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分享java 多线程实现生产者模型问题
public class Baskert {
private List<String> list = new ArrayList<String>();
private Lock lock = new ReentrantLock();
private Condition setter = lock.newCondition(); //篮子为满的条件
private Condition getter = lock.newCondition(); //篮子为空的条件
public void addApple() throws InterruptedException{
try{
lock.lock();
while(list.size()>=5){
System.out.println(Thread.currentThread().getName()+"--挂起");
setter.await();
}
list.add("红富士");
System.out.println(Thread.currentThread().getName()+"放了一个红富士==="+list.size());
System.out.println("释放2,3");
getter.signalAll();
}finally{
lock.unlock();
}
}
public void removeApple() throws InterruptedException{
try{
lock.lock();
while(list.size()<=0){
System.out.println(Thread.currentThread().getName()+"--挂起");
getter.await();
}
list.remove(0);
System.out.println(Thread.currentThread().getName()+"拿了一个苹果==="+list.size());
System.out.println("释放0,1");
setter.signalAll();
}finally{
lock.unlock();
}
}
public static void main(String[] args){
final Baskert baskert = new Baskert();
new Thread(new Runnable() {
public void run() {
try {
while(true){
baskert.addApple();
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}).start();
new Thread(new Runnable() {
public void run() {
try {
while(true){
baskert.addApple();
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}).start();
new Thread(new Runnable() {
public void run() {
try {
while(true){
baskert.removeApple();
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}).start();
new Thread(new Runnable() {
public void run() {
try {
while(true){
baskert.removeApple();
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}).start();
}
}
结果是：
Thread-1放了一个红富士===1
释放2,3
Thread-1放了一个红富士===2
释放2,3
Thread-1放了一个红富士===3
释放2,3
Thread-1放了一个红富士===4
释放2,3
Thread-1放了一个红富士===5
释放2,3
Thread-1--挂起
Thread-0--挂起
Thread-3拿了一个苹果===4
释放0,1
Thread-3拿了一个苹果===3
释放0,1
Thread-3拿了一个苹果===2
释放0,1
Thread-3拿了一个苹果===1
释放0,1
Thread-3拿了一个苹果===0
释放0,1
Thread-3--挂起
Thread-2--挂起
Thread-1放了一个红富士===1
释放2,3
Thread-1放了一个红富士===2
可见只有一个线程把篮子放满或者拿空，挂起之后另一个线程才会操作。
而我觉得结果应该是 只要篮子不满或者不空，放苹果线程和取苹果线程应该是同时进行的，请高手指点为什么会这样
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流氓T-T兔 2014-01-09
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数量 50 100，500 结果都一样
流氓T-T兔 2014-01-09
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谢谢
不过你的输出结果和预期相同，是不是因为你waitRandomTime方法调用了sleep。为什么不用sleep执行顺序就不对，巧合吗
remember1989 2014-01-09
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之前那个有问题，因为控制台的输出并不是严格按照先后顺序来的，所以不能依赖控制台输出来观察多线程的运行，必须先按照先后顺序把消息记下来，然后再一把输出。
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Random;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* 多线程生产者-消费者示例
*/
public class Basket {
public static final int BASKET_CAPACITY = 5;
private List<String> list = new ArrayList<>();
private Lock lock = new ReentrantLock();
private Condition setter = lock.newCondition(); //篮子为满的条件
private Condition getter = lock.newCondition(); //篮子为空的条件
// 放入苹果
public void addApple() throws InterruptedException {
try {
lock.lock();
while (list.size() >= BASKET_CAPACITY) {
addMessage("+++ 篮子已满，等待取出");
setter.await();
}
list.add("红富士");
addMessage("+++ 放入苹果: 篮子里还有" + list.size());
getter.signalAll();
} finally {
lock.unlock();
}
}
// 取出苹果
public void removeApple() throws InterruptedException {
try {
lock.lock();
while (list.size() <= 0) {
addMessage("--- 篮子已空，等待放入");
getter.await();
}
list.remove(0);
addMessage("--- 取出苹果: 篮子里还有" + list.size());
setter.signalAll();
} finally {
lock.unlock();
}
}
/////////////////////////////////////////////////////////
public static void main(String[] args) throws Exception {
final Basket baskert = new Basket();
// 通过调整 AddAppleTask 和 RemoveAppleTask 的线程数，可以
// 观察篮子满或空的情况
startTask(new AddAppleTask(baskert));
startTask(new AddAppleTask(baskert));
startTask(new AddAppleTask(baskert));
startTask(new RemoveAppleTask(baskert));
startTask(new RemoveAppleTask(baskert));
System.out.println("线程运行中，请等待 10 秒...");
Thread.sleep(10000); // 让线程运行 10 秒钟
stop = true;
Thread.sleep(2000); // 等待所有线程停止
outputMessagesWithOrder(); // 按照次序打印消息
}
private static void startTask(Runnable runnable) {
Thread thread = new Thread(runnable);
