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.

15 files changed, 417 insertions, 401 deletions

diff --git a/Makefile.am b/Makefile.am
index cbd2fc9b..25478f81 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -84,6 +84,7 @@ mpd_headers = \
 	src/daemon.h \
 	src/normalize.h \
 	src/compress.h \
+	src/buffer.h \
 	src/pipe.h \
 	src/chunk.h \
 	src/path.h \
@@ -180,6 +181,7 @@ src_mpd_SOURCES = \
 	src/daemon.c \
 	src/normalize.c \
 	src/compress.c \
+	src/buffer.c \
 	src/pipe.c \
 	src/chunk.c \
 	src/path.c \
diff --git a/src/buffer.c b/src/buffer.c
new file mode 100644
index 00000000..1b300887
--- /dev/null
+++ b/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);
+}
diff --git a/src/buffer.h b/src/buffer.h
new file mode 100644
index 00000000..3bbee2e6
--- /dev/null
+++ b/src/buffer.h
@@ -0,0 +1,66 @@
+/*
+ * 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
+ */
+
+#ifndef MPD_MUSIC_BUFFER_H
+#define MPD_MUSIC_BUFFER_H
+
+/**
+ * An allocator for #music_chunk objects.
+ */
+struct music_buffer;
+
+/**
+ * Creates a new #music_buffer object.
+ *
+ * @param num_chunks the number of #music_chunk reserved in this
+ * buffer
+ */
+struct music_buffer *
+music_buffer_new(unsigned num_chunks);
+
+/**
+ * Frees the #music_buffer object
+ */
+void
+music_buffer_free(struct music_buffer *buffer);
+
+/**
+ * Returns the total number of reserved chunks in this buffer.  This
+ * is the same value which was passed to the constructor
+ * music_buffer_new().
+ */
+unsigned
+music_buffer_size(const struct music_buffer *buffer);
+
+/**
+ * Allocates a chunk from the buffer.  When it is not used anymore,
+ * call music_buffer_return().
+ *
+ * @return an empty chunk or NULL if there are no chunks available
+ */
+struct music_chunk *
+music_buffer_allocate(struct music_buffer *buffer);
+
+/**
+ * Returns a chunk to the buffer.  It can be reused by
+ * music_buffer_allocate() then.
+ */
+void
+music_buffer_return(struct music_buffer *buffer, struct music_chunk *chunk);
+
+#endif
diff --git a/src/chunk.h b/src/chunk.h
index 58ed7be6..b6346610 100644
--- a/src/chunk.h
+++ b/src/chunk.h
@@ -35,6 +35,9 @@ struct audio_format;
  * music_pipe_append() caller.
  */
 struct music_chunk {
+	/** the next chunk in a linked list */
+	struct music_chunk *next;
+
 	/** number of bytes stored in this chunk */
 	uint16_t length;
 
diff --git a/src/decoder_api.c b/src/decoder_api.c
index 88864bef..0992eac9 100644
--- a/src/decoder_api.c
+++ b/src/decoder_api.c
@@ -23,6 +23,7 @@
 #include "player_control.h"
 #include "audio.h"
 #include "song.h"
+#include "buffer.h"
 
 #include "normalize.h"
 #include "pipe.h"
@@ -90,11 +91,11 @@ void decoder_command_finished(G_GNUC_UNUSED struct decoder * decoder)
 		/* delete frames from the old song position */
 
 		if (decoder->chunk != NULL) {
-			music_pipe_cancel(decoder->chunk);
+			music_buffer_return(dc.buffer, decoder->chunk);
 			decoder->chunk = NULL;
 		}
 
-		music_pipe_clear();
+		music_pipe_clear(dc.pipe, dc.buffer);
 	}
 
 	dc.command = DECODE_COMMAND_NONE;
@@ -167,15 +168,18 @@ do_send_tag(struct decoder *decoder, struct input_stream *is,
 	if (decoder->chunk != NULL) {
 		/* there is a partial chunk - flush it, we want the
 		   tag in a new chunk */
-		enum decoder_command cmd =
-			decoder_flush_chunk(decoder, is);
-		if (cmd != DECODE_COMMAND_NONE)
-			return cmd;
+		decoder_flush_chunk(decoder);
+		notify_signal(&pc.notify);
 	}
 
 	assert(decoder->chunk == NULL);
 
-	chunk = decoder_get_chunk(decoder);
+	chunk = decoder_get_chunk(decoder, is);
+	if (chunk == NULL) {
+		assert(dc.command != DECODE_COMMAND_NONE);
+		return dc.command;
+	}
+
 	chunk->tag = tag_dup(tag);
 	return DECODE_COMMAND_NONE;
 }
@@ -256,15 +260,18 @@ decoder_data(struct decoder *decoder,
 		size_t nbytes;
 		bool full;
 
-		chunk = decoder_get_chunk(decoder);
+		chunk = decoder_get_chunk(decoder, is);
+		if (chunk == NULL) {
+			assert(dc.command != DECODE_COMMAND_NONE);
+			return dc.command;
+		}
+
 		dest = music_chunk_write(chunk, &dc.out_audio_format,
 					 data_time, bitRate, &nbytes);
 		if (dest == NULL) {
 			/* the chunk is full, flush it */
-			enum decoder_command cmd =
-				decoder_flush_chunk(decoder, is);
-			if (cmd != DECODE_COMMAND_NONE)
-				return cmd;
+			decoder_flush_chunk(decoder);
+			notify_signal(&pc.notify);
 			continue;
 		}
 
@@ -291,10 +298,8 @@ decoder_data(struct decoder *decoder,
 		full = music_chunk_expand(chunk, &dc.out_audio_format, nbytes);
 		if (full) {
 			/* the chunk is full, flush it */
-			enum decoder_command cmd =
-				decoder_flush_chunk(decoder, is);
-			if (cmd != DECODE_COMMAND_NONE)
-				return cmd;
+			decoder_flush_chunk(decoder);
+			notify_signal(&pc.notify);
 		}
 
 		data += nbytes;
diff --git a/src/decoder_control.h b/src/decoder_control.h
index d1d0625e..f981074d 100644
--- a/src/decoder_control.h
+++ b/src/decoder_control.h
@@ -66,6 +66,12 @@ struct decoder_control {
 	struct song *current_song;
 	struct song *next_song;
 	float total_time;
+
+	/** the #music_chunk allocator */
+	struct music_buffer *buffer;
+
+	/** the destination pipe for decoded chunks */
+	struct music_pipe *pipe;
 };
 
 extern struct decoder_control dc;
diff --git a/src/decoder_internal.c b/src/decoder_internal.c
index 93ad80e5..120115ed 100644
--- a/src/decoder_internal.c
+++ b/src/decoder_internal.c
@@ -21,6 +21,7 @@
 #include "player_control.h"
 #include "pipe.h"
 #include "input_stream.h"
+#include "buffer.h"
 
 #include <assert.h>
 
@@ -46,35 +47,32 @@ need_chunks(struct input_stream *is, bool do_wait)
 }
 
 struct music_chunk *
-decoder_get_chunk(struct decoder *decoder)
+decoder_get_chunk(struct decoder *decoder, struct input_stream *is)
 {
+	enum decoder_command cmd;
+
 	assert(decoder != NULL);
 
 	if (decoder->chunk != NULL)
 		return decoder->chunk;
 
-	decoder->chunk = music_pipe_allocate();
-	return decoder->chunk;
+	do {
+		decoder->chunk = music_buffer_allocate(dc.buffer);
+		if (decoder->chunk != NULL)
+			return decoder->chunk;
+
+		cmd = need_chunks(is, true);
+	} while (cmd == DECODE_COMMAND_NONE);
+
+	return NULL;
 }
 
-enum decoder_command
-decoder_flush_chunk(struct decoder *decoder, struct input_stream *is)
+void
+decoder_flush_chunk(struct decoder *decoder)
 {
-	bool success;
-	enum decoder_command cmd;
-
 	assert(decoder != NULL);
 	assert(decoder->chunk != NULL);
 
-	while (true) {
-		success = music_pipe_push(decoder->chunk);
-		if (success) {
-			decoder->chunk = NULL;
-			return DECODE_COMMAND_NONE;
-		}
-
-		cmd = need_chunks(is, true);
-		if (cmd != DECODE_COMMAND_NONE)
-			return cmd;
-	}
+	music_pipe_push(dc.pipe, decoder->chunk);
+	decoder->chunk = NULL;
 }
diff --git a/src/decoder_internal.h b/src/decoder_internal.h
index ab52ab03..cf46eb2c 100644
--- a/src/decoder_internal.h
+++ b/src/decoder_internal.h
@@ -42,17 +42,16 @@ struct decoder {
 /**
  * Returns the current chunk the decoder writes to, or allocates a new
  * chunk if there is none.
+ *
+ * @return the chunk, or NULL if we have received a decoder command
  */
 struct music_chunk *
-decoder_get_chunk(struct decoder *decoder);
+decoder_get_chunk(struct decoder *decoder, struct input_stream *is);
 
 /**
- * Flushes a chunk.  Waits for room in the music pipe if required.
- *
- * @return DECODE_COMMAND_NONE on success, any other command if we
- * have received a decoder command while waiting
+ * Flushes the current chunk.
  */
-enum decoder_command
-decoder_flush_chunk(struct decoder *decoder, struct input_stream *is);
+void
+decoder_flush_chunk(struct decoder *decoder);
 
 #endif
diff --git a/src/decoder_thread.c b/src/decoder_thread.c
index 97e92d29..a48f4160 100644
--- a/src/decoder_thread.c
+++ b/src/decoder_thread.c
@@ -196,9 +196,8 @@ static void decoder_run_song(const struct song *song, const char *uri)
 	pcm_convert_deinit(&decoder.conv_state);
 
 	/* flush the last chunk */
-	if (decoder.chunk != NULL &&
-	    decoder_flush_chunk(&decoder, NULL) != DECODE_COMMAND_NONE)
-		music_pipe_cancel(decoder.chunk);
+	if (decoder.chunk != NULL)
+		decoder_flush_chunk(&decoder);
 
 	if (close_instream)
 		input_stream_close(&input_stream);
diff --git a/src/main.c b/src/main.c
index 39c6a355..a3f613d0 100644
--- a/src/main.c
+++ b/src/main.c
@@ -31,7 +31,6 @@
 #include "conf.h"
 #include "path.h"
 #include "mapper.h"
-#include "pipe.h"
 #include "chunk.h"
 #include "decoder_control.h"
 #include "player_control.h"
@@ -179,8 +178,7 @@ initialize_decoder_and_player(void)
 	if (buffered_before_play > buffered_chunks)
 		buffered_before_play = buffered_chunks;
 
-	pc_init(buffered_before_play);
-	music_pipe_init(buffered_chunks, &pc.notify);
+	pc_init(buffered_chunks, buffered_before_play);
 	dc_init();
 }
 
@@ -333,7 +331,6 @@ int main(int argc, char *argv[])
 #ifdef ENABLE_ARCHIVE
 	archive_plugin_deinit_all();
 #endif
-	music_pipe_free();
 	config_global_finish();
 	tag_pool_deinit();
 	songvec_deinit();
diff --git a/src/pipe.c b/src/pipe.c
index 6f6fd816..d02a00a0 100644
--- a/src/pipe.c
+++ b/src/pipe.c
@@ -17,208 +17,103 @@
  */
 
 #include "pipe.h"
+#include "buffer.h"
 #include "chunk.h"
-#include "notify.h"
-#include "audio_format.h"
-#include "tag.h"
 
 #include <glib.h>
-#include <assert.h>
-#include <string.h>
-
-struct music_pipe music_pipe;
-
-void
-music_pipe_init(unsigned int size, struct notify *notify)
-{
-	assert(size > 0);
-
-	music_pipe.chunks = g_new(struct music_chunk, size);
-	music_pipe.num_chunks = size;
-	music_pipe.begin = 0;
-	music_pipe.end = 0;
-	music_pipe.lazy = false;
-	music_pipe.notify = notify;
-	music_chunk_init(&music_pipe.chunks[0]);
-}
-
-void music_pipe_free(void)
-{
-	assert(music_pipe.chunks != NULL);
-
-	music_pipe_clear();
-
-	g_free(music_pipe.chunks);
-}
-
-/** return the index of the chunk after i */
-static inline unsigned successor(unsigned i)
-{
-	assert(i < music_pipe.num_chunks);
-
-	++i;
-	return i == music_pipe.num_chunks ? 0 : i;
-}
-
-void music_pipe_clear(void)
-{
-	unsigned i;
-
-	for (i = music_pipe.begin; i != music_pipe.end; i = successor(i))
-		music_chunk_free(&music_pipe.chunks[i]);
-
-	music_chunk_free(&music_pipe.chunks[music_pipe.end]);
-
-	music_pipe.end = music_pipe.begin;
-	music_chunk_init(&music_pipe.chunks[music_pipe.end]);
-}
-
-/**
- * Mark the tail chunk as "full" and wake up the player if is waiting
- * for the decoder.
- */
-static void output_buffer_expand(unsigned i)
-{
-	int was_empty = music_pipe.notify != NULL && (!music_pipe.lazy || music_pipe_is_empty());
-
-	assert(i == (music_pipe.end + 1) % music_pipe.num_chunks);
-	assert(i != music_pipe.end);
-
-	music_pipe.end = i;
-	music_chunk_init(&music_pipe.chunks[i]);
-
-	if (was_empty)
-		/* if the buffer was empty, the player thread might be
-		   waiting for us; wake it up now that another decoded
-		   buffer has become available. */
-		notify_signal(music_pipe.notify);
-}
 
-void music_pipe_set_lazy(bool lazy)
-{
-	music_pipe.lazy = lazy;
-}
-
-void music_pipe_shift(void)
-{
-	assert(music_pipe.begin != music_pipe.end);
-	assert(music_pipe.begin < music_pipe.num_chunks);
+#include <assert.h>
 
-	music_chunk_free(&music_pipe.chunks[music_pipe.begin]);
+struct music_pipe {
+	/** the first chunk */
+	struct music_chunk *head;
 
-	music_pipe.begin = successor(music_pipe.begin);
-}
+	/** a pointer to the tail of the chunk */
+	struct music_chunk **tail_r;
 
-unsigned int music_pipe_relative(const unsigned i)
-{
-	if (i >= music_pipe.begin)
-		return i - music_pipe.begin;
-	else
-		return i + music_pipe.num_chunks - music_pipe.begin;
-}
+	/** the current number of chunks */
+	unsigned size;
 
-unsigned music_pipe_available(void)
-{
-	return music_pipe_relative(music_pipe.end);
-}
+	/** a mutex which protects #head and #tail_r */
+	GMutex *mutex;
+};
 
-int music_pipe_absolute(const unsigned relative)
+struct music_pipe *
+music_pipe_new(void)
 {
-	unsigned i, max;
-
-	max = music_pipe.end;
-	if (max < music_pipe.begin)
-		max += music_pipe.num_chunks;
-	i = (unsigned)music_pipe.begin + relative;
-	if (i >= max)
-		return -1;
+	struct music_pipe *mp = g_new(struct music_pipe, 1);
 
-	if (i >= music_pipe.num_chunks)
-		i -= music_pipe.num_chunks;
+	mp->head = NULL;
+	mp->tail_r = &mp->head;
+	mp->size = 0;
+	mp->mutex = g_mutex_new();
 
-	return (int)i;
+	return mp;
 }
 
-struct music_chunk *
-music_pipe_get_chunk(const unsigned i)
+void
+music_pipe_free(struct music_pipe *mp)
 {
-	assert(i < music_pipe.num_chunks);
+	assert(mp->head == NULL);
+	assert(mp->tail_r == &mp->head);
 
-	return &music_pipe.chunks[i];
+	g_mutex_free(mp->mutex);
+	g_free(mp);
 }
 
 struct music_chunk *
-music_pipe_allocate(void)
+music_pipe_shift(struct music_pipe *mp)
 {
 	struct music_chunk *chunk;
 
-	/* the music_pipe.end chunk is always kept initialized */
-	chunk = music_pipe_get_chunk(music_pipe.end);
-	assert(chunk->length == 0);
+	g_mutex_lock(mp->mutex);
 
-	return chunk;
-}
+	chunk = mp->head;
+	if (chunk != NULL) {
+		mp->head = chunk->next;
+		--mp->size;
 
-bool
-music_pipe_push(struct music_chunk *chunk)
-{
-	unsigned int next;
+		if (mp->head == NULL) {
+			assert(mp->size == 0);
+			assert(mp->tail_r == &chunk->next);
 
-	assert(chunk == music_pipe_get_chunk(music_pipe.end));
+			mp->tail_r = &mp->head;
+		} else {
+			assert(mp->size > 0);
+			assert(mp->tail_r != &chunk->next);
+		}
+	}
 
-	next = successor(music_pipe.end);
-	if (music_pipe.begin == next)
-		/* no room */
-		return false;
+	g_mutex_unlock(mp->mutex);
 
-	output_buffer_expand(next);
-	return true;
+	return chunk;
 }
 
 void
-music_pipe_cancel(struct music_chunk *chunk)
-{
-	assert(chunk == music_pipe_get_chunk(music_pipe.end));
-
-	music_chunk_free(chunk);
-}
-
-void music_pipe_skip(unsigned num)
+music_pipe_clear(struct music_pipe *mp, struct music_buffer *buffer)
 {
-	int i = music_pipe_absolute(num);
-	if (i < 0)
-		return;
+	struct music_chunk *chunk;
 
-	while (music_pipe.begin != (unsigned)i)
-		music_pipe_shift();
+	while ((chunk = music_pipe_shift(mp)) != NULL)
+		music_buffer_return(buffer, chunk);
 }
 
-void music_pipe_chop(unsigned first)
+void
+music_pipe_push(struct music_pipe *mp, struct music_chunk *chunk)
 {
-	for (unsigned i = first; i != music_pipe.end; i = successor(i))
-		music_chunk_free(&music_pipe.chunks[i]);
+	g_mutex_lock(mp->mutex);
 
-	music_chunk_free(&music_pipe.chunks[music_pipe.end]);
+	chunk->next = NULL;
+	*mp->tail_r = chunk;
+	mp->tail_r = &chunk->next;
 
-	music_pipe.end = first;
-	music_chunk_init(&music_pipe.chunks[first]);
+	++mp->size;
 
+	g_mutex_unlock(mp->mutex);
 }
 
-#ifndef NDEBUG
-void music_pipe_check_format(const struct audio_format *current,
-			     int next_index, const struct audio_format *next)
+unsigned
+music_pipe_size(const struct music_pipe *mp)
 {
-	const struct audio_format *audio_format = current;
-
-	for (unsigned i = music_pipe.begin; i != music_pipe.end;
-	     i = successor(i)) {
-		const struct music_chunk *chunk = music_pipe_get_chunk(i);
-
-		if (next_index > 0 && i == (unsigned)next_index)
-			audio_format = next;
-
-		assert(chunk->length % audio_format_frame_size(audio_format) == 0);
-	}
+	return mp->size;
 }
-#endif
diff --git a/src/pipe.h b/src/pipe.h
index 01214dc5..f1a23154 100644
--- a/src/pipe.h
+++ b/src/pipe.h
@@ -19,160 +19,51 @@
 #ifndef MPD_PIPE_H
 #define MPD_PIPE_H
 
-#include <stddef.h>
-#include <stdint.h>
-#include <stdbool.h>
-
-struct audio_format;
-struct tag;
 struct music_chunk;
+struct music_buffer;
 
 /**
- * A ring set of buffers where the decoder appends data after the end,
- * and the player consumes data from the beginning.
- */
-struct music_pipe {
-	struct music_chunk *chunks;
-	unsigned num_chunks;
-
-	/** the index of the first decoded chunk */
-	unsigned begin;
-
-	/** the index after the last decoded chunk */
-	unsigned end;
-
-	/** non-zero if the player thread should only we woken up if
-	    the buffer becomes non-empty */
-	bool lazy;
-
-	struct notify *notify;
-};
-
-extern struct music_pipe music_pipe;
-
-void
-music_pipe_init(unsigned int size, struct notify *notify);
-
-void music_pipe_free(void);
-
-void music_pipe_clear(void);
-
-/**
- * When a chunk is decoded, we wake up the player thread to tell him
- * about it.  In "lazy" mode, we only wake him up when the buffer was
- * previously empty, i.e. when the player thread has really been
- * waiting for us.
+ * A queue of #music_chunk objects.  One party appends chunks at the
+ * tail, and the other consumes them from the head.
  */
-void music_pipe_set_lazy(bool lazy);
-
-static inline unsigned
-music_pipe_size(void)
-{
-	return music_pipe.num_chunks;
-}
-
-/** is the buffer empty? */
-static inline bool music_pipe_is_empty(void)
-{
-	return music_pipe.begin == music_pipe.end;
-}
-
-static inline bool
-music_pipe_head_is(unsigned i)
-{
-	return !music_pipe_is_empty() && music_pipe.begin == i;
-}
-
-static inline unsigned
-music_pipe_tail_index(void)
-{
-	return music_pipe.end;
-}
-
-void music_pipe_shift(void);
+struct music_pipe;
 
