java - 具有太多 Observable 的 RxJava1 StackOverflow 异常

Question

我正在使用 rxjava1 开发一个项目，我有一个 Observable 链，偶尔会包含数千个合并或连接在一起的 observable。当发生这种情况时，将发生 StackOverflow 异常，我们将得到如下信息:

java.lang.StackOverflowError
    at java.util.HashMap.putVal(HashMap.java:631)
    at java.util.HashMap.put(HashMap.java:612)
    at rx.internal.operators.OnSubscribeToMap$ToMapSubscriber.onNext(OnSubscribeToMap.java:127)
    at rx.internal.operators.OnSubscribeFilter$FilterSubscriber.onNext(OnSubscribeFilter.java:76)
    at rx.internal.operators.OperatorMerge$MergeSubscriber.emitScalar(OperatorMerge.java:395)
    at rx.internal.operators.OperatorMerge$MergeSubscriber.tryEmit(OperatorMerge.java:355)
    at rx.internal.operators.OperatorMerge$InnerSubscriber.onNext(OperatorMerge.java:846)
    at rx.internal.operators.OperatorMerge$MergeSubscriber.emitScalar(OperatorMerge.java:395)
    at rx.internal.operators.OperatorMerge$MergeSubscriber.tryEmit(OperatorMerge.java:355)
    at rx.internal.operators.OperatorMerge$InnerSubscriber.onNext(OperatorMerge.java:846)
    at rx.internal.operators.OperatorMerge$MergeSubscriber.emitScalar(OperatorMerge.java:395)
    at rx.internal.operators.OperatorMerge$MergeSubscriber.tryEmit(OperatorMerge.java:355)
    at rx.internal.operators.OperatorMerge$InnerSubscriber.onNext(OperatorMerge.java:846)
    at rx.internal.operators.OperatorMerge$MergeSubscriber.emitScalar(OperatorMerge.java:395)
    at rx.internal.operators.OperatorMerge$MergeSubscriber.tryEmit(OperatorMerge.java:355)
    at rx.internal.operators.OperatorMerge$InnerSubscriber.onNext(OperatorMerge.java:846)
    at rx.internal.operators.OperatorMerge$MergeSubscriber.emitScalar(OperatorMerge.java:395)
    at rx.internal.operators.OperatorMerge$MergeSubscriber.tryEmit(OperatorMerge.java:355)

堆栈跟踪将持续数百行。我看到的唯一相关帖子是 github 中的这个问题:https://github.com/ReactiveX/RxJava/issues/3035 .但是，将可观察对象添加到列表中的建议解决方案是我们已经使用过的，但行不通。

我能做些什么来防止这些 StackOverflow 异常？我是否需要进行某种节流或背压？

这是当前代码的样子并导致计算器溢出的示例:

public Observable<Map<String, JsonObject>> extractTopLevelSummariesFromForms(JsonArray summaries, Func2<String, String, Observable<JsonObject>> summaryGatherer) {
    List<Observable<JsonObject>> summaryObservables = new LinkedList<>();
    summaries.stream()
             .map(JsonUtil::safeJsonObject)
             .filter(summary -> StringUtils.isNotEmpty(summary.getString(NAME))|| StringUtils.isNotEmpty(summary.getString(Form.TITLE)))
             .forEach(summary -> {
                 if (StringUtils.isNotEmpty(summary.getString(TEXT)))
                     summaryObservables.add(gatherSummariesFromElement(summary.getString(Summary.SHORT_NAME), Summary.SummaryValues.FORM,
                                                                       summary.getString(Summary.SHORT_NAME) + ".hidden",
                                                                       summary.getString(VALUE), summaryGatherer));
                 if (StringUtils.isNotEmpty(summary.getString(Form.TEXT)))
                     summaryObservables.add(gatherSummariesFromElement(summary.getString(Summary.SHORT_NAME), Summary.SummaryValues.FORM,
                                                                       summary.getString(Summary.SHORT_NAME) + ".title",
                                                                       summary.getString(Summary.VALUE), summaryGatherer, true));
             });
    return Observable.merge(Observable.from(summaryObservables))
                     .filter(summaryResult -> summaryResult != null)
                     .toMap(summaryResult -> summaryResult.getString(KEY), summaryResult -> summaryResult.getJsonObject(TEXT));
}

 private Observable<JsonObject> gatherSummariesFromElement(String parentName, String parentType, String elementName, String summaryValue, Func2<String, String, Observable<JsonObject>> summaryGatherer, Set<String> visited, boolean isList) {
    if (visited.contains(elementName))
        return Observable.just(null);
    visited.add(elementName);

    Map<String, JsonObject> summariesMap = new HashMap<>();

    summariesMap.put(elementName, new JsonObject().put(Summary.SummaryValues.FORM, form).put(SUMMARY_TYPE, parentType));
    Set<String> variables = TextEngine.getVariables(summariesMap);

