果显示：线程A获得锁，线程B和C等待锁的释放4秒钟，但是一秒钟后b被主线程中断，C在四秒钟后放弃了对锁的获取。
线程A获 得了锁 主线程尝试中断bThread java.lang.InterruptedException at java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireNanos(AbstractQueuedSynchronizer.java:936) at java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireNanos(AbstractQueuedSynchronizer.java:1247) at java.util.concurrent.locks.ReentrantLock.tryLock(ReentrantLock.java:442) at concurrent._ReentrantLock.Demo3.trylockinsert(Demo3.java:60) at concurrent._ReentrantLock.Demo3$2.run(Demo3.java:29) 线程C放弃了对锁的获取 线程A释 放了锁