 /**
- * what is the position of the specified chunk number, relative to
- * the first chunk in use?
+ * Creates a new #music_pipe object.  It is empty.
  */
-unsigned int music_pipe_relative(const unsigned i);
-
-/** determine the number of decoded chunks */
-unsigned music_pipe_available(void);
+struct music_pipe *
+music_pipe_new(void);
 
 /**
- * Get the absolute index of the nth used chunk after the first one.
- * Returns -1 if there is no such chunk.
+ * Frees the object.  It must be empty now.
  */
-int music_pipe_absolute(const unsigned relative);
-
-struct music_chunk *
-music_pipe_get_chunk(const unsigned i);
-
-static inline struct music_chunk *
-music_pipe_peek(void)
-{
-	if (music_pipe_is_empty())
-		return NULL;
-
-	return music_pipe_get_chunk(music_pipe.begin);
-}
+void
+music_pipe_free(struct music_pipe *mp);
 
 /**
- * Allocates a chunk for writing.  When you are finished, append it
- * with music_pipe_push().
- *
- * @return an empty chunk
+ * Removes the first chunk from the head, and returns it.
  */
 struct music_chunk *
-music_pipe_allocate(void);
-
-/**
- * Appends a chunk at the end of the music pipe.
- *
- * @param chunk a chunk allocated with music_pipe_allocate()
- * @return true on success, false if there is no room
- */
-bool
-music_pipe_push(struct music_chunk *chunk);
+music_pipe_shift(struct music_pipe *mp);
 
 /**
- * Cancels a chunk that has been allocated with music_pipe_allocate().
+ * Clears the whole pipe and returns the chunks to the buffer.
  *
- * @param chunk a chunk allocated with music_pipe_allocate()
+ * @param buffer the buffer object to return the chunks to
  */
 void
-music_pipe_cancel(struct music_chunk *chunk);
+music_pipe_clear(struct music_pipe *mp, struct music_buffer *buffer);
 
 /**
- * Prepares appending to the music pipe.  Returns a buffer where you
- * may write into.  After you are finished, call music_pipe_expand().
- *
- * @return a writable buffer
- */
-void *
-music_pipe_write(const struct audio_format *audio_format,
-		 float data_time, uint16_t bit_rate,
-		 size_t *max_length_r);
-
-/**
- * Tells the music pipe to move the end pointer, after you have
- * written to the buffer returned by music_pipe_write().
+ * Pushes a chunk to the tail of the pipe.
  */
 void
-music_pipe_expand(const struct audio_format *audio_format, size_t length);
-
-void music_pipe_skip(unsigned num);
+music_pipe_push(struct music_pipe *mp, struct music_chunk *chunk);
 
 /**
- * Chop off the tail of the music pipe, starting with the chunk at
- * index "first".
+ * Returns the number of chunks currently in this pipe.
  */
-void music_pipe_chop(unsigned first);
-
-#ifndef NDEBUG
-void music_pipe_check_format(const struct audio_format *current,
-			     int next_index, const struct audio_format *next);
-#endif
+unsigned
+music_pipe_size(const struct music_pipe *mp);
 
 #endif
diff --git a/src/player_control.c b/src/player_control.c
index 5d95fb09..4dfc810c 100644
--- a/src/player_control.c
+++ b/src/player_control.c
@@ -30,8 +30,9 @@
 
 struct player_control pc;
 
