关于Lock锁

以前都没注意到锁，一直用着 synchronized 以为就万事大吉了。

   突然发现还有另外一种，而且另外一种针对于读取的操作（资源竞争激烈）更具有优势

 

    先上代码：

package test.thread;

import java.util.concurrent.locks.ReentrantReadWriteLock;

public class LSThreadTest {

    private int j = 0;
    private ReentrantReadWriteLock rwl = new ReentrantReadWriteLock();

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        LSThreadTest tt = new LSThreadTest();
        Inc inc = tt.new Inc();
        Dec dec = tt.new Dec();
        Sel sel = tt.new Sel();

        Thread thread = new Thread(inc);
        thread.start();
        thread = new Thread(dec);
        thread.start();

        for (int i = 0; i < 4; i++) {
            thread = new Thread(sel);
            thread.start();
        }
    }

    private void inc() {
        rwl.writeLock().lock();
        try {
            j++;
            System.out.println(Thread.currentThread().getName() + "    j:" + j);
        } catch (Exception e) {
            // TODO: handle exception
            e.printStackTrace();
        } finally {
            rwl.writeLock().unlock();
        }

    }

    private void dec() {
        rwl.writeLock().lock();
        try {
            j--;
            System.out.println(Thread.currentThread().getName() + "    j:" + j);
        } catch (Exception e) {
            // TODO: handle exception
            e.printStackTrace();
        } finally {
            rwl.writeLock().unlock();
        }
    }

    class Inc implements Runnable {
        public void run() {
            for (int i = 0; i < 10; i++) {
                inc();
            }
        }
    }

    class Dec implements Runnable {
        public void run() {
            for (int i = 0; i < 10; i++) {
                dec();
            }
        }
    }

    private void sel() {
        rwl.readLock().lock();
        try {
            System.out.println(Thread.currentThread().getName() + "    j:" + j);
        } catch (Exception e) {
            // TODO: handle exception
            e.printStackTrace();
        } finally {
            rwl.readLock().unlock();
        }
    }

    class Sel implements Runnable {
        public void run() {
            for (int i = 0; i < 10; i++) {
                sel();
            }
        }
    }
}

     

ReentrantReadWriteLock 在 写锁的时候，是不会被打扰到。同时在读的时候却是可以一起读。