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ZEPPELIN-1420. java.util.ConcurrentModificationException caused by calling remove inside foreach loop #1419

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zjffdu wants to merge 1 commit into from
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ZEPPELIN-1420. java.util.ConcurrentModificationException caused by calling remove inside foreach loop #1419

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19 changes: 10 additions & 9 deletions zeppelin-zengine/src/main/java/org/apache/zeppelin/interpreter/InterpreterFactory.java
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Original file line number Diff line number Diff line change
Expand Up @@ -1017,15 +1017,16 @@ public List<String> getInterpreters(String noteId) {
public List<InterpreterSetting> getInterpreterSettings(String noteId) {
List<String> interpreterSettingIds = getNoteInterpreterSettingBinding(noteId);
LinkedList<InterpreterSetting> settings = new LinkedList<>();
synchronized (interpreterSettingIds) {
for (String id : interpreterSettingIds) {
InterpreterSetting setting = get(id);
if (setting == null) {
// interpreter setting is removed from factory. remove id from here, too
interpreterSettingIds.remove(id);
} else {
settings.add(setting);
}

Iterator<String> iter = interpreterSettingIds.iterator();
while (iter.hasNext()) {
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@zjffdu zjffdu Sep 9, 2016

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I also remove the synchronized block, it seems not necessary.

String id = iter.next();
InterpreterSetting setting = get(id);
if (setting == null) {
// interpreter setting is removed from factory. remove id from here, too
iter.remove();
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@prasadwagle prasadwagle Sep 9, 2016 •
edited
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What is the purpose of removing the id? It seems to me that interpreterSettingIds is a temporary LinkedList and the effect of removing id is not persisted.

  private List<String> getNoteInterpreterSettingBinding(String noteId) {
    LinkedList<String> bindings = new LinkedList<>();
    synchronized (interpreterSettings) {
      List<String> settingIds = interpreterBindings.get(noteId);
      if (settingIds != null) {
        bindings.addAll(settingIds);
      }
    }
    return bindings;
  }

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@zjffdu zjffdu Sep 12, 2016

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@prasadwagle It is because the interpreter setting may be removed in other threads, so we need to check it here. I don't quite understand your concern about the persistence.

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@echarles echarles Sep 12, 2016

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A few weeks ago, I came across the exact same question as @prasadwagle. Call remote on the temporary (not returned) list is useless (this consideration/question is separate from this PR which aims solving the concurrent modification exception (which I met also), but is worth to consider).

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@khalidhuseynov khalidhuseynov Sep 18, 2016

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that's good question although not related to topic of this PR. maybe @jongyoul could bring little clarity as I believe he's the original author of that function

} else {
settings.add(setting);
}
}
return settings;
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