westonpace commented on a change in pull request #12662:
URL: https://github.com/apache/arrow/pull/12662#discussion_r832732700
##########
File path: cpp/src/arrow/util/async_generator.h
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@@ -60,6 +60,9 @@ namespace arrow {
// Readahead operators, and some other operators, may introduce queueing. Any
operators
// that introduce buffering should detail the amount of buffering they
introduce in their
// MakeXYZ function comments.
+//
+// A generator should always be fully consumed before it is destroyed.
+// A generator should not emit a terminal item until it has finished all
ongoing futures.
Review comment:
I ended up with:
```
// A generator should not mark a future complete with an error status or a
terminal value
// until all outstanding futures have completed. Generators that spawn
multiple
// concurrent futures may need to hold onto an error while other
concurrent futures wrap
// up.
```
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