From 73ebb92e9df01ba7afb97121b6e2cef6ca13a18e Mon Sep 17 00:00:00 2001
From: Carl Hetherington <cth@carlh.net>
Date: Thu, 23 Jul 2020 22:53:43 +0200
Subject: [PATCH] Use thread_group for improved exception safety (#1785).

---
 src/lib/encode_server.cc | 14 ++++--------
 src/lib/encode_server.h  |  2 +-
 src/lib/j2k_encoder.cc   | 46 +++++++++++++++-------------------------
 src/lib/j2k_encoder.h    |  5 ++---
 4 files changed, 24 insertions(+), 43 deletions(-)

diff --git a/src/lib/encode_server.cc b/src/lib/encode_server.cc
index 8db3f867c..c242cb216 100644
--- a/src/lib/encode_server.cc
+++ b/src/lib/encode_server.cc
@@ -87,14 +87,9 @@ EncodeServer::~EncodeServer ()
 		_full_condition.notify_all ();
 	}
 
-	BOOST_FOREACH (boost::thread* i, _worker_threads) {
-		try {
-			i->join ();
-		} catch (...) {
-
-		}
-		delete i;
-	}
+	try {
+		_worker_threads.join_all ();
+	} catch (...) {}
 
 	{
 		boost::mutex::scoped_lock lm (_broadcast.mutex);
@@ -241,8 +236,7 @@ EncodeServer::run ()
 	}
 
 	for (int i = 0; i < _num_threads; ++i) {
-		boost::thread* t = new thread(bind(&EncodeServer::worker_thread, this));
-		_worker_threads.push_back (t);
+		boost::thread* t = _worker_threads.create_thread (bind(&EncodeServer::worker_thread, this));
 #ifdef DCPOMATIC_LINUX
 		pthread_setname_np (t->native_handle(), "encode-server-worker");
 #endif
diff --git a/src/lib/encode_server.h b/src/lib/encode_server.h
index 91e007503..a43cea7ef 100644
--- a/src/lib/encode_server.h
+++ b/src/lib/encode_server.h
@@ -54,7 +54,7 @@ private:
 	void broadcast_thread ();
 	void broadcast_received ();
 
-	std::vector<boost::thread*> _worker_threads;
+	boost::thread_group _worker_threads;
 	std::list<boost::shared_ptr<Socket> > _queue;
 	boost::condition _full_condition;
 	boost::condition _empty_condition;
diff --git a/src/lib/j2k_encoder.cc b/src/lib/j2k_encoder.cc
index 3d7b342da..498050073 100644
--- a/src/lib/j2k_encoder.cc
+++ b/src/lib/j2k_encoder.cc
@@ -185,11 +185,7 @@ J2KEncoder::encode (shared_ptr<PlayerVideo> pv, DCPTime time)
 {
 	_waker.nudge ();
 
-	size_t threads = 0;
-	{
-		boost::mutex::scoped_lock threads_lock (_threads_mutex);
-		threads = _threads.size ();
-	}
+	size_t threads = _threads->size();
 
 	boost::mutex::scoped_lock queue_lock (_queue_mutex);
 
@@ -250,26 +246,20 @@ J2KEncoder::encode (shared_ptr<PlayerVideo> pv, DCPTime time)
 void
 J2KEncoder::terminate_threads ()
 {
-	boost::mutex::scoped_lock threads_lock (_threads_mutex);
+	if (!_threads) {
+		return;
+	}
 
-	int n = 0;
-	BOOST_FOREACH (boost::thread* i, _threads) {
-		/* Be careful not to throw in here otherwise _threads will not be clear()ed */
-		LOG_GENERAL ("Terminating thread %1 of %2", n + 1, _threads.size ());
-		i->interrupt ();
-		try {
-			i->join ();
-		} catch (exception& e) {
-			LOG_ERROR ("join() threw an exception: %1", e.what());
-		} catch (...) {
-			LOG_ERROR_NC ("join() threw an exception");
-		}
-		LOG_GENERAL_NC ("Thread terminated");
-		++n;
-		delete i;
+	_threads->interrupt_all ();
+	try {
+		_threads->join_all ();
+	} catch (exception& e) {
+		LOG_ERROR ("join() threw an exception: %1", e.what());
+	} catch (...) {
+		LOG_ERROR_NC ("join() threw an exception");
 	}
 
-	_threads.clear ();
+	_threads.reset ();
 }
 
 void
@@ -383,11 +373,10 @@ void
 J2KEncoder::servers_list_changed ()
 {
 	terminate_threads ();
+	_threads.reset (new boost::thread_group());
 
 	/* XXX: could re-use threads */
 
-	boost::mutex::scoped_lock lm (_threads_mutex);
-
 #ifdef BOOST_THREAD_PLATFORM_WIN32
 	OSVERSIONINFO info;
 	info.dwOSVersionInfoSize = sizeof (OSVERSIONINFO);
@@ -400,12 +389,11 @@ J2KEncoder::servers_list_changed ()
 
 	if (!Config::instance()->only_servers_encode ()) {
 		for (int i = 0; i < Config::instance()->master_encoding_threads (); ++i) {
-			boost::thread* t = new boost::thread (boost::bind(&J2KEncoder::encoder_thread, this, optional<EncodeServerDescription>()));
+			boost::thread* t = _threads->create_thread(boost::bind(&J2KEncoder::encoder_thread, this, optional<EncodeServerDescription>()));
 #ifdef DCPOMATIC_LINUX
 			pthread_setname_np (t->native_handle(), "encode-worker");
 #endif
-			_threads.push_back (t);
-#ifdef BOOST_THREAD_PLATFORM_WIN32
+#ifdef DCPOMATIC_WINDOWS
 			if (windows_xp) {
 				SetThreadAffinityMask (t->native_handle(), 1 << i);
 			}
@@ -420,9 +408,9 @@ J2KEncoder::servers_list_changed ()
 
 		LOG_GENERAL (N_("Adding %1 worker threads for remote %2"), i.threads(), i.host_name ());
 		for (int j = 0; j < i.threads(); ++j) {
-			_threads.push_back (new boost::thread(boost::bind(&J2KEncoder::encoder_thread, this, i)));
+			_threads->create_thread(boost::bind(&J2KEncoder::encoder_thread, this, i));
 		}
 	}
 
-	_writer->set_encoder_threads (_threads.size ());
+	_writer->set_encoder_threads (_threads->size());
 }
diff --git a/src/lib/j2k_encoder.h b/src/lib/j2k_encoder.h
index b4542c40a..d56fc1aec 100644
--- a/src/lib/j2k_encoder.h
+++ b/src/lib/j2k_encoder.h
@@ -87,9 +87,8 @@ private:
 
 	EventHistory _history;
 
-	/** Mutex for _threads */
-	mutable boost::mutex _threads_mutex;
-	std::list<boost::thread*> _threads;
+	boost::shared_ptr<boost::thread_group> _threads;
+
 	mutable boost::mutex _queue_mutex;
 	std::list<boost::shared_ptr<DCPVideo> > _queue;
 	/** condition to manage thread wakeups when we have nothing to do */
-- 
2.30.2