Condition ReentrantLock循环10次打印ABC错误分析

错误原因就是:

应该改为: 

 

输出正常：

 

A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C

import java.awt.image.VolatileImage;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class AABBCC {

    static Lock lock = new ReentrantLock();
    final static Condition condition1 = lock.newCondition();
    final static Condition condition2 = lock.newCondition();
    final static Condition condition3 = lock.newCondition();
    private volatile int state = 1;

    public static void main(String[] args) {

        AABBCC aabbcc = new AABBCC();
        Thread thread1 = new Thread(()->{
            aabbcc.print("A",1,2,condition1,condition2);
        });

        Thread thread2 = new Thread(()->{
            aabbcc.print("B",2,3,condition2,condition3);
        });

        Thread thread3 = new Thread(()->{
            aabbcc.print("C",3,1,condition3,condition1);
        });

        thread1.start();
        thread2.start();
        thread3.start();
    }


    public void print(String s,int flg,int nextState,Condition currentCondition,Condition nextCondition){
        for(int i=0;i<2;i++){
            try {
                lock.lock();
                if(flg == state){
                    System.out.println(s);
                    state = nextState;
                    nextCondition.signal();
                }
                currentCondition.await();

            }catch (Exception e){
                e.printStackTrace();
            }finally {
                lock.unlock();
            }
        }
    }

}

假如情况：thread1执行nextCondition.signal();后 thread2 thread3都已经执行完currentCondition.await();
state=1
假如外面的for循环 i<2 即循环2次:
thread1:
i=0 A signalThread2 本线程await 
i=1 await A singal i=2 A singal i=3 A singal
当thread3 singal时 打印A 本线程wait

thread2:
i=0 本线程await 
i=1 B singalThread3 本线程await 
当thread1 singal时 打印B 本线程await

thread3:
i=0  本线程await 
i=1 C singalThread1 本线程await 

那么打印结果是:
A
B
C
A
B
thread1 waiting
thread2 waiting
thread3 for循环进不去
所以最终结果是 线程1 线程2 死死地等待 程序结束不了

假如是非正常情况：thread1执行完nextCondition.signal();,thread2才开始执行if(flg == state){,thread2执行完的时候,thread3才开始执行if(flg == state){
等等情况
会打印出多种结果,但相同的是 程序都不会终止
比如以下打印结果都会出现,具体再分析原因吧,以上 只分析了2种情况: