一、Exchanger同步工具
可以在对中对元素进行配对和交换的线程的同步点。每个线程将条目上的某个方法呈现给 exchange
方法,与伙伴线程进行匹配,并且在返回时接收其伙伴的对象。Exchanger
可能被视为 SynchronousQueue
的双向形式。Exchanger
可能在应用程序(比如遗传算法和管道设计)中很有用。
1.1 API
API | 描述 |
---|---|
V exchange(V x) |
等待另一个线程到达此交换点(除非当前线程被中断),然后将给定的对象传送给该线程,并接收该线程的对象 |
V exchange(V x, long timeout, TimeUnit unit) |
等待另一个线程到达此交换点(除非当前线程被中断,或者超出了指定的等待时间),然后将给定的对象传送给该线程,同时接收该线程的对象。 |
1.2 用法分析
用法示例:以下是重点介绍的一个类,该类使用
Exchanger
在线程间交换缓冲区,因此,在需要时,填充缓冲区的线程获取一个新腾空的缓冲区,并将填满的缓冲区传递给腾空缓冲区的线程。(伪代码)
class FillAndEmpty {
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();
}
}
内存一致性效果:对于通过Exchanger
成功交换对象的每对线程,每个线程中在 exchange()
之前的操作 happen-before 从另一线程中相应的 exchange()
返回的后续操作。
1.3 案例分析
public class ExchangerTest {
public static void main(String[] args) {
ExecutorService service = Executors.newCachedThreadPool();
final Exchanger exchanger = new Exchanger();
service.execute(new Runnable(){
public void run() {
try {
String data1 = "zxx";
System.out.println("线程" + Thread.currentThread().getName() +
"正在把数据" + data1 +"换出去");
Thread.sleep((long)(Math.random()*10000));
String data2 = (String)exchanger.exchange(data1);
System.out.println("线程" + Thread.currentThread().getName() +
"换回的数据为" + data2);
}catch(Exception e){
}
}
});
service.execute(new Runnable(){
public void run() {
try {
String data1 = "lhm";
System.out.println("线程" + Thread.currentThread().getName() +
"正在把数据" + data1 +"换出去");
Thread.sleep((long)(Math.random()*10000));
String data2 = (String)exchanger.exchange(data1);
System.out.println("线程" + Thread.currentThread().getName() +
"换回的数据为" + data2);
}catch(Exception e){
}
}
});
}
}
打印结果
线程pool-1-thread-1正在把数据zxx换出去
线程pool-1-thread-2正在把数据lhm换出去
线程pool-1-thread-2换回的数据为zxx
线程pool-1-thread-1换回的数据为lhm
参考
张孝祥-Java多线程与并发库高级应用