westonpace commented on a change in pull request #11285:
URL: https://github.com/apache/arrow/pull/11285#discussion_r723662097
##########
File path: cpp/src/arrow/dataset/scanner.h
##########
@@ -123,6 +123,12 @@ struct ARROW_DS_EXPORT ScanOptions {
/// Fragment-specific scan options.
std::shared_ptr<FragmentScanOptions> fragment_scan_options;
+ /// Callback which will be run whenever the scanner pauses due to
backpressure
+ ///
+ /// This is mostly for debugging & tracing so that the consumer can be
notified if
+ /// they are not consuming data quickly enough.
+ std::function<void()> on_paused_callback;
Review comment:
Oops, I left this in. That was an earlier attempt at fixing the test >_<
##########
File path: cpp/src/arrow/util/thread_pool.h
##########
@@ -341,6 +341,9 @@ class ARROW_EXPORT ThreadPool : public Executor {
// tasks are finished.
Status Shutdown(bool wait = true);
+
+ void WaitForIdle();
Review comment:
Yes, I will document that. ThreadPool is internal (and I'm not
proposing we add WaitForIdle to Executor) so I hope that is reasonable. CC
@pitrou for thoughts. For context: I added `WaitForIdle` to the `ThreadPool`
purely for the sake of sequencing some testing.
##########
File path: cpp/src/arrow/dataset/scanner.h
##########
@@ -123,6 +123,12 @@ struct ARROW_DS_EXPORT ScanOptions {
/// Fragment-specific scan options.
std::shared_ptr<FragmentScanOptions> fragment_scan_options;
+ /// Callback which will be run whenever the scanner pauses due to
backpressure
+ ///
+ /// This is mostly for debugging & tracing so that the consumer can be
notified if
+ /// they are not consuming data quickly enough.
+ std::function<void()> on_paused_callback;
Review comment:
I've removed this and did some general cleanup of the PR.
##########
File path: cpp/src/arrow/dataset/scanner_test.cc
##########
@@ -1025,13 +1035,20 @@ TEST_F(TestBackpressure, ScanBatchesUnordered) {
EXPECT_OK_AND_ASSIGN(AsyncGenerator<EnumeratedRecordBatch> gen,
scanner->ScanBatchesUnorderedAsync());
ASSERT_FINISHES_OK(gen());
+ // Wait for the thread pool to idle. By this point the scanner should have
paused itself
+ // This helps with timing on slower CI systems where there is only one core
and the scanner
+ // might keep that core until it has scanned all the batches which never
gives the sink a
+ // chance to report it is falling behind.
+ GetCpuThreadPool()->WaitForIdle();
+ DeliverAdditionalBatches();
// The exact numbers may be imprecise due to threading but we should pretty
quickly read
// up to our backpressure limit and a little above. We should not be able
to go too far
// above.
- BusyWait(10, [&] { return TotalBatchesRead() >= kDefaultBackpressureHigh; });
+ ASSERT_TRUE(TotalBatchesRead() >= kDefaultBackpressureHigh);
Review comment:
Fixed.
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