线程通信用来保证线程协调运行,一般在做线程同步的时候才需要考虑线程通信的问题。
1、传统的线程通信
通常利用Objeclt类提供的三个方法:
wait() 导致当前线程等待,并释放该同步监视器的锁定,直到其它线程调用该同步监视器的notify()或者notifyAll()方法唤醒线程。
notify(),唤醒在此同步监视器上等待的线程,如果有多个会任意选择一个唤醒
notifyAll() 唤醒在此同步监视器上等待的所有线程,这些线程通过调度竞争资源后,某个线程获取此同步监视器的锁,然后得以运行。
这三个方法必须由同步监视器对象调用,分为两张情况:
同步方法时,由于同步监视器为this对象,所以可以直接调用这三个方法。
示例如下:
public class SyncMethodThreadCommunication { static class DataWrap{ int data = 0; boolean flag = false; public synchronized void addThreadA(){ if (flag) { try { wait(); } catch (InterruptedException e) { e.printStackTrace(); } } data++; System.out.println(Thread.currentThread().getName() + " " + data); flag = true; notify(); } public synchronized void addThreadB() { if (!flag) { try { wait(); } catch (InterruptedException e) { e.printStackTrace(); } } data++; System.out.println(Thread.currentThread().getName() + " " + data); flag = false; notify(); } } static class ThreadA extends Thread { private DataWrap data; public ThreadA(DataWrap dataWrap) { this.data = dataWrap; } @Override public void run() { for (int i = 0; i < 10; i++) { data.addThreadA(); } } } static class ThreadB extends Thread { private DataWrap data; public ThreadB(DataWrap dataWrap) { this.data = dataWrap; } @Override public void run() { for (int i = 0; i < 10; i++) { data.addThreadB(); } } } public static void main(String[] args) { //实现两个线程轮流对数据进行加一操作 DataWrap dataWrap = new DataWrap(); new ThreadA(dataWrap).start(); new ThreadB(dataWrap).start(); } }
同步代码块时,需要使用监视器对象调用这三个方法。
示例如下:
public class SyncBlockThreadComminication { static class DataWrap{ boolean flag; int data; } static class ThreadA extends Thread{ DataWrap dataWrap; public ThreadA(DataWrap dataWrap){ this.dataWrap = dataWrap; } @Override public void run() { for(int i = 0 ; i < 10; i++) { synchronized (dataWrap) { if (dataWrap.flag) { try { dataWrap.wait(); } catch (InterruptedException e) { e.printStackTrace(); } } dataWrap.data++; System.out.println(getName() + " " + dataWrap.data); dataWrap.flag = true; dataWrap.notify(); } } } } static class ThreadB extends Thread{ DataWrap dataWrap; public ThreadB(DataWrap dataWrap){ this.dataWrap = dataWrap; } @Override public void run() { for (int i = 0; i < 10; i++) { synchronized (dataWrap) { if (!dataWrap.flag) { try { dataWrap.wait(); } catch (InterruptedException e) { e.printStackTrace(); } } dataWrap.data++; System.out.println(getName() + " " + dataWrap.data); dataWrap.flag = false; dataWrap.notify(); } } } } public static void main(String[] args) { //实现两个线程轮流对数据进行加一操作 DataWrap dataWrap = new DataWrap(); new ThreadA(dataWrap).start(); new ThreadB(dataWrap).start(); } }
2、使用Condition控制线程通信
当使用Lock对象保证同步时,则使用Condition对象来保证协调。
示例如下:
import java.util.concurrent.locks.Condition; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock; import com.sun.media.sound.RIFFInvalidDataException; import javafx.scene.chart.PieChart.Data; public class SyncLockThreadCommunication { static class DataWrap { int data; boolean flag; private final Lock lock = new ReentrantLock(); private final Condition condition = lock.newCondition(); public void addThreadA() { lock.lock(); try { if (flag) { try { condition.await(); } catch (InterruptedException e) { e.printStackTrace(); } } data++; System.out.println(Thread.currentThread().getName() + " " + data); flag = true; condition.signal(); } finally { lock.unlock(); } } public void addThreadB() { lock.lock(); try { if (!flag) { try { condition.await(); } catch (InterruptedException e) { e.printStackTrace(); } } data++; System.out.println(Thread.currentThread().getName() + " " + data); flag = false; condition.signal(); } finally { lock.unlock(); } } } static class ThreadA extends Thread{ DataWrap dataWrap; public ThreadA(DataWrap dataWrap) { this.dataWrap = dataWrap; } @Override public void run() { for (int i = 0; i < 10; i++) { dataWrap.addThreadA(); } } } static class ThreadB extends Thread{ DataWrap dataWrap; public ThreadB(DataWrap dataWrap) { this.dataWrap = dataWrap; } @Override public void run() { for (int i = 0; i < 10; i++) { dataWrap.addThreadB(); } } } public static void main(String[] args) { //实现两个线程轮流对数据进行加一操作 DataWrap dataWrap = new DataWrap(); new ThreadA(dataWrap).start(); new ThreadB(dataWrap).start(); } }
其中Condition对象的await(), singal(),singalAll()分别对应wait(),notify()和notifyAll()方法。
3、使用阻塞队列BlockingQueue控制线程通信
BlockingQueue是Queue接口的子接口,主要用来做线程通信使用,它具有一个特征:当生产者线程试图向BlockingQueue中放入元素时,如果队列已满,则该线程被阻塞;当消费者线程试图从BlockingQueue中取出元素时,如果队列已空,则该线程被阻塞。这两个特征分别对应两个支持阻塞的方法,put(E e)和take()
示例如下:
import java.util.concurrent.ArrayBlockingQueue; import java.util.concurrent.BlockingQueue; public class BlockingQueueThreadComminication { static class DataWrap{ int data; } static class ThreadA extends Thread{ private BlockingQueue<DataWrap> blockingQueue; public ThreadA(BlockingQueue<DataWrap> blockingQueue, String name) { super(name); this.blockingQueue = blockingQueue; } @Override public void run() { for (int i = 0; i < 100; i++) { try { DataWrap dataWrap = blockingQueue.take(); dataWrap.data++; System.out.println(getName() + " " + dataWrap.data); sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } } } } static class ThreadB extends Thread{ private BlockingQueue<DataWrap> blockingQueue; private DataWrap dataWrap; public ThreadB(BlockingQueue<DataWrap> blockingQueue, DataWrap dataWrap, String name) { super(name); this.blockingQueue = blockingQueue; this.dataWrap = dataWrap; } @Override public void run() { for (int i = 0; i < 100; i++) { try { dataWrap.data++; System.out.println(getName() + " " + dataWrap.data); blockingQueue.put(dataWrap); sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } } } } public static void main(String[] args) { ///实现两个线程轮流对数据进行加一操作 DataWrap dataWrap = new DataWrap(); BlockingQueue<DataWrap> blockingQueue = new ArrayBlockingQueue<>(1); new ThreadA(blockingQueue, "Consumer").start(); new ThreadB(blockingQueue, dataWrap, "Producer").start(); } }
BlockingQueue共有五个实现类:
ArrayBlockingQueue 基于数组实现的BlockingQueue队列
LinkedBlockingQueue 基于链表实现的BlockingQueue队列
PriorityBlockingQueue 中元素需实现Comparable接口,其中元素的排序是按照Comparator进行的定制排序。
SynchronousQueue 同步队列,要求对该队列的存取操作必须是交替进行。
DelayQueue 集合元素必须实现Delay接口,队列中元素排序按照Delay接口方法getDelay()的返回值进行排序。