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  • Java线程:Condition

    Condition 将 Object 监视器方法(wait、notify 和 notifyAll)分解成截然不同的对象,以便通过将这些对象与任意 Lock 实现组合使用,为每个对象提供多个等待 set(wait-set)。其中,Lock 替代了 synchronized 方法和语句的使用,Condition 替代了 Object 监视器方法的使用。

    条件(也称为条件队列 或条件变量)为线程提供了一个含义,以便在某个状态条件现在可能为 true 的另一个线程通知它之前,一直挂起该线程(即让其“等待”)。因为访问此共享状态信息发生在不同的线程中,所以它必须受保护,因此要将某种形式的锁与该条件相关联。等待提供一个条件的主要属性是:以原子方式 释放相关的锁,并挂起当前线程,就像 Object.wait 做的那样。

    Condition 实例实质上被绑定到一个锁上。要为特定 Lock 实例获得 Condition 实例,请使用其 newCondition() 方法。

    import java.util.concurrent.locks.Condition;
    import java.util.concurrent.locks.Lock;
    import java.util.concurrent.locks.ReentrantLock;
    
    public class ThreeConditionCommunication {
    
        public static void main(String[] args) {
    
            final Business business = new Business();
            final int cycle = 5;
            
            new Thread(new Runnable() {
                @Override
                public void run() {
                    for (int i = 1; i <= cycle; i++) {
                        business.sub2(i);
                    }
                }
            }).start();
    
            new Thread(new Runnable() {
                @Override
                public void run() {
                    for (int i = 1; i <= cycle; i++) {
                        business.sub3(i);
                    }
                }
            }).start();
    
            for (int i = 1; i <= cycle; i++) {
                business.main(i);
            }
            
        }
    
        static class Business {
            Lock lock = new ReentrantLock();
            Condition condition1 = lock.newCondition();
            Condition condition2 = lock.newCondition();
            Condition condition3 = lock.newCondition();
            private volatile int shouldSub = 1;
    
            public void sub2(int i) {
                lock.lock();
                try {
                    while (shouldSub != 2) {
                        try {
                            condition2.await();
                        }
                        catch (Exception e) {
                            e.printStackTrace();
                        }
                    }
                    for (int j = 1; j <= 10; j++) {
                        System.out.println("sub2 thread sequence of " + j + ",loop of " + i);
                    }
                    shouldSub = 3;
                    condition3.signal();
                }
                finally {
                    lock.unlock();
                }
            }
    
            public void sub3(int i) {
                lock.lock();
                try {
                    while (shouldSub != 3) {
                        try {
                            condition3.await();
                        }
                        catch (Exception e) {
                            e.printStackTrace();
                        }
                    }
                    for (int j = 1; j <= 20; j++) {
                        System.out.println("sub3 thread sequence of " + j + ",loop of " + i);
                    }
                    shouldSub = 1;
                    condition1.signal();
                }
                finally {
                    lock.unlock();
                }
            }
    
            public void main(int i) {
                lock.lock();
                try {
                    while (shouldSub != 1) {
                        try {
                            condition1.await();
                        }
                        catch (Exception e) {
                            e.printStackTrace();
                        }
                    }
                    for (int j = 1; j <= 5; j++) {
                        System.out.println("main thread sequence of " + j + ",loop of " + i);
                    }
                    shouldSub = 2;
                    condition2.signal();
                }
                finally {
                    lock.unlock();
                }
            }
    
        }
    }
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  • 原文地址:https://www.cnblogs.com/xuekyo/p/2971707.html
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