-void pc_init(unsigned int buffered_before_play)
+void pc_init(unsigned buffer_chunks, unsigned int buffered_before_play)
 {
+	pc.buffer_chunks = buffer_chunks;
 	pc.buffered_before_play = buffered_before_play;
 	notify_init(&pc.notify);
 	pc.command = PLAYER_COMMAND_NONE;
diff --git a/src/player_control.h b/src/player_control.h
index 508798ff..b1356705 100644
--- a/src/player_control.h
+++ b/src/player_control.h
@@ -60,6 +60,8 @@ enum player_error {
 };
 
 struct player_control {
+	unsigned buffer_chunks;
+
 	unsigned int buffered_before_play;
 
 	/** the handle of the player thread, or NULL if the player
@@ -84,7 +86,7 @@ struct player_control {
 
 extern struct player_control pc;
 
-void pc_init(unsigned int _buffered_before_play);
+void pc_init(unsigned buffer_chunks, unsigned buffered_before_play);
 
 void pc_deinit(void);
 
diff --git a/src/player_thread.c b/src/player_thread.c
index 678a6a3e..bb59facf 100644
--- a/src/player_thread.c
+++ b/src/player_thread.c
@@ -31,6 +31,7 @@
 #include "chunk.h"
 #include "idle.h"
 #include "main.h"
+#include "buffer.h"
 
 #include <glib.h>
 
@@ -44,6 +45,9 @@ enum xfade_state {
 };
 
 struct player {
+	struct music_buffer *buffer;
+	struct music_pipe *pipe;
+
 	/**
 	 * are we waiting for buffered_before_play?
 	 */
@@ -74,12 +78,6 @@ struct player {
 	 * is cross fading enabled?
 	 */
 	enum xfade_state xfade;
-
-	/**
-	 * index of the first chunk of the next song, -1 if there is
-	 * no next song
-	 */
-	int next_song_chunk;
 };
 
 static void player_command_finished(void)
@@ -90,6 +88,21 @@ static void player_command_finished(void)
 	notify_signal(&main_notify);
 }
 
+static void
+player_dc_stop(struct player *player)
+{
+	dc_stop(&pc.notify);
+
+	if (dc.pipe != NULL) {
+		music_pipe_clear(dc.pipe, player->buffer);
+
+		if (dc.pipe != player->pipe)
+			music_pipe_free(dc.pipe);
+
+		dc.pipe = NULL;
+	}
+}
+
 static void player_stop_decoder(void)
 {
 	dc_stop(&pc.notify);
@@ -133,9 +146,10 @@ static bool player_seek_decoder(struct player *player)
 	bool ret;
 
 	if (decoder_current_song() != pc.next_song) {
-		dc_stop(&pc.notify);
-		player->next_song_chunk = -1;
-		music_pipe_clear();
+		player_dc_stop(player);
+
+		music_pipe_clear(player->pipe, player->buffer);
+		dc.pipe = player->pipe;
 		dc_start_async(pc.next_song);
 
 		ret = player_wait_for_decoder(player);
@@ -174,7 +188,7 @@ static void player_process_command(struct player *player)
 	case PLAYER_COMMAND_QUEUE:
 		assert(pc.next_song != NULL);
 		assert(!player->queued);
-		assert(player->next_song_chunk == -1);
+		assert(dc.pipe == NULL || dc.pipe == player->pipe);
 
 		player->queued = true;
 		player_command_finished();
@@ -220,12 +234,11 @@ static void player_process_command(struct player *player)
 			return;
 		}
 
-		if (player->next_song_chunk != -1) {
+		if (dc.pipe != NULL && dc.pipe != player->pipe) {
 			/* the decoder is already decoding the song -
 			   stop it and reset the position */
+			player_dc_stop(player);
 			dc_stop(&pc.notify);
-			music_pipe_chop(player->next_song_chunk);
-			player->next_song_chunk = -1;
 		}
 
 		pc.next_song = NULL;
@@ -298,23 +311,25 @@ static void do_play(void)
 		.queued = false,
 		.song = NULL,
 		.xfade = XFADE_UNKNOWN,
-		.next_song_chunk = -1,
 	};
 	unsigned int crossFadeChunks = 0;
-	/** the position of the next cross-faded chunk in the next
-	    song */
-	int nextChunk = 0;
+	/** has cross-fading begun? */
+	bool cross_fading = false;
 	static const char silence[CHUNK_SIZE];
 	struct audio_format play_audio_format;
 	double sizeToTime = 0.0;
 
