文章目錄
-
- 1 Exchanger 是什麼
- 2 Exchanger 詳解
- 3 Exchanger 應用
JDK 1.5 開始 JUC 包下提供的 Exchanger 類可用于兩個線程之間交換資訊。Exchanger 對象可了解為一個包含2個格子的容器,通過調用 exchanger 方法向其中的格子填充資訊,當兩個格子中的均被填充資訊時,自動交換兩個格子中的資訊,然後将交換的資訊傳回給調用線程,進而實作兩個線程的資訊交換。
功能看似簡單,但這在某些場景下是很有用處的,例如遊戲中兩個玩家交換裝備;交友軟體男女心儀對象比對。
下面簡單模拟下兩個玩家交換裝備的場景。
package com.chenpi;
import java.util.concurrent.Exchanger;
/**
* @Description
* @Author 陳皮
* @Date 2021/7/11
* @Version 1.0
*/
public class ChenPiMain {
public static void main(String[] args) throws InterruptedException {
Exchanger<String> exchanger = new Exchanger<>();
new Thread(() -> {
String str = null;
try {
str = exchanger.exchange("屠龍刀");
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("交易成功," + Thread.currentThread().getName() + "獲得" + str);
}, "周芷若").start();
new Thread(() -> {
String str = null;
try {
str = exchanger.exchange("倚天劍");
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("交易成功," + Thread.currentThread().getName() + "獲得" + str);
}, "張無忌").start();
}
}
// 輸出結果如下
交易成功,張無忌獲得屠龍刀
交易成功,周芷若獲得倚天劍
Exchager 類可用于兩個線程之間交換資訊,如果一個線程調用了 Exchanger 對象的 exchange 方法之後,會一直阻塞直到另一個線程來和它交換資訊,交換之後的資訊傳回給調用線程,進而實作兩個線程的資訊交換。
Exchager 底層也是使用到了自旋和 cas 機制。
注意,如果超過兩個線程調用同一個 Exchanger 對象 exchange 方法時,結果是不可預計的,隻要有2個線程滿足條件了,就認為比對成功并交換資訊。而剩下的未能得到配對的線程,則會被阻塞一直等待直到有另一個線程能與它比對與之配對。
package com.chenpi;
import java.util.concurrent.Exchanger;
/**
* @Description
* @Author 陳皮
* @Date 2021/7/11
* @Version 1.0
*/
public class ChenPiMain {
public static void main(String[] args) {
Exchanger<String> exchanger = new Exchanger<>();
new Thread(() -> {
String str = null;
try {
str = exchanger.exchange("屠龍刀");
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("交易成功," + Thread.currentThread().getName() + "獲得" + str);
}, "周芷若").start();
new Thread(() -> {
String str = null;
try {
str = exchanger.exchange("倚天劍");
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("交易成功," + Thread.currentThread().getName() + "獲得" + str);
}, "張無忌").start();
new Thread(() -> {
String str = null;
try {
str = exchanger.exchange("假的倚天劍");
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("交易成功," + Thread.currentThread().getName() + "獲得" + str);
}, "成昆").start();
}
}
// 輸出結果如下
交易成功,周芷若獲得假的倚天劍
交易成功,成昆獲得屠龍刀
當然,在等待交換資訊的線程是可以被中斷的,就比如玩家在等待交易過程中,突然玩家下線了,那就應該中斷線程等待。
package com.chenpi;
import java.lang.Thread.State;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Exchanger;
/**
* @Description
* @Author 陳皮
* @Date 2021/7/11
* @Version 1.0
*/
public class ChenPiMain {
public static void main(String[] args) throws InterruptedException {
Exchanger<String> exchanger = new Exchanger<>();
List<Thread> threads = new ArrayList<>(3);
Thread thread1 = new Thread(() -> {
String str = null;
try {
str = exchanger.exchange("屠龍刀");
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("交易成功," + Thread.currentThread().getName() + "獲得" + str);
}, "周芷若");
threads.add(thread1);
Thread thread2 = new Thread(() -> {
String str = null;
try {
str = exchanger.exchange("倚天劍");
