Java 基础【07】线程同步锁的选择

在需要线程同步的时候如何选择合适的线程锁?

　　例：选择可以存入到常量池当中的对象，String对象等

public class SyncTest
{
    private String name = "name";
public void method(String flag)
    {
        synchronized (name)
        {
            System.out.println(flag + ", invoke method ....");
            try
            {
                Thread.sleep(1000);
            }
            catch (InterruptedException e)
            {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args)
    {
        SyncTest test1 = new SyncTest();

        SyncTest test2 = new SyncTest();

        MyThread1 myThread1 = new MyThread1();
        MyThread1 myThread2 = new MyThread1();
        myThread1.syncTest = test1;
        myThread2.syncTest = test1;

        MyThread1 myThread3 = new MyThread1();
        MyThread1 myThread4 = new MyThread1();
        myThread3.syncTest = test2;
        myThread4.syncTest = test2;

        myThread1.start();
        myThread2.start();
        myThread3.start();
        myThread4.start();

    }

}

　线程类：

public class MyThread1 extends Thread
{
    SyncTest syncTest;

    @Override
    public void run()
    {
        syncTest.method(this.getName());
    }

}

　本来应该是要实现线程thread1和thread2同步，线程thread3和thread4同步的，但结果呢?

　　却是使得线程thread1、thread2、thread3、thread4同步了，很是郁闷。

　　我推荐选用的同步锁对象：

public class SyncTest
{
    // 特殊的instance变量,用于充当同步锁的对象
    private byte[] lock = new byte[0];

    public void method(String flag)
    {
        synchronized (lock)
        {
            System.out.println(flag + ", invoke method f....");
            try
            {
                Thread.sleep(1000);
            }
            catch (InterruptedException e)
            {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args)
    {
        SyncTest test1 = new SyncTest();

        SyncTest test2 = new SyncTest();

        MyThread1 myThread1 = new MyThread1();
        MyThread1 myThread2 = new MyThread1();
        myThread1.syncTest = test1;
        myThread2.syncTest = test1;

        MyThread1 myThread3 = new MyThread1();
        MyThread1 myThread4 = new MyThread1();
        myThread3.syncTest = test2;
        myThread4.syncTest = test2;

        myThread1.start();
        myThread2.start();
        myThread3.start();
        myThread4.start();

    }
}

　推荐使用0长度的byte数组充当同步锁对象，不会产生很诧异的错误同时不会占用很大内存。