pipe: added music_buffer, rewrite music_pipe

Turn the music_pipe into a simple music_chunk queue.  The music_chunk
allocation code is moved to music_buffer, and is now managed with a
linked list instead of a ring buffer.  Two separate music_pipe objects
are used by the decoder for the "current" and the "next" song, which
greatly simplifies the cross-fading code.

src/buffer.c

@@ -0,0 +1,127 @@
+/*
+ * Copyright (C) 2003-2009 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program 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.
+ *
+ * This program 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 this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#include "buffer.h"
+#include "chunk.h"
+
+#include <glib.h>
+
+#include <assert.h>
+
+struct music_buffer {
+	struct music_chunk *chunks;
+	unsigned num_chunks;
+
+	struct music_chunk *available;
+
+	/** a mutex which protects #available */
+	GMutex *mutex;
+
+#ifndef NDEBUG
+	unsigned num_allocated;
+#endif
+};
+
+struct music_buffer *
+music_buffer_new(unsigned num_chunks)
+{
+	struct music_buffer *buffer;
+	struct music_chunk *chunk;
+
+	assert(num_chunks > 0);
+
+	buffer = g_new(struct music_buffer, 1);
+
+	buffer->chunks = g_new(struct music_chunk, num_chunks);
+	buffer->num_chunks = num_chunks;
+
+	chunk = buffer->available = buffer->chunks;
+
+	for (unsigned i = 1; i < num_chunks; ++i) {
+		chunk->next = &buffer->chunks[i];
+		chunk = chunk->next;
+	}
+
+	chunk->next = NULL;
+
+	buffer->mutex = g_mutex_new();
+
+#ifndef NDEBUG
+	buffer->num_allocated = 0;
+#endif
+
+	return buffer;
+}
+
+void
+music_buffer_free(struct music_buffer *buffer)
+{
+	assert(buffer->chunks != NULL);
+	assert(buffer->num_chunks > 0);
+	assert(buffer->num_allocated == 0);
+
+	g_mutex_free(buffer->mutex);
+	g_free(buffer->chunks);
+	g_free(buffer);
+}
+
+unsigned
+music_buffer_size(const struct music_buffer *buffer)
+{
+	return buffer->num_chunks;
+}
+
+struct music_chunk *
+music_buffer_allocate(struct music_buffer *buffer)
+{
+	struct music_chunk *chunk;
+
+	g_mutex_lock(buffer->mutex);
+
+	chunk = buffer->available;
+	if (chunk != NULL) {
+		buffer->available = chunk->next;
+		music_chunk_init(chunk);
+
+#ifndef NDEBUG
+		++buffer->num_allocated;
+#endif
+	}
+
+	g_mutex_unlock(buffer->mutex);
+	return chunk;
+}
+
+void
+music_buffer_return(struct music_buffer *buffer, struct music_chunk *chunk)
+{
+	assert(buffer != NULL);
+	assert(chunk != NULL);
+
+	g_mutex_lock(buffer->mutex);
+
+	music_chunk_free(chunk);
+	chunk->next = buffer->available;
+	buffer->available = chunk;
+
+#ifndef NDEBUG
+	--buffer->num_allocated;
+#endif
+
+	g_mutex_unlock(buffer->mutex);
+}