SwitchIfEmpty链导致StackOverflowError。

huangapple
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英文:

SwitchIfEmpty Chain results in StackOverflowError

问题

以下代码会导致 StackOverflowError。在编写类似这样的代码时，这是否应该发生，还是说这是框架中需要解决的问题？

该代码已在 rxjava-2.2.19 中进行了测试。代码源可以在此处找到。

示例

以下代码基于我们用来实现某种带有中断条件的循环的代码（参见 flowable = flowable.switchIfEmpty(third(s))）。显然，这种方法并不奏效。

  1. public class SwitchIfEmptyTest {
  3.     public static void main(String[] args) {
  4.         SwitchIfEmptyDemo demo = new SwitchIfEmptyDemo();
  5.         demo.one("foo")
  6.             .blockingForEach(s -> System.out.println(s));
  7.     }
  9.     static class SwitchIfEmptyDemo {
  11.         private SomeSource source = new SomeSource();
  13.         public Flowable<String> one(String input) {
  14.             return Flowable.<String>empty()
  15.                 .switchIfEmpty(two(input));
  16.         }
  18.         public Flowable<String> two(String input) {
  19.             return Flowable.<String>create(emitter -> {
  20.                 emitter.onNext(input);
  21.                 emitter.onComplete();
  22.             }, BackpressureStrategy.ERROR)
  23.                 .flatMap(inputFlowable -> {
  24.                     return source.read()
  25.                         .toList()
  26.                         .toFlowable()
  27.                         .flatMap(strings -> {
  28.                             Flowable<String> flowable = Flowable.empty();
  29.                             for (String s : strings) {
  30.                                 flowable = flowable.switchIfEmpty(third(s));
  31.                             }
  32.                             return flowable;
  33.                         });
  34.                 });
  35.         }
  37.         public Flowable<String> third(String input) {
  38.             //System.out.println("Value " + input);
  39.             return Flowable.empty();
  40.         }
  41.     }
  43.     static class SomeSource {
  45.         public Flowable<String> read() {
  46.             return Flowable.create(emitter -> {
  47.                 for (int i = 0; i < 1_000_000; i++) {
  48.                     emitter.onNext("Some values " + i);
  49.                 }
  50.                 emitter.onComplete();
  51.             }, BackpressureStrategy.ERROR);
  52.         }
  53.     }
  54. }

堆栈跟踪

  1. Exception in thread "main" java.lang.StackOverflowError
  2.     at java.lang.ClassLoader.defineClass1(Native Method)
  3.     at java.lang.ClassLoader.defineClass(ClassLoader.java:756)
  4.     at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
  5.     at java.net.URLClassLoader.defineClass(URLClassLoader.java:468)
  6.     at java.net.URLClassLoader.access$100(URLClassLoader.java:74)
  7.     at java.net.URLClassLoader$1.run(URLClassLoader.java:369)
  8.     at java.net.URLClassLoader$1.run(URLClassLoader.java:363)
  9.     at java.security.AccessController.doPrivileged(Native Method)
  10.     at java.net.URLClassLoader.findClass(URLClassLoader.java:362)
  11.     at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
  12.     at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:352)
  13.     at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
  14.     at io.reactivex.Flowable.subscribe(Flowable.java:14939)
  15.     at io.reactivex.internal.operators.flowable.FlowableSwitchIfEmpty.subscribeActual(FlowableSwitchIfEmpty.java:32)
  16.     at io.reactivex.Flowable.subscribe(Flowable.java:14935)
  17.     at io.reactivex.internal.operators.flowable.FlowableSwitchIfEmpty.subscribeActual(FlowableSwitchIfEmpty.java:32)
  18.     at io.reactivex.Flowable.subscribe(Flowable.java:14935)
  19.     at io.reactivex.internal.operators.flowable.FlowableSwitchIfEmpty.subscribeActual(FlowableSwitchIfEmpty.java:32)
  20.     ...
英文:

The following code results in a StackOverflowError. Is this supposed to happen when writing code like this or is it something that needs to be addressed in the framework?

The code has been tested with rxjava-2.2.19. Sources can be found here.

Sample

The following code is based on code we use to accomplish some sort of looping with a break condition (see flowable = flowable.switchIfEmpty(third(s))). Apparently this approach is not working quite well.

