Reactive Streams：一种支持背压的异步数据流处理标准，主流实现有RxJava和Reactor，Spring WebFlux默认集成的是Reacto
Reactive Streams：一种支持背压的异步数据流处理标准，主流实现有RxJava和Reactor，Spring WebFlux默认集成的是Reactor。
Reactive Streams主要解决背压(back-pressure)问题。当传入的任务速率大于系统处理能力时，数据处理将会对未处理数据产生一个缓冲区。
背压依我的理解来说，是指订阅者能和发布者交互(通过代码里面的调用request和cancel方法交互)，可以调节发布者发布数据的速率，解决把订阅者压垮的问题。关键在于上面例子里面的订阅关系Subscription这个接口，他有request和cancel 2个方法，用于通知发布者需要数据和通知发布者不再接受数据。
我们重点理解背压在jdk9里面是如何实现的。关键在于发布者Publisher的实现类SubmissionPublisher的submit方法是block方法。订阅者会有一个缓冲池，默认为Flow.defaultBufferSize() = 256。当订阅者的缓冲池满了之后，发布者调用submit方法发布数据就会被阻塞，发布者就会停(慢)下来；订阅者消费了数据之后(调用Subscription.request方法)，缓冲池有位置了，submit方法就会继续执行下去，就是通过这样的机制，实现了调节发布者发布数据的速率，消费得快，生成就快，消费得慢，发布者就会被阻塞，当然就会慢下来了。
单线程版本：
一个生产者，一个消费者
import lombok.SneakyThrows;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
public class BackpressureExample {
public static void main(String[] args) throws InterruptedException {
BackpressureSubscriber subscriber = new BackpressureSubscriber();
BackpressurePublisher publisher = new BackpressurePublisher(subscriber);
publisher.start();
subscriber.start();
// 为了演示效果，这里让主线程休眠一段时间
Thread.sleep(50000);
publisher.stop();
subscriber.stop();
}
@SneakyThrows
public static void processDataLogic(List<Integer> batch) {
//模拟任务执行
int r = new Random().nextInt(3000);
Thread.sleep(r);
System.out.println(Thread.currentThread().getName() + ",Received batch: " + batch + ",sleep ms = " + r);
}
static class BackpressurePublisher {
private final BackpressureSubscriber subscriber;
private volatile boolean running;
public BackpressurePublisher(BackpressureSubscriber subscriber) {
this.subscriber = subscriber;
this.running = true;
}
public void start() {
Thread thread = new Thread(() -> {
int item = 1;
while (running) {
List<Integer> batch = new ArrayList<>();
for (int i = 0; i < 5; i++) {
System.out.println(Thread.currentThread().getName() + "-----produce data = " + item);
batch.add(item++);
}
while (!subscriber.accept(batch)) {
if (!running) {
break;
}
}
}
});
thread.start();
}
public void stop() {
running = false;
}
}
static class BackpressureSubscriber {
private volatile boolean running;
public BackpressureSubscriber() {
this.running = true;
}
public boolean accept(List<Integer> batch) {
if (running) {
processDataLogic(batch);
return true;
} else {
return false;
}
}
public void start() {
// Subscriber 在 JDK 8 中没有异步处理的能力，因此不需要单独开启线程
}
public void stop() {
running = false;
}
}
}多线程版本
一个生产者，多个消费者
import lombok.SneakyThrows;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
public class BackpressureExample {
public static void main(String[] args) throws InterruptedException {
BackpressureSubscriber subscriber = new BackpressureSubscriber();
BackpressurePublisher publisher = new BackpressurePublisher(subscriber);
publisher.start();
subscriber.start();
// 为了演示效果，这里让主线程休眠一段时间
Thread.sleep(50000);
publisher.stop();
subscriber.stop();
}
@SneakyThrows
public static void processDataLogic(List<Integer> batch) {
//模拟任务执行
int r = new Random().nextInt(3000);
Thread.sleep(r);
System.out.println(Thread.currentThread().getName() + ",Received batch: " + batch + ",sleep ms = " + r);
}
static class BackpressurePublisher {
private final BackpressureSubscriber subscriber;
private volatile boolean running;
public BackpressurePublisher(BackpressureSubscriber subscriber) {
this.subscriber = subscriber;
this.running = true;
}
public void start() {
Thread thread = new Thread(() -> {
int item = 1;
while (running) {
List<Integer> batch = new ArrayList<>();
for (int i = 0; i < 5; i++) {
System.out.println(Thread.currentThread().getName() + "-----produce data = " + item);
batch.add(item++);
}
while (!subscriber.accept(batch)) {
if (!running) {
break;
}
}
}
});
thread.start();
}
public void stop() {
running = false;
}
}
static class BackpressureSubscriber {
private volatile boolean running;
private final ExecutorService executor;
private final int workerSize = 2;
private final List<Future> futures;
public BackpressureSubscriber() {
this.running = true;
this.executor = Executors.newFixedThreadPool(workerSize);
futures = new ArrayList<>(workerSize);
}
public boolean accept(List<Integer> batch) {
if (running) {
Future f = executor.submit(() -> processDataLogic(batch));
futures.add(f);
waitForTaskDone(futures);
return true;
} else {
return false;
}
}
public void waitForTaskDone(List<Future> futures) {
while (futures.size() >= workerSize) {
for (Future future : futures) {
if (future.isDone()) {
// 只要有一个worker是空闲就重新获取任务
futures.remove(future);
return;
}
}
}
}
public void start() {
// Subscriber 在 JDK 8 中没有异步处理的能力，因此不需要单独开启线程
}
public void stop() {
running = false;
executor.shutdown();
}
}
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