线程间通信Lock的awaitsignal

- 日理万妓 2022-09-11 01:18 67阅读 0赞

JUC中提供了Condition对象, 用于让指定线程等待与唤醒, 按照预期顺序执行, 它必须和ReentrantLock重入锁配合使用

Conddition用于替代wait() / notify()方法

notify 只能随机唤醒等待的线程, 而Condition可以唤醒指定的线程, 这样有利于更好的控制并发程序

# **Condition核心方法** #

await() - 阻塞当前线程, 直到signal唤醒

signal() - 唤醒被await的线程, 从中断处继续执行

signalAll() - 唤醒所有被await() 阻塞的线程

package com.dongguo.concurrent.lock;
    
    import java.util.concurrent.locks.Condition;
    import java.util.concurrent.locks.Lock;
    import java.util.concurrent.locks.ReentrantLock;
    
    /** * @author Dongguo * @date 2021/9/3 0003-14:36 * @description: Lock实现生产者消费者 */
    public class ThreadLockUnlockDemo { 
        public static void main(String[] args) { 
            Number number = new Number();
            new Thread(() -> { 
                for (int i = 0; i < 10; i++) { 
                    try { 
                        //为了体现出虚假唤醒问题
                        Thread.sleep(200);
                        number.incry();
                    } catch (InterruptedException e) { 
                        e.printStackTrace();
                    }
                }
            }, "t1").start();
            new Thread(() -> { 
                for (int i = 0; i < 10; i++) { 
                    try { 
                        Thread.sleep(300);
                        number.decry();
                    } catch (InterruptedException e) { 
                        e.printStackTrace();
                    }
                }
            }, "t2").start();
            new Thread(() -> { 
                for (int i = 0; i < 10; i++) { 
                    try { 
                        Thread.sleep(400);
                        number.incry();
                    } catch (InterruptedException e) { 
                        e.printStackTrace();
                    }
                }
            }, "t3").start();
            new Thread(() -> { 
                for (int i = 0; i < 10; i++) { 
                    try { 
                        Thread.sleep(500);
                        number.decry();
                    } catch (InterruptedException e) { 
                        e.printStackTrace();
                    }
                }
            }, "t4").start();
        }
    }
    
    class Number { 
        private int count;
        private Lock lock = new ReentrantLock();
        private Condition condition = lock.newCondition();
    
        public void incry() throws InterruptedException { 
            try { 
                lock.lock();
                while (count != 0) { 
                    condition.await();
                }
                count++;
                System.out.println(Thread.currentThread().getName() + "加一成功，count值为：" + count);
                condition.signalAll();
            } catch (InterruptedException e) { 
                e.printStackTrace();
            } finally { 
                lock.unlock();
            }
        }
    
        public synchronized void decry() throws InterruptedException { 
            try { 
                lock.lock();
                while (count == 0) { 
                    condition.await();
                }
                count--;
                System.out.println(Thread.currentThread().getName() + "减一成功，count值为：" + count);
                condition.signalAll();
            } catch (InterruptedException e) { 
                e.printStackTrace();
            } finally { 
                lock.unlock();
            }
        }
    }

运行结果：

t1加一成功，count值为：1
    t2减一成功，count值为：0
    t1加一成功，count值为：1
    t2减一成功，count值为：0
    t3加一成功，count值为：1
    t4减一成功，count值为：0
    t1加一成功，count值为：1
    t2减一成功，count值为：0
    t1加一成功，count值为：1
    t2减一成功，count值为：0
    t3加一成功，count值为：1
    t4减一成功，count值为：0
    t1加一成功，count值为：1
    t2减一成功，count值为：0
    t1加一成功，count值为：1
    t4减一成功，count值为：0
    t3加一成功，count值为：1
    t2减一成功，count值为：0
    t1加一成功，count值为：1
    t2减一成功，count值为：0
    t1加一成功，count值为：1
    t4减一成功，count值为：0
    t3加一成功，count值为：1
    t2减一成功，count值为：0
    t1加一成功，count值为：1
    t2减一成功，count值为：0
    t1加一成功，count值为：1
    t4减一成功，count值为：0
    t3加一成功，count值为：1
    t2减一成功，count值为：0
    t3加一成功，count值为：1
    t4减一成功，count值为：0
    t3加一成功，count值为：1
    t4减一成功，count值为：0
    t3加一成功，count值为：1
    t4减一成功，count值为：0
    t3加一成功，count值为：1
    t4减一成功，count值为：0
    t3加一成功，count值为：1
    t4减一成功，count值为：0