  1. public class SwitchIfEmptyTest {
  2. public static void main(String[] args) {
  3. SwitchIfEmptyDemo demo = new SwitchIfEmptyDemo();
  4. demo.one(&quot;foo&quot;)
  5. .blockingForEach(s -&gt; System.out.println(s));
  6. }
  7. static class SwitchIfEmptyDemo {
  8. private SomeSource source = new SomeSource();
  9. public Flowable&lt;String&gt; one(String input) {
  10. return Flowable.&lt;String&gt;empty()
  11. .switchIfEmpty(two(input));
  12. }
  13. public Flowable&lt;String&gt; two(String input) {
  14. return Flowable.&lt;String&gt;create(emitter -&gt; {
  15. emitter.onNext(input);
  16. emitter.onComplete();
  17. }, BackpressureStrategy.ERROR)
  18. .flatMap(inputFlowable -&gt; {
  19. return source.read()
  20. .toList()
  21. .toFlowable()
  22. .flatMap(strings -&gt; {
  23. Flowable&lt;String&gt; flowable = Flowable.empty();
  24. for (String s : strings) {
  25. flowable = flowable.switchIfEmpty(third(s));
  26. }
  27. return flowable;
  28. });
  29. });
  30. }
  31. public Flowable&lt;String&gt; third(String input) {
  32. //System.out.println(&quot;Value &quot; + input);
  33. return Flowable.empty();
  34. }
  35. }
  36. static class SomeSource {
  37. public Flowable&lt;String&gt; read() {
  38. return Flowable.create(emitter -&gt; {
  39. for (int i = 0; i &lt; 1_000_000; i++) {
  40. emitter.onNext(&quot;Some values &quot; + i);
  41. }
  42. emitter.onComplete();
  43. }, BackpressureStrategy.ERROR);
  44. }
  45. }
  46. }

Stacktrace

  1. Exception in thread &quot;main&quot; java.lang.StackOverflowError
  2. at java.lang.ClassLoader.defineClass1(Native Method)
  3. at java.lang.ClassLoader.defineClass(ClassLoader.java:756)
  4. at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
  5. at java.net.URLClassLoader.defineClass(URLClassLoader.java:468)
  6. at java.net.URLClassLoader.access$100(URLClassLoader.java:74)
  7. at java.net.URLClassLoader$1.run(URLClassLoader.java:369)
  8. at java.net.URLClassLoader$1.run(URLClassLoader.java:363)
  9. at java.security.AccessController.doPrivileged(Native Method)
  10. at java.net.URLClassLoader.findClass(URLClassLoader.java:362)
  11. at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
  12. at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:352)
  13. at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
  14. at io.reactivex.Flowable.subscribe(Flowable.java:14939)
  15. at io.reactivex.internal.operators.flowable.FlowableSwitchIfEmpty.subscribeActual(FlowableSwitchIfEmpty.java:32)
  16. at io.reactivex.Flowable.subscribe(Flowable.java:14935)
  17. at io.reactivex.internal.operators.flowable.FlowableSwitchIfEmpty.subscribeActual(FlowableSwitchIfEmpty.java:32)
  18. at io.reactivex.Flowable.subscribe(Flowable.java:14935)
  19. at io.reactivex.internal.operators.flowable.FlowableSwitchIfEmpty.subscribeActual(FlowableSwitchIfEmpty.java:32)
  20. ...

答案1

得分: 0

以下是翻译好的内容：

为了消除 StackOverflowError，一种可能性是使用 takeWhile 操作符（详见完整差异）。

<!-- language: lang-java -->

  1. public Flowable<String> two(String input) {
  2.     return Flowable.<String>create(emitter -> {
  3.         emitter.onNext(input);
  4.         emitter.onComplete();
  5.     }, BackpressureStrategy.ERROR)
  6.     .flatMap(inputFlowable -> {
  7.         return source.read()
  8.             .flatMap(this::third)
  9.             .takeWhile(s -> s.equals("false"));
  10.     });
  11. }
英文:

In order to get rid of the StackOverflowError, one possibility is to use the takeWhile operator (see full diff).

<!-- language: lang-java -->

  1. public Flowable&lt;String&gt; two(String input) {
  2. return Flowable.&lt;String&gt;create(emitter -&gt; {
  3. emitter.onNext(input);
  4. emitter.onComplete();
  5. }, BackpressureStrategy.ERROR)
  6. .flatMap(inputFlowable -&gt; {
  7. return source.read()
  8. .flatMap(this::third)
  9. .takeWhile(s -&gt; s.equals(&quot;false&quot;));
  10. });
  11. }

huangapple
  • 本文由 发表于 2020年8月20日 00:08:37
  • 转载请务必保留本文链接：https://go.coder-hub.com/63490987.html
  • java
  • rx-java
  • rx-java2
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