thread.setDaemon(true);
thread.start();
}
/////////////////////////////////////////////////////////
/**
* 放入苹果线程
*/
private static class AddAppleTask implements Runnable {
private final Basket basket;
public AddAppleTask(Basket basket) {
this.basket = basket;
}
public void run() {
try {
while (waitRandomTime()) {
basket.addApple();
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
/**
* 取出苹果线程
*/
private static class RemoveAppleTask implements Runnable {
private final Basket basket;
public RemoveAppleTask(Basket basket) {
this.basket = basket;
}
public void run() {
try {
while (waitRandomTime()) {
basket.removeApple();
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
/////////////////////////////////////////////////////////
public static final Random RANDOM = new Random();
private static boolean stop = false;
private static List<String> messages = new ArrayList<>();
private static final AtomicInteger serial = new AtomicInteger();
private static synchronized void addMessage(String message) {
messages.add(String.format("%4d[%8s] %s",
serial.incrementAndGet(), Thread.currentThread().getName(), message));
}
private static void outputMessagesWithOrder() {
Collections.sort(messages);
for (String message : messages) {
System.out.println(message);
}
}
private static boolean waitRandomTime() {
try {
Thread.sleep(RANDOM.nextInt(1000) + 500);
} catch (InterruptedException e) {
e.printStackTrace();
}
return !stop;
}
}
骑士的崛起 2014-01-09
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你代码没问题，把苹果数量调大可以出现你要的结果。
remember1989 2014-01-09
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你的代码没有问题，我重新组织了一下，以便更好地观察结果。
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* 多线程生产者-消费者示例
*/
public class Basket {
public static final int BASKET_CAPACITY = 5;
private List<String> list = new ArrayList<>();
private Lock lock = new ReentrantLock();
private Condition setter = lock.newCondition(); //篮子为满的条件
private Condition getter = lock.newCondition(); //篮子为空的条件
// 放入苹果
public void addApple() throws InterruptedException {
try {
lock.lock();
while (list.size() >= BASKET_CAPACITY) {
outputThreadMessage("篮子已满，等待取出", false);
setter.await();
}
list.add("红富士");
outputThreadMessage("放入苹果: 篮子里还有" + list.size(), false);
getter.signalAll();
} finally {
lock.unlock();
}
}
// 取出苹果
public void removeApple() throws InterruptedException {
try {
lock.lock();
while (list.size() <= 0) {
outputThreadMessage("篮子已空，等待放入", true);
getter.await();
}
list.remove(0);
outputThreadMessage("取出苹果: 篮子里还有" + list.size(), true);
setter.signalAll();
} finally {
lock.unlock();
}
}
public static void main(String[] args) {
final Basket baskert = new Basket();
// 通过调整 AddAppleTask 和 RemoveAppleTask 的线程数，可以
// 观察篮子满或空的情况
new Thread(new AddAppleTask(baskert)).start();
new Thread(new AddAppleTask(baskert)).start();
new Thread(new RemoveAppleTask(baskert)).start();
new Thread(new RemoveAppleTask(baskert)).start();
}
/**
* 放入苹果线程
*/
private static class AddAppleTask implements Runnable {
private final Basket basket;
public AddAppleTask(Basket basket) {
this.basket = basket;
}
public void run() {
try {
while (waitRandomTime()) {
basket.addApple();
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
/**
* 取出苹果线程
*/
private static class RemoveAppleTask implements Runnable {
private final Basket basket;
public RemoveAppleTask(Basket basket) {
this.basket = basket;
}
public void run() {
try {
while (waitRandomTime()) {
basket.removeApple();
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
/////////////////////////////////////////////////////////
public static final Random RANDOM = new Random();
private static void outputThreadMessage(String message, boolean err) {
if (err) {
System.err.printf("[%10s] %s\n", Thread.currentThread().getName(), message);
} else {
System.out.printf("[%10s] %s\n", Thread.currentThread().getName(), message);
}
}
private static boolean waitRandomTime() {
try {
Thread.sleep(RANDOM.nextInt(1000) + 500);
return true;
} catch (InterruptedException e) {
e.printStackTrace();
return false;
}
}
}
骑士的崛起 2014-01-09
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数量 50 100，500 结果都一样[/quote]
你代码耗时太低了，应该是计算线程优先级的问题，我这里调到30就能出现你想要的结果，加上Thread.sleep(1000)调到20就能出现你要的结果。
