Method ~SerialIterator

cpp/src/arrow/util/thread_pool.h:327–344

      ARROW_DISALLOW_COPY_AND_ASSIGN(SerialIterator);
      ARROW_DEFAULT_MOVE_AND_ASSIGN(SerialIterator);
      ~SerialIterator() {
        // A serial iterator must be consumed before it can be destroyed.  Allowing it to
        // do otherwise would lead to resource leakage.  There will likely be deadlocks at
        // this spot in the future but these will be the result of other bugs and not the
        // fact that we are forcing consumption here.

        // If a streaming API needs to support early abandonment then it should be done so
        // with a cancellation token and not simply discarding the iterator and expecting
        // the underlying work to clean up correctly.
        if (executor && !executor->IsFinished()) {
          while (true) {
            Result<T> maybe_next = Next();
            if (!maybe_next.ok() || IsIterationEnd(*maybe_next)) {
              break;
            }
          }
        }
      }

      Result<T> Next() {
        executor->Unpause();