Question

我正在尝试定期发出事件（每150ms），即使上游的observable会更快地发送事件。

但即使我已拨打MissingBackpressureException

，我也会收到onBackpressureBlock()

代码：

    SerializedSubject<QuotationMarker, QuotationMarker> subject = new SerializedSubject<> (PublishSubject.create());

    return subject
            .subscribeOn(Schedulers.computation())
            .doOnSubscribe(() -> {
                NetworkRequestsManager.instance().queryQuotations(productId).subscribe(quotation -> {
                            Log.d(TAG, "new quotation " + quotation.hashCode());
                            NetworkRequestsManager.instance().getSeller(quotation.sellerId)
                                    .subscribe(seller -> {
                                                for (Outlet outlet : seller.outlets) {
                                                    if (outlet.latitude != null && outlet.longitude != null)
                                                        subject.onNext(new QuotationMarker(outlet, quotation.price));
                                                }
                                            },
                                            error -> Log.fatalError(new RuntimeException(error)));
                        },
                        error -> Log.fatalError(new RuntimeException(error)));

            })
            .doOnError(throwable -> Log.fatalError(new RuntimeException(
                    "error response in subscribe after doOnSubscribe",
                    throwable)))
                    // combine with another observable that emits items regularly (every 100ms)
                    // so that a new event is received every 100ms :
                    // also, first event itself is delayed.
            .zipWith(Observable.interval(150, TimeUnit.MILLISECONDS),
                    (seller, aLong) -> seller)
            .onBackpressureBlock() // prevent zipWith Observer.interval from throwing MissingBackpressureException s
            .doOnError(throwable -> Log.fatalError(new RuntimeException(
                    "error response after onBackpressureBlock()",
                    throwable))); // <-- error is thrown here

迹：

    05-06 00:38:25.532  28106-28166/com.instano.buyer W/System.err﹕ java.lang.RuntimeException: error response after onBackpressureBlock()
    05-06 00:38:25.572  28106-28166/com.instano.buyer W/System.err﹕ at com.instano.retailer.instano.application.controller.Quotations.lambda$fetchQuotationMarkersForProduct$59(Quotations.java:67)
    05-06 00:38:25.572  28106-28166/com.instano.buyer W/System.err﹕ at com.instano.retailer.instano.application.controller.Quotations.access$lambda$5(Quotations.java)
    05-06 00:38:25.572  28106-28166/com.instano.buyer W/System.err﹕ at com.instano.retailer.instano.application.controller.Quotations$$Lambda$8.call(Unknown Source)
    05-06 00:38:25.572  28106-28166/com.instano.buyer W/System.err﹕ at rx.Observable$11.onError(Observable.java:4193)
    05-06 00:38:25.572  28106-28166/com.instano.buyer W/System.err﹕ at rx.internal.operators.OperatorDoOnEach$1.onError(OperatorDoOnEach.java:65)
    05-06 00:38:25.572  28106-28166/com.instano.buyer W/System.err﹕ at rx.internal.operators.OperatorOnBackpressureBlock$BlockingSubscriber.complete(OperatorOnBackpressureBlock.java:81)
    05-06 00:38:25.572  28106-28166/com.instano.buyer W/System.err﹕ at rx.internal.util.BackpressureDrainManager.drain(BackpressureDrainManager.java:190)
    05-06 00:38:25.572  28106-28166/com.instano.buyer W/System.err﹕ at rx.internal.util.BackpressureDrainManager.terminateAndDrain(BackpressureDrainManager.java:129)
    05-06 00:38:25.572  28106-28166/com.instano.buyer W/System.err﹕ at rx.internal.operators.OperatorOnBackpressureBlock$BlockingSubscriber.onError(OperatorOnBackpressureBlock.java:68)
    05-06 00:38:25.572  28106-28166/com.instano.buyer W/System.err﹕ at rx.internal.operators.OperatorZip$Zip$InnerSubscriber.onError(OperatorZip.java:324)
    05-06 00:38:25.572  28106-28166/com.instano.buyer W/System.err﹕ at rx.internal.operators.OperatorZip$Zip$InnerSubscriber.onNext(OperatorZip.java:332)
    05-06 00:38:25.572  28106-28166/com.instano.buyer W/System.err﹕ at rx.internal.operators.OnSubscribeTimerPeriodically$1.call(OnSubscribeTimerPeriodically.java:51)
    05-06 00:38:25.572  28106-28166/com.instano.buyer W/System.err﹕ at rx.Scheduler$Worker$1.call(Scheduler.java:120)
    05-06 00:38:25.572  28106-28166/com.instano.buyer W/System.err﹕ at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:55)
    05-06 00:38:25.572  28106-28166/com.instano.buyer W/System.err﹕ at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:390)
    05-06 00:38:25.572  28106-28166/com.instano.buyer W/System.err﹕ at java.util.concurrent.FutureTask.run(FutureTask.java:234)
    05-06 00:38:25.582  28106-28166/com.instano.buyer W/System.err﹕ at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:153)
    05-06 00:38:25.592  28106-28166/com.instano.buyer W/System.err﹕ at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:267)
    05-06 00:38:25.602  28106-28166/com.instano.buyer W/System.err﹕ at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
    05-06 00:38:25.602  28106-28166/com.instano.buyer W/System.err﹕ at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
    05-06 00:38:25.602  28106-28166/com.instano.buyer W/System.err﹕ at java.lang.Thread.run(Thread.java:841)
    05-06 00:38:25.602  28106-28166/com.instano.buyer W/System.err﹕ Caused by: rx.exceptions.MissingBackpressureException
    05-06 00:38:25.612  28106-28166/com.instano.buyer W/System.err﹕ at rx.internal.util.RxRingBuffer.onNext(RxRingBuffer.java:349)
    05-06 00:38:25.642  28106-28166/com.instano.buyer W/System.err﹕ at rx.internal.operators.OperatorZip$Zip$InnerSubscriber.onNext(OperatorZip.java:330)
    05-06 00:38:25.642  28106-28166/com.instano.buyer W/System.err﹕ ... 10 more

