core: add a spsc ringbuffer implementation

Currently every single AO was implementing it's own ringbuffer, many times
with slightly different semantics. This is an attempt to fix the problem.

I stole some good ideas from ao_portaudio's ringbuffer and went from there.
The main difference is this one stores wpos and rpos which are absolute
positions in an "infinite" buffer. To find the actual position for writing /
reading just apply modulo size.

The producer only modifies wpos while the consumer only modifies rpos. This
makes it pretty easy to reason about and make the operations thread safe by
using barriers (thread safety is guaranteed only in the Single-Producer/Single-
Consumer case).

Also adapted ao_coreaudio to use this ringbuffer.

1 files changed, 23 insertions, 0 deletions

diff --git a/core/mp_memory_barrier.h b/core/mp_memory_barrier.h
new file mode 100644
index 0000000000..e27825de8f
--- /dev/null
+++ b/core/mp_memory_barrier.h
@@ -0,0 +1,23 @@
+/*
+ * This file is part of mpv.
+ * Copyright (c) 2013 Stefano Pigozzi <stefano.pigozzi@gmail.com>
+ *
+ * mpv is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * mpv is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with mpv.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+// At this point both gcc and clang had __sync_synchronize support for some
+// time. We only support a full memory barrier.
+
+#define mp_memory_barrier()           __sync_synchronize()
+#define mp_atomic_add_and_fetch(a, b) __sync_add_and_fetch(a, b)