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("交易成功," + Thread.currentThread().getName() + "獲得" + str);
}, "張無忌");
threads.add(thread2);
Thread thread3 = new Thread(() -> {
String str = null;
try {
str = exchanger.exchange("假的屠龍刀");
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("交易成功," + Thread.currentThread().getName() + "獲得" + str);
}, "成昆");
threads.add(thread3);
for (Thread thread : threads) {
thread.start();
}
// 等待5秒
Thread.sleep(5000);
for (Thread thread : threads) {
System.out.println(thread.getName() + ":" + thread.getState());
// 如果還在阻塞等待則中斷線程
if (thread.getState() == State.WAITING) {
thread.interrupt();
}
}
}
}
// 輸出結果如下
交易成功,張無忌獲得屠龍刀
交易成功,周芷若獲得倚天劍
周芷若:TERMINATED
張無忌:TERMINATED
成昆:WAITING
交易成功,成昆獲得null
java.lang.InterruptedException
at java.util.concurrent.Exchanger.exchange(Exchanger.java:568)
at com.chenpi.ChenPiMain.lambda$main$2(ChenPiMain.java:47)
at java.lang.Thread.run(Thread.java:748)
上面示範的是線程如果等不到另一個線程和它交換資訊,則會一直等待下去。其實 Exchanger 還可以設定等待指定時間。比如系統設定玩家交換裝備比對時間為60秒,如果超出時間則終止交易。
package com.chenpi;
import java.util.concurrent.Exchanger;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
/**
* @Description
* @Author 陳皮
* @Date 2021/7/11
* @Version 1.0
*/
public class ChenPiMain {
public static void main(String[] args) {
Exchanger<String> exchanger = new Exchanger<>();
new Thread(() -> {
try {
// 逾時時間設定為5秒
String str = exchanger.exchange("屠龍刀", 5, TimeUnit.SECONDS);
System.out.println("交易成功," + Thread.currentThread().getName() + "獲得" + str);
} catch (TimeoutException e) {
System.out.println("交易逾時!");
e.printStackTrace();
} catch (InterruptedException e) {
System.out.println("交易異常終止");
e.printStackTrace();
}
}, "周芷若").start();
}
}
// 輸出結果如下
交易逾時!
java.util.concurrent.TimeoutException
at java.util.concurrent.Exchanger.exchange(Exchanger.java:626)
at com.chenpi.ChenPiMain.lambda$main$0(ChenPiMain.java:22)
at java.lang.Thread.run(Thread.java:748)
package com.chenpi;
import java.awt.image.DataBuffer;
import java.util.concurrent.Exchanger;
/**
* @Description
* @Author 陳皮
* @Date 2021/7/11
* @Version 1.0
*/
public class ChenPiMain {
Exchanger<DataBuffer> exchanger = new Exchanger<DataBuffer>();
DataBuffer initialEmptyBuffer = ... a made-up type
DataBuffer initialFullBuffer = ...
class FillingLoop implements Runnable {
public void run() {
DataBuffer currentBuffer = initialEmptyBuffer;
try {
while (currentBuffer != null) {
addToBuffer(currentBuffer);
if (currentBuffer.isFull()) {
currentBuffer = exchanger.exchange(currentBuffer);
}
}
} catch (InterruptedException ex) { ...handle ...}
}
}
class EmptyingLoop implements Runnable {
public void run() {
DataBuffer currentBuffer = initialFullBuffer;
try {
while (currentBuffer != null) {
takeFromBuffer(currentBuffer);
if (currentBuffer.isEmpty()) {
currentBuffer = exchanger.exchange(currentBuffer);
}
}
} catch (InterruptedException ex) { ...handle ...}
}
}
void start() {
new Thread(new FillingLoop()).start();
new Thread(new EmptyingLoop()).start();
}
}