java并发原理实战(9)--手动实现一个可重入锁

àì夳堔傛蜴生んèń 2023-07-02 07:25 6阅读 0赞

### 文章目录 ###

*  自定义个锁
 *  测试：线程安全
 *  测试：是否可重入

# 自定义个锁 #

import java.util.concurrent.TimeUnit;
    import java.util.concurrent.locks.Condition;
    import java.util.concurrent.locks.Lock;
    
    public class MyLock implements Lock { 
    
        private boolean islock = false;
        Thread lockBy = null;
        int lockCount = 0;
        @Override
        public synchronized void lock() { 
            Thread currentThread = Thread.currentThread();
            while (islock && lockBy != currentThread){ 
                try { 
                    wait();
                } catch (InterruptedException e) { 
                    e.printStackTrace();
                }
            }
            lockBy = Thread.currentThread();
            islock = true;
            lockCount++;
    
        }
        @Override
        public synchronized void unlock() { 
            if (lockBy == Thread.currentThread()){ 
                lockCount--;
               if (lockCount == 0){ 
                   islock = false;
                   notify();
               }
            }
    
        }
    
        @Override
        public void lockInterruptibly() throws InterruptedException { 
    
        }
    
        @Override
        public boolean tryLock() { 
            return false;
        }
    
        @Override
        public boolean tryLock(long time, TimeUnit unit) throws InterruptedException { 
            return false;
        }
    
        @Override
        public Condition newCondition() { 
            return null;
        }
    }

# 测试：线程安全 #

public class Sequence { 
        private  int value;
        MyLock lock = new MyLock();
    
        public  int getNext() { 
            lock.lock();
            value++;
            lock.unlock();
            return value;
        }
    
        public static void main(String[] args) { 
            Sequence sequence = new Sequence();
    
            new Thread(() -> { 
                    while (true) { 
                        System.out.println(Thread.currentThread().getName() + " " + sequence.getNext());
                        try { 
                            Thread.sleep(100);
                        } catch (InterruptedException e) { 
                            e.printStackTrace();
                        }
                    }
                }
            ).start();
            new Thread( () -> { 
                    while (true) { 
                        System.out.println(Thread.currentThread().getName() + " " + sequence.getNext());
                        try { 
                            Thread.sleep(100);
                        } catch (InterruptedException e) { 
                            e.printStackTrace();
                        }
                    }
                }
            ).start();
            new Thread( () -> { 
                    while (true) { 
                        System.out.println(Thread.currentThread().getName() + " " + sequence.getNext());
                        try { 
                            Thread.sleep(100);
                        } catch (InterruptedException e) { 
                            e.printStackTrace();
                        }
                    }
                }
            ).start();
        }
    
    }

运行结果:  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1_size_16_color_FFFFFF_t_70]  
结果显示：线程安全

# 测试：是否可重入 #

public class Demo { 
        MyLock lock = new MyLock();
    
    
        public synchronized void a() { 
    
            lock.lock();
            System.out.println("a");
            b();
            lock.unlock();
        }
    
        public synchronized void b() { 
            lock.lock();
            System.out.println("b");
            lock.unlock();
        }
    
        public static void main(String[] args) { 
            Demo d = new Demo();
            new Thread(()-> { 
                d.a();
            }).start();
    
        }
    }

运行结果：  
![在这里插入图片描述][20200127204433614.png]  
结果证明： a方法和b方法都可以进入了，是可重入锁。

--------------------

完

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20200127204308524.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2JhaWR1XzIxMzQ5NjM1,size_16,color_FFFFFF,t_70
[20200127204433614.png]: https://img-blog.csdnimg.cn/20200127204433614.png