    Observable<JsonObject> elementSummaryObservable = Observable.just(getSummaryEntry(elementName, form, parentType, isList));

    if (variables != null && !variables.isEmpty()) {
        elementSummaryObservable = elementSummaryObservable.mergeWith(Observable.from(variables).flatMap(variable -> {
            if (StringUtils.contains(variable, ".") && StringUtils.equals(parentName, StringUtils.split(variable, ".")[0]))
                return Observable.just(null);
            else
                return summaryGatherer.call(parentName, variable).flatMap(variableEntry -> {
                    if (variableEntry == null)
                        return Observable.just(null);
                    else
                        return gatherSummariesFromElement(parentName, variableEntry.getString(SOURCE_TYPE), variable, variableEntry.getString(FORM), summaryGatherer, visited, variableEntry.getBoolean(Summary.SummaryValues.IS_LIST, false));
                });
        }));
    }
    return elementSummaryObservable;
}

我已经尝试在 Schedulers.computation() 调度程序中运行除网络请求之外的所有内容，那些在 Schedulers.io() 调度程序中运行，我是仍然得到计算器溢出:

Exception in thread "pool-26-thread-2" java.lang.IllegalStateException: Fatal Exception thrown on Scheduler.Worker thread.
at rx.internal.schedulers.ScheduledAction.run(ScheduledAction.java:59)
at rx.internal.schedulers.ExecutorScheduler$ExecutorSchedulerWorker.run(ExecutorScheduler.java:107)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.StackOverflowError
at rx.internal.operators.OperatorMerge$MergeSubscriber.tryEmit(OperatorMerge.java:355)
at rx.internal.operators.OperatorMerge$InnerSubscriber.onNext(OperatorMerge.java:846)
at rx.internal.operators.OperatorMerge$MergeSubscriber.emitScalar(OperatorMerge.java:395)
at rx.internal.operators.OperatorMerge$MergeSubscriber.tryEmit(OperatorMerge.java:355)
at rx.internal.operators.OperatorMerge$InnerSubscriber.onNext(OperatorMerge.java:846)
at rx.internal.operators.OperatorMerge$MergeSubscriber.emitScalar(OperatorMerge.java:395)

Answer 1

1. 您对 gatherSummariesFromElement 进行了递归调用，这可能会进行得非常深入
2. Observable.merge(Observable.from(summaryObservables)) 调用看起来很奇怪，你应该只使用 Observable.merge(summaryObservables)
3. 您可以使用 Observable.empty()
而不是使用 Observable.just(null) 然后过滤空值
4. summaryObservables 的构建看起来有点矫枉过正。您可以构建有效摘要列表而不是然后在 flatMap 中处理它们
5. 将 gatherSummariesFromElement 中的递归 Observable 创建替换为元素创建的递归列表，然后从该列表创建 observable

_

public Observable<Map<String, JsonObject>> extractTopLevelSummariesFromForms(JsonArray summaries, Func2<String, String, JsonObject> summaryGatherer) {
    List<JsonObject> validSummaries = new LinkedList<>();
    summaries.stream()
            .map(JsonUtil::safeJsonObject)
            .filter(summary -> StringUtils.isNotEmpty(summary.getString(NAME)) || StringUtils.isNotEmpty(summary.getString(Form.TITLE)))
            .forEach(validSummaries::add);
    Set<String> visited = new HashSet<>();
    return Observable.from(validSummaries)
            .flatMap(summary -> {
                if (StringUtils.isNotEmpty(summary.getString(TEXT)))
                    Observable.from(gatherSummariesFromElement(summary.getString(Summary.SHORT_NAME), Summary.SummaryValues.FORM,
                            summary.getString(Summary.SHORT_NAME) + ".hidden",
                            summary.getString(VALUE), visited, summaryGatherer)));
                if (StringUtils.isNotEmpty(summary.getString(Form.TEXT)))
                    Observable.from(gatherSummariesFromElement(summary.getString(Summary.SHORT_NAME), Summary.SummaryValues.FORM,
                            summary.getString(Summary.SHORT_NAME) + ".title",
                            summary.getString(Summary.VALUE), summaryGatherer, visited,true)));
            })
            .toMap(summaryResult -> summaryResult.getString(KEY), summaryResult -> summaryResult.getJsonObject(TEXT));
}

private List<JsonObject> gatherSummariesFromElement(String parentName, String parentType, String elementName, String summaryValue, Func2<String, String, JsonObject> summaryGatherer, Set<String> visited, boolean isList) {
    if (visited.contains(elementName))
        return Collections.emptyList();
    visited.add(elementName);
    List<JsonObject> result = new ArrayList<>()

    Map<String, JsonObject> summariesMap = new HashMap<>();

    summariesMap.put(elementName, new JsonObject().put(Summary.SummaryValues.FORM, form).put(SUMMARY_TYPE, parentType));
    Set<String> variables = TextEngine.getVariables(summariesMap);

    result.add(getSummaryEntry(elementName, form, parentType, isList));

    if (variables != null && !variables.isEmpty()) {
        for (String variable : variables) {
            if (StringUtils.contains(variable, ".") && StringUtils.equals(parentName, StringUtils.split(variable, ".")[0])) {
                // do nothing
            } else {
                JsonObject variableEntry = summaryGatherer.call(parentName, variable)
                if (variableEntry != null) {
                    result.addAll(gatherSummariesFromElement(parentName, variableEntry.getString(SOURCE_TYPE), variable, variableEntry.getString(FORM), summaryGatherer, visited, variableEntry.getBoolean(Summary.SummaryValues.IS_LIST, false));
                }
            }
        }
    }
    return result;
}