lidavidm commented on a change in pull request #11207:
URL: https://github.com/apache/arrow/pull/11207#discussion_r714322177
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File path: cpp/src/arrow/util/async_generator.h
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@@ -221,6 +221,9 @@ class MappingGenerator {
bool should_trigger;
{
auto guard = state->mutex.Lock();
+ // A MappedCallback may have purged or be purging the queue;
+ // we shouldn't do anything here.
+ if (state->finished) return;
Review comment:
That test case uses an overload of MakeMappedGenerator which doesn't
exist in the fork (it takes a bool as the third argument) - what was the
purpose there?
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File path: cpp/src/arrow/util/async_generator.h
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@@ -1001,32 +1004,45 @@ class MergedGenerator {
};
struct InnerCallback {
Review comment:
Yup, that's it. And in particular the degenerate case here is that the
synchronously-run callback from the mapped generator's futures would pull from
the mapped generator, creating a loop implemented as (non-tail) recursion.
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