From 25674c1e6a66715286f7f9a5116fdf3baff1c738 Mon Sep 17 00:00:00 2001
From: Carl Hetherington <cth@carlh.net>
Date: Mon, 30 Dec 2013 21:46:10 +0000
Subject: [PATCH] Comment and slightly tidy ExceptionStore.

---
 src/lib/encoder.cc   |  4 +---
 src/lib/exceptions.h | 25 +++++++++++++++++++------
 src/lib/writer.cc    |  4 +---
 3 files changed, 21 insertions(+), 12 deletions(-)

diff --git a/src/lib/encoder.cc b/src/lib/encoder.cc
index eff38b6a5..ca75e4ca1 100644
--- a/src/lib/encoder.cc
+++ b/src/lib/encoder.cc
@@ -199,9 +199,7 @@ Encoder::process_video (shared_ptr<PlayerImage> image, Eyes eyes, ColourConversi
 		return;
 	}
 
-	if (_writer->thrown ()) {
-		_writer->rethrow ();
-	}
+	_writer->rethrow ();
 
 	if (_writer->can_fake_write (_video_frames_out)) {
 		_writer->fake_write (_video_frames_out, eyes);
diff --git a/src/lib/exceptions.h b/src/lib/exceptions.h
index f4631c09b..c1240538f 100644
--- a/src/lib/exceptions.h
+++ b/src/lib/exceptions.h
@@ -230,17 +230,30 @@ public:
 	PixelFormatError (std::string o, AVPixelFormat f);
 };
 
+/** A parent class for classes which have a need to catch and
+ *  re-throw exceptions.  This is intended for classes
+ *  which run their own thread; they should do something like
+ *
+ *  void my_thread ()
+ *  try {
+ *    // do things which might throw exceptions
+ *  } catch (...) {
+ *    store_current ();
+ *  }
+ *
+ *  and then in another thread call rethrow().  If any
+ *  exception was thrown by my_thread it will be stored by
+ *  store_current() and then rethrow() will re-throw it where
+ *  it can be handled.
+ */
 class ExceptionStore
 {
 public:
-	bool thrown () const {
-		boost::mutex::scoped_lock lm (_mutex);
-		return _exception;
-	}
-	
 	void rethrow () {
 		boost::mutex::scoped_lock lm (_mutex);
-		boost::rethrow_exception (_exception);
+		if (_exception) {
+			boost::rethrow_exception (_exception);
+		}
 	}
 
 protected:	
diff --git a/src/lib/writer.cc b/src/lib/writer.cc
index 4129b7a82..414ea72eb 100644
--- a/src/lib/writer.cc
+++ b/src/lib/writer.cc
@@ -335,9 +335,7 @@ Writer::finish ()
 	lock.unlock ();
 
 	_thread->join ();
-	if (thrown ()) {
-		rethrow ();
-	}
+	rethrow ();
 	
 	delete _thread;
 	_thread = 0;
-- 
2.30.2