Java 线程通信

时间:2021-05-31 14:30:38

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。