rtpsw commented on code in PR #34311:
URL: https://github.com/apache/arrow/pull/34311#discussion_r1116168128
##########
cpp/src/arrow/compute/exec/aggregate_node.cc:
##########
@@ -43,7 +44,45 @@ namespace compute {
namespace {
-namespace {
+/// \brief A gated shared mutex is similar to a shared mutex, in that it
allows either
+/// multiple shared readers or a unique writer access to the mutex, except
that a waiting
+/// writer gates future readers by preventing them from reacquiring shared
access until it
+/// has acquired and released the mutex. This is useful for ensuring a writer
is never
+/// starved by readers.
+struct GatedSharedMutex {
+ std::mutex gate;
+ std::shared_mutex mutex;
+};
+
+/// \brief Acquires unique access to a gatex mutex. This is useful for a
unique writer.
+class GatedUniqueLock {
+ public:
+ // acquires the gate first, to ensure future readers will wait for its
release
+ explicit GatedUniqueLock(GatedSharedMutex& gated_shared_mutex)
+ : lock_gate_(gated_shared_mutex.gate),
lock_mutex_(gated_shared_mutex.mutex) {}
+
+ private:
+ std::unique_lock<std::mutex> lock_gate_;
+ std::unique_lock<std::shared_mutex> lock_mutex_;
+};
+
+/// \brief Acquires shared access to a gatex mutex. This is useful for a
shared reader.
+class GatedSharedLock {
Review Comment:
It's from [an earlier phase of working on this
PR](https://github.com/apache/arrow/pull/14352#issuecomment-1279750410) and is
only needed for multi-threaded segmented aggregation, which we decided not to
support for now, so it can (and will) be removed.
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