PS：Log.fatalError(err)只是Android.util.Log.e(...)

的封套

修改

经过大量的反复试验，这对我来说变成了wont fix。 zipWith(Observable.interval...)似乎是罪魁祸首和可能的框架错误。删除这些行（以及我的周期性发射功能）我的代码可以工作。我正在使用一个可能从不同线程调用onNext的主题，然后我在它上面执行Obeservable运算符。

Answer 1

我认为（但我不确定）问题是您的背压配置是在zip运算符之后。

zip运算符需要缓冲一个Observable的项目以将其与另一个Observable压缩。这是应该抛出异常的缓冲区。（见here）

要解决您的问题，我认为您应该尝试在Observable运算符中使用的zip上添加背压配置。

示例：

obs.zipWith(Observable.interval(150, TimeUnit.MILLISECONDS).onBackPressureDrop());

obs.onBackPressureBlock().zipWith(Observable.interval(150, TimeUnit.MILLISECONDS));

Answer 2

@dwursteisen和@zsxwing的答案是正确的。

区间运算符是基于时间发出的运算符，因此是＆＃34; hot＆＃34;并且不支持背压。因此，它将继续发出并填充zip的内部有界缓冲区，从而导致MissingBackpressureException。

处理＆＃34; hot＆＃34;源（例如基于时间或用户事件的源）必须选择如何处理溢出的策略。

在这种情况下，您需要将该策略放在interval运算符上。

以下代码显示了正在进行的操作以及处理它的选项：

import java.util.concurrent.TimeUnit;

import rx.Observable;


public class ZipInterval {

    public static void main(String... args) {
        Observable<Long> slowHotSource = Observable.interval(1, TimeUnit.SECONDS);

        /** This one is fast and hot so will cause a MissingBackpressureException.
         *  
         * This is because a "hot" source based on time does not obey backpressure
         * and keeps emitting regardless of what the downstream asks for.
         * 
         * Examples of "hot" and "cold" and approaches to both can be found at:
         * https://speakerdeck.com/benjchristensen/reactive-programming-with-rx-at-qconsf-2014?slide=90 and
         * https://github.com/ReactiveX/RxJava/wiki/Backpressure
         * */ 
        // Observable<Long> fastHotSource = Observable.interval(1, TimeUnit.MILLISECONDS);

        /**
         * The following version of 'fastHotSource' composes a simple flow control strategy.
         */
        Observable<Long> fastHotSource = Observable.interval(1, TimeUnit.MILLISECONDS).onBackpressureDrop();

        Observable<String> zipped = Observable.zip(slowHotSource, fastHotSource, (s, f) -> {
            return s + " " + f;
        });

        // subscribe to the output
        System.out.println("---- zip output");
        zipped.take(10).toBlocking().forEach(System.out::println);

        /**
         * The outcome of the above is probably not what is expected though. 
         * 
         * This is because zip will buffer the output and then `fastHotSource` will drop until
         * the zip buffer asks for more.
         * 
         * For temporal or "hot" sources like this, using `withLatestFrom` or `combineLatest`
         * is often more appropriate than `zip`.
         */

        Observable<String> latest = slowHotSource.withLatestFrom(fastHotSource, (s, f) -> {
            return s + " " + f;
        });

        // subscribe to the output
        System.out.println("---- latest output");
        latest.take(10).toBlocking().forEach(System.out::println);
    }
}

这个输出是：

---- zip output
0 0
1 1
2 2
3 3
4 4
5 5
6 6
7 7
8 8
9 9
---- latest output
0 1002
1 2002
2 3000
3 4001
4 5003
5 6001
6 7000
7 8002
8 9005
9 10000

Answer 3

尝试使用combineLatest，因为组合lastest不会等待新值调用onNext，它会在新值到达函数时使用最新值

调用onBackpressureBlock（）后甚至出现MissingBackpressureException

3 个答案: