lock接口认识及可重入锁的实现
Lock接口中有lockInterruptibly方法（线程中断）,tryLock方法（获取锁成功返回成功，获取锁失败返回失败）,还有就是锁的公平性问题，还有就是提供读写性能的ReadWriteLock等等。
Lock需要显示地获取和释放锁，繁琐，能让代码更加灵活
Synchronized不需要显示地获取和释放锁，简单。
使用Lock可以方便的实现公平性
非阻塞的获取锁
能被中断的获取锁
超时获取锁
1 public class Sequence { 2 3 private int value; 4 5 Lock lock = new ReentrantLock(); 6 7 8 public int getNext() { 9 lock.lock(); 10 int a = value ++; 11 lock.unlock(); 12 return a; 13 } 14 15 16 public static void main(String[] args) { 17 Sequence s = new Sequence(); 18 new Thread(new Runnable() { 19 @Override 20 public void run() { 21 while(true) { 22 System.out.println(Thread.currentThread().getName()+ " "+s.getNext()); 23 24 try { 25 Thread.sleep(100); 26 } catch (InterruptedException e) { 27 // TODO Auto-generated catch block 28 e.printStackTrace(); 29 } 30 } 31 } 32 }).start(); 33 34 35 new Thread(new Runnable() { 36 @Override 37 public void run() { 38 while(true) { 39 System.out.println(Thread.currentThread().getName()+ " "+s.getNext()); 40 41 try { 42 Thread.sleep(100); 43 } catch (InterruptedException e) { 44 // TODO Auto-generated catch block 45 e.printStackTrace(); 46 } 47 } 48 } 49 }).start(); 50 } 51 52 }
2，可重入锁的实现
//Demo.java
public class Demo { MyLock lock = new MyLock(); public void a() { lock.lock(); //1 System.out.println("a"); b(); lock.unlock(); //4 } public void b() { lock.lock(); //2 System.out.println("b"); lock.unlock(); //3 } public static void main(String[] args) { Demo d = new Demo(); new Thread(new Runnable() { @Override public void run() { d.a(); } }).start(); } }
1 public class MyLock implements Lock { 2 3 private boolean isLocked = false; 4 5 private Thread lockBy = null; 6 7 int lockCount = 0; 8 9 @Override 10 public synchronized void lock() { 11 12 Thread currentThread = Thread.currentThread(); //1,第一个线程Thread-0 islocked = false 13 //2 thread-0再次进入lock方法 当前线程还是thread-0 14 while(isLocked && currentThread != lockBy) //1，跳过 2，islock=true ,currentThread = lockby,跳过 15 try { 16 wait(); 17 } catch (InterruptedException e) { 18 e.printStackTrace(); 19 } 20 isLocked = true; //1 21 lockBy = currentThread; //1把当前线程指定为lockby 22 lockCount ++; //1 lockCount=1 23 //2 lockCount =2 24 25 } 26 27 28 29 @Override 30 public synchronized void unlock() { 31 if(lockBy == Thread.currentThread()) { 32 lockCount --; // 3 ,lockcount = 1 33 //4 lockcount = 0 34 if(lockCount == 0 ) { 35 notify(); //4 36 isLocked =false; //4 37 } 38 } 39 40 } 41 42 43 44 @Override 45 public void lockInterruptibly() throws InterruptedException { 46 // TODO Auto-generated method stub 47 48 } 49 50 @Override 51 public boolean tryLock() { 52 // TODO Auto-generated method stub 53 return false; 54 } 55 56 @Override 57 public boolean tryLock(long time, TimeUnit unit) throws InterruptedException { 58 // TODO Auto-generated method stub 59 return false; 60 } 61 62 63 @Override 64 public Condition newCondition() { 65 // TODO Auto-generated method stub 66 return null; 67 } 68 69 }
