From 0a9f5423f5b3faede68fe7c384c5fe32db2e23bf Mon Sep 17 00:00:00 2001
From: Paul Davis <paul@linuxaudiosystems.com>
Date: Sun, 29 May 2011 17:35:21 +0000
Subject: detect buffer "overflow" when delivering immediate events and queue
 remainder for delivery next time (though without actually requeing - just
 leave ringbuffer ptrs/indexes where they are. required some deep but minor
 changes in how MidiRingBuffer::read() works, so that we can detect if we're
 going to be able to deliver an event before we actually read any of its data.
 Peek FTW!

git-svn-id: svn://localhost/ardour2/branches/3.0@9629 d708f5d6-7413-0410-9779-e7cbd77b26cf
---
 libs/ardour/midi_ring_buffer.cc | 58 +++++++++++++++++++++++++++--------------
 1 file changed, 39 insertions(+), 19 deletions(-)

(limited to 'libs/ardour/midi_ring_buffer.cc')

diff --git a/libs/ardour/midi_ring_buffer.cc b/libs/ardour/midi_ring_buffer.cc
index 850313cc12..824d3bad84 100644
--- a/libs/ardour/midi_ring_buffer.cc
+++ b/libs/ardour/midi_ring_buffer.cc
@@ -34,7 +34,7 @@ using namespace PBD;
  */
 template<typename T>
 size_t
-MidiRingBuffer<T>::read(MidiBuffer& dst, framepos_t start, framepos_t end, framecnt_t offset)
+MidiRingBuffer<T>::read(MidiBuffer& dst, framepos_t start, framepos_t end, framecnt_t offset, bool stop_on_overflow_in_dst)
 {
 	if (this->read_space() == 0) {
 		return 0;
@@ -74,9 +74,22 @@ MidiRingBuffer<T>::read(MidiBuffer& dst, framepos_t start, framepos_t end, frame
 
 	size_t count = 0;
 
-	while (this->read_space() >= sizeof(T) + sizeof(Evoral::EventType) + sizeof(uint32_t)) {
+	const size_t prefix_size = sizeof(T) + sizeof(Evoral::EventType) + sizeof(uint32_t);
 
-		this->peek ((uint8_t*) &ev_time, sizeof (T));
+	while (this->read_space() >= prefix_size) {
+
+		uint8_t peekbuf[prefix_size];
+		bool success;
+
+		success = this->peek (peekbuf, prefix_size);
+		/* this cannot fail, because we've already verified that there
+		   is prefix_space to read
+		*/
+		assert (success);
+
+		ev_time = *((T*) peekbuf);
+		ev_type = *((Evoral::EventType*)(peekbuf + sizeof (T)));
+		ev_size = *((uint32_t*)(peekbuf + sizeof(T) + sizeof (Evoral::EventType)));
 
 		if (ev_time + loop_offset >= end) {
 			DEBUG_TRACE (DEBUG::MidiDiskstreamIO, string_compose ("MRB event @ %1 past end @ %2\n", ev_time, end));
@@ -87,13 +100,33 @@ MidiRingBuffer<T>::read(MidiBuffer& dst, framepos_t start, framepos_t end, frame
 		} else {
 			DEBUG_TRACE (DEBUG::MidiDiskstreamIO, string_compose ("MRB event @ %1 in range %2 .. %3\n", ev_time, start, end));
 		}
+		
+		/* lets see if we are going to be able to write this event into dst.
+		 */
+
+		assert(ev_time >= start);
+		
+		ev_time -= start;
+		ev_time += offset;
 
-		bool success = read_prefix(&ev_time, &ev_type, &ev_size);
-		if (!success) {
-			cerr << "WARNING: error reading event prefix from MIDI ring" << endl;
+		// write the timestamp to address (write_loc - 1)
+		uint8_t* write_loc = dst.reserve(ev_time, ev_size);
+		if (write_loc == NULL) {
+			if (stop_on_overflow_in_dst) {
+				DEBUG_TRACE (DEBUG::MidiDiskstreamIO, string_compose ("MidiRingBuffer: overflow in destination MIDI buffer, stopped after %1 events\n", count));
+				break;
+			}
+			cerr << "MRB: Unable to reserve space in buffer, event skipped";
+			this->increment_read_ptr (prefix_size + ev_size); // Advance read pointer to next event
 			continue;
 		}
 
+		/* we're good to go ahead and read the data now but since we
+		 * have the prefix data already, just skip over that
+		 */
+
+		this->increment_read_ptr (prefix_size);
+
 		// This event marks a loop end (i.e. the next event's timestamp will be non-monotonic)
 		if (ev_type == LoopEventType) {
 			assert (ev_size == sizeof (framepos_t));
@@ -120,19 +153,6 @@ MidiRingBuffer<T>::read(MidiBuffer& dst, framepos_t start, framepos_t end, frame
 			}
 		}
 
-		assert(ev_time >= start);
-		
-		ev_time -= start;
-		ev_time += offset;
-
-		// write the timestamp to address (write_loc - 1)
-		uint8_t* write_loc = dst.reserve(ev_time, ev_size);
-		if (write_loc == NULL) {
-			cerr << "MRB: Unable to reserve space in buffer, event skipped";
-			this->increment_read_ptr (ev_size); // Advance read pointer to next event
-			continue;
-		}
-
 		// write MIDI buffer contents
 		success = read_contents (ev_size, write_loc);
 
-- 
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