Lock Condition实现生产者消费者模式

Lock与Synchronized相比的优势：

• 相比于Synchronized, Lock更加灵活，可以关联不同的Condition;
• Lock中的RenentrantLock是可重入锁；
• 可以定义优先级或者公平锁；

lock.lock（）一定要配对 lock.unlock（），并且 lock.unlock（）放在finally块中，使得任何情况下都会解锁；

await() 源码详解

• 与当前Condition对象相关联的锁被当前线程释放，处于休眠状态，直到
• 另一个线程 signal 或者 signalAll 唤醒了当前线程；
• 另一个线程中断了当前线程；
• 虚假唤醒。

/**
     * Causes the current thread to wait until it is signalled or
     * {@linkplain Thread#interrupt interrupted}.
     *
     * <p>The lock associated with this {@code Condition} is atomically
     * released and the current thread becomes disabled for thread scheduling
     * purposes and lies dormant until <em>one</em> of four things happens:
     * <ul>
     * <li>Some other thread invokes the {@link #signal} method for this
     * {@code Condition} and the current thread happens to be chosen as the
     * thread to be awakened; or
     * <li>Some other thread invokes the {@link #signalAll} method for this
     * {@code Condition}; or
     * <li>Some other thread {@linkplain Thread#interrupt interrupts} the
     * current thread, and interruption of thread suspension is supported; or
     * <li>A &quot;<em>spurious wakeup</em>&quot; occurs.
     * </ul>
     *
     * <p>In all cases, before this method can return the current thread must
     * re-acquire the lock associated with this condition. When the
     * thread returns it is <em>guaranteed</em> to hold this lock.
     *
     * <p>If the current thread:
     * <ul>
     * <li>has its interrupted status set on entry to this method; or
     * <li>is {@linkplain Thread#interrupt interrupted} while waiting
     * and interruption of thread suspension is supported,
     * </ul>
     * then {@link InterruptedException} is thrown and the current thread's
     * interrupted status is cleared. It is not specified, in the first
     * case, whether or not the test for interruption occurs before the lock
     * is released.
     *
     * <p><b>Implementation Considerations</b>
     *
     * <p>The current thread is assumed to hold the lock associated with this
     * {@code Condition} when this method is called.
     * It is up to the implementation to determine if this is
     * the case and if not, how to respond. Typically, an exception will be
     * thrown (such as {@link IllegalMonitorStateException}) and the
     * implementation must document that fact.
     *
     * <p>An implementation can favor responding to an interrupt over normal
     * method return in response to a signal. In that case the implementation
     * must ensure that the signal is redirected to another waiting thread, if
     * there is one.
     *
     * @throws InterruptedException if the current thread is interrupted
     *         (and interruption of thread suspension is supported)
     */

signal() 源码详解

• 唤醒一个等待在这个Condition对象上的线程；
• 当前线程必须持有与Condition对象相关的lock，否则抛出IllegalMonitorStateException异常。

 /**
     * Wakes up one waiting thread.
     *
     * <p>If any threads are waiting on this condition then one
     * is selected for waking up. That thread must then re-acquire the
     * lock before returning from {@code await}.
     *
     * <p><b>Implementation Considerations</b>
     *
     * <p>An implementation may (and typically does) require that the
     * current thread hold the lock associated with this {@code
     * Condition} when this method is called. Implementations must
     * document this precondition and any actions taken if the lock is
     * not held. Typically, an exception such as {@link
     * IllegalMonitorStateException} will be thrown.
     */

package thread;

import java.util.LinkedList;
import java.util.Queue;
import java.util.Random;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

//用lock，condition实现生产者消费者模式
public class ProducerConsumer2 {
    static Lock lock = new ReentrantLock();
    static Condition queueEmpty = lock.newCondition();
    static Condition queueFull = lock.newCondition();

    public static void main(String[] args) throws InterruptedException {
        Queue<Integer> queue = new LinkedList<>();
        Producer p1 = new Producer(queue);
        Consumer c1 = new Consumer(queue);
        p1.start();
        c1.start();
        p1.join();
        c1.join();

    }

    static class Producer extends Thread {
        Queue<Integer> queue;

        public Producer(Queue<Integer> queue) {
            this.queue = queue;
        }

        @Override
        public void run() {
            lock.lock();
            try {
                while (!queue.isEmpty()) {
                    queueEmpty.await();
                }
                int tmp = new Random().nextInt();
                queue.offer(tmp);
                queueFull.signalAll();
                System.out.println("Producing " + tmp);
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                lock.unlock();
            }
        }


    }

    static class Consumer extends Thread {
        Queue<Integer> queue;

        public Consumer(Queue<Integer> queue) {
            this.queue = queue;
        }

        @Override
        public void run() {
            lock.lock();
            try {
                while (queue.isEmpty()) {
                    queueFull.await();
                }
                int tmp = queue.poll();
                queueEmpty.signalAll();
                System.out.println("Consuming " + tmp);
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                lock.unlock();
            }
        }


    }
}