具有太多可观察量的RxJava1 StackOverflow异常

时间：2018-06-08 04:22:57

标签： java exception rx-java stack-overflow

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

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。我见过的唯一相关帖子是github中的这个问题：https://github.com/ReactiveX/RxJava/issues/3035。但是建议的将可观察量添加到列表中的解决方案是我们已经使用过但不起作用的。

如何防止这些StackOverflow异常？我需要做某种节流或背压吗？

以下是当前代码的示例以及导致stackoverflows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，这些请求正在Schedulers.io()调度程序中运行，我仍然得到堆栈溢出：

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)

1 个答案:

答案 0 :(得分：4)

  1. 你有gatherSummariesFromElement的递归调用，这可能会非常深入
  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.just(null)
    4. ，而不是使用Observable.empty()然后过滤空值
  4. 构建summaryObservables看起来有点矫枉过正。您可以构建有效摘要列表，而不是在flatMap
    5. 中处理它们
  5. 使用递归的元素创建列表替换gatherSummariesFromElement中的递归Observable创建，然后从该列表创建observable

    6. _ 

    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;
}
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