From ba123dfe878c8a37595a7855113fd0c91180209b Mon Sep 17 00:00:00 2001
From: Robin Gareus <robin@gareus.org>
Date: Wed, 6 Jan 2021 00:13:41 +0100
Subject: [PATCH] Cache playlist extents

Calculating the extents iterates over all regions which
can be expensive. Ardour's GUI calls this periodically to
calculate session_gui_extents().
---
 libs/ardour/ardour/playlist.h | 3 +++
 libs/ardour/playlist.cc       | 9 ++++++++-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/libs/ardour/ardour/playlist.h b/libs/ardour/ardour/playlist.h
index 75ab8b4f2f..bdf9788875 100644
--- a/libs/ardour/ardour/playlist.h
+++ b/libs/ardour/ardour/playlist.h
@@ -33,6 +33,7 @@
 #include <list>
 #include <boost/shared_ptr.hpp>
 #include <boost/enable_shared_from_this.hpp>
+#include <boost/optional.hpp>
 #include <boost/utility.hpp>
 
 #include <sys/stat.h>
@@ -432,6 +433,8 @@ private:
 	void coalesce_and_check_crossfades (std::list<Evoral::Range<samplepos_t> >);
 	boost::shared_ptr<RegionList> find_regions_at (samplepos_t);
 
+	mutable boost::optional<std::pair<samplepos_t, samplepos_t> > _cached_extent;
+
 	samplepos_t _end_space;  //this is used when we are pasting a range with extra space at the end
 	bool _playlist_shift_active;
 };
diff --git a/libs/ardour/playlist.cc b/libs/ardour/playlist.cc
index d9953e7e49..76676bd1cc 100644
--- a/libs/ardour/playlist.cc
+++ b/libs/ardour/playlist.cc
@@ -2238,6 +2238,8 @@ Playlist::find_next_region_boundary (samplepos_t sample, int dir)
 void
 Playlist::mark_session_dirty ()
 {
+	_cached_extent.reset ();
+
 	if (!in_set_state && !holding_state ()) {
 		_session.set_dirty();
 	}
@@ -2464,8 +2466,13 @@ Playlist::all_regions_empty() const
 pair<samplepos_t, samplepos_t>
 Playlist::get_extent () const
 {
+	if (_cached_extent) {
+		return _cached_extent.value ();
+	}
+
 	RegionReadLock rlock (const_cast<Playlist *>(this));
-	return _get_extent ();
+	_cached_extent = _get_extent ();
+	return _cached_extent.value ();
 }
 
 pair<samplepos_t, samplepos_t>