From ea49dd17eea804a2569531ea4cb8e1bd216717f7 Mon Sep 17 00:00:00 2001
From: Carl Hetherington <cth@carlh.net>
Date: Tue, 19 Jul 2016 21:09:12 +0100
Subject: [PATCH] Do parallel digest calculation when there are multiple reels
 (#855).

---
 src/lib/reel_writer.cc |  8 +++-----
 src/lib/reel_writer.h  |  4 ++--
 src/lib/writer.cc      | 46 +++++++++++++++++++++++++++++++++++++++---
 src/lib/writer.h       |  4 ++++
 4 files changed, 52 insertions(+), 10 deletions(-)

diff --git a/src/lib/reel_writer.cc b/src/lib/reel_writer.cc
index e6533d2cc..d576eb2a0 100644
--- a/src/lib/reel_writer.cc
+++ b/src/lib/reel_writer.cc
@@ -417,16 +417,14 @@ ReelWriter::create_reel (list<ReferencedReelAsset> const & refs, list<shared_ptr
 }
 
 void
-ReelWriter::calculate_digests (shared_ptr<Job> job)
+ReelWriter::calculate_digests (boost::function<void (float)> set_progress)
 {
-	job->sub (_("Computing image digest"));
 	if (_picture_asset) {
-		_picture_asset->hash (boost::bind (&Job::set_progress, job.get(), _1, false));
+		_picture_asset->hash (set_progress);
 	}
 
 	if (_sound_asset) {
-		job->sub (_("Computing audio digest"));
-		_sound_asset->hash (boost::bind (&Job::set_progress, job.get(), _1, false));
+		_sound_asset->hash (set_progress);
 	}
 }
 
diff --git a/src/lib/reel_writer.h b/src/lib/reel_writer.h
index 6e27171ec..9dc740171 100644
--- a/src/lib/reel_writer.h
+++ b/src/lib/reel_writer.h
@@ -1,5 +1,5 @@
 /*
-    Copyright (C) 2012-2015 Carl Hetherington <cth@carlh.net>
+    Copyright (C) 2012-2016 Carl Hetherington <cth@carlh.net>
 
     This file is part of DCP-o-matic.
 
@@ -57,7 +57,7 @@ public:
 
 	void finish ();
 	boost::shared_ptr<dcp::Reel> create_reel (std::list<ReferencedReelAsset> const & refs, std::list<boost::shared_ptr<Font> > const & fonts);
-	void calculate_digests (boost::shared_ptr<Job> job);
+	void calculate_digests (boost::function<void (float)> set_progress);
 
 	Frame start () const;
 
diff --git a/src/lib/writer.cc b/src/lib/writer.cc
index efd43a25b..1874e68f4 100644
--- a/src/lib/writer.cc
+++ b/src/lib/writer.cc
@@ -58,6 +58,9 @@ using std::pair;
 using std::string;
 using std::list;
 using std::cout;
+using std::map;
+using std::min;
+using std::max;
 using boost::shared_ptr;
 using boost::weak_ptr;
 using boost::dynamic_pointer_cast;
@@ -456,12 +459,34 @@ Writer::finish ()
 
 	dcp.add (cpl);
 
+	/* Calculate digests for each reel in parallel */
+
+	shared_ptr<Job> job = _job.lock ();
+	job->sub (_("Computing digests"));
+
+	boost::asio::io_service service;
+	boost::thread_group pool;
+
+	shared_ptr<boost::asio::io_service::work> work (new boost::asio::io_service::work (service));
+
+	int const threads = max (1, Config::instance()->num_local_encoding_threads ());
+
+	for (int i = 0; i < threads; ++i) {
+		pool.create_thread (boost::bind (&boost::asio::io_service::run, &service));
+	}
+
 	BOOST_FOREACH (ReelWriter& i, _reels) {
+		boost::function<void (float)> set_progress = boost::bind (&Writer::set_digest_progress, this, job.get(), _1);
+		service.post (boost::bind (&ReelWriter::calculate_digests, &i, set_progress));
+	}
 
-		shared_ptr<Job> job = _job.lock ();
-		DCPOMATIC_ASSERT (job);
-		i.calculate_digests (job);
+	work.reset ();
+	pool.join_all ();
+	service.stop ();
 
+	/* Add reels to CPL */
+
+	BOOST_FOREACH (ReelWriter& i, _reels) {
 		cpl->add (i.create_reel (_reel_assets, _fonts));
 	}
 
@@ -597,3 +622,18 @@ Writer::video_reel (int frame) const
 	DCPOMATIC_ASSERT (i < _reels.size ());
 	return i;
 }
+
+void
+Writer::set_digest_progress (Job* job, float progress)
+{
+	/* I believe this is thread-safe */
+	_digest_progresses[boost::this_thread::get_id()] = progress;
+
+	boost::mutex::scoped_lock lm (_digest_progresses_mutex);
+	float min_progress = 0;
+	for (map<boost::thread::id, float>::const_iterator i = _digest_progresses.begin(); i != _digest_progresses.end(); ++i) {
+		min_progress = min (min_progress, i->second);
+	}
+
+	job->set_progress (min_progress);
+}
diff --git a/src/lib/writer.h b/src/lib/writer.h
index 170307d8d..c1d7e4f8b 100644
--- a/src/lib/writer.h
+++ b/src/lib/writer.h
@@ -113,6 +113,7 @@ private:
 	void terminate_thread (bool);
 	bool have_sequenced_image_at_queue_head ();
 	size_t video_reel (int frame) const;
+	void set_digest_progress (Job* job, float progress);
 
 	/** our Film */
 	boost::shared_ptr<const Film> _film;
@@ -150,6 +151,9 @@ private:
 	*/
 	int _pushed_to_disk;
 
+	boost::mutex _digest_progresses_mutex;
+	std::map<boost::thread::id, float> _digest_progresses;
+
 	std::list<ReferencedReelAsset> _reel_assets;
 
 	std::list<boost::shared_ptr<Font> > _fonts;
-- 
2.30.2