-	music_pipe_clear();
-	music_pipe_set_lazy(false);
+	player.buffer = music_buffer_new(pc.buffer_chunks);
+	player.pipe = music_pipe_new();
 
+	dc.buffer = player.buffer;
+	dc.pipe = player.pipe;
 	dc_start(&pc.notify, pc.next_song);
 	if (!player_wait_for_decoder(&player)) {
 		player_stop_decoder();
 		player_command_finished();
+		music_pipe_free(player.pipe);
+		music_buffer_free(player.buffer);
 		return;
 	}
 
@@ -332,7 +347,7 @@ static void do_play(void)
 		}
 
 		if (player.buffering) {
-			if (music_pipe_available() < pc.buffered_before_play &&
+			if (music_pipe_size(player.pipe) < pc.buffered_before_play &&
 			    !decoder_is_idle()) {
 				/* not enough decoded buffer space yet */
 				notify_wait(&pc.notify);
@@ -340,7 +355,6 @@ static void do_play(void)
 			} else {
 				/* buffering is complete */
 				player.buffering = false;
-				music_pipe_set_lazy(true);
 			}
 		}
 
@@ -395,13 +409,14 @@ static void do_play(void)
 			/* the decoder has finished the current song;
 			   make it decode the next song */
 			assert(pc.next_song != NULL);
-			assert(player.next_song_chunk == -1);
+			assert(dc.pipe == NULL || dc.pipe == player.pipe);
 
 			player.queued = false;
-			player.next_song_chunk = music_pipe_tail_index();
+			dc.pipe = music_pipe_new();
 			dc_start_async(pc.next_song);
 		}
-		if (player.next_song_chunk >= 0 &&
+
+		if (dc.pipe != NULL && dc.pipe != player.pipe &&
 		    player.xfade == XFADE_UNKNOWN &&
 		    !decoder_is_starting()) {
 			/* enable cross fading in this song?  if yes,
@@ -411,11 +426,11 @@ static void do_play(void)
 				cross_fade_calc(pc.cross_fade_seconds, dc.total_time,
 						&dc.out_audio_format,
 						&play_audio_format,
-						music_pipe_size() -
+						music_buffer_size(player.buffer) -
 						pc.buffered_before_play);
 			if (crossFadeChunks > 0) {
 				player.xfade = XFADE_ENABLED;
-				nextChunk = -1;
+				cross_fading = false;
 			} else
 				/* cross fading is disabled or the
 				   next song is too short */
@@ -424,31 +439,36 @@ static void do_play(void)
 
 		if (player.paused)
 			notify_wait(&pc.notify);
-		else if (!music_pipe_is_empty() &&
-			 !music_pipe_head_is(player.next_song_chunk)) {
-			struct music_chunk *beginChunk = music_pipe_peek();
+		else if (music_pipe_size(player.pipe) > 0) {
+			struct music_chunk *chunk = NULL;
 			unsigned int fadePosition;
+			bool success;
+
 			if (player.xfade == XFADE_ENABLED &&
-			    player.next_song_chunk >= 0 &&
-			    (fadePosition = music_pipe_relative(player.next_song_chunk))
+			    dc.pipe != NULL && dc.pipe != player.pipe &&
+			    (fadePosition = music_pipe_size(player.pipe))
 			    <= crossFadeChunks) {
 				/* perform cross fade */
-				if (nextChunk < 0) {
+				struct music_chunk *other_chunk =
+					music_pipe_shift(dc.pipe);
+
+				if (!cross_fading) {
 					/* beginning of the cross fade
 					   - adjust crossFadeChunks
 					   which might be bigger than
 					   the remaining number of
 					   chunks in the old song */
 					crossFadeChunks = fadePosition;
+					cross_fading = true;
 				}
-				nextChunk = music_pipe_absolute(crossFadeChunks);
-				if (nextChunk >= 0) {
-					music_pipe_set_lazy(true);
-					cross_fade_apply(beginChunk,
-							 music_pipe_get_chunk(nextChunk),
+
+				if (other_chunk != NULL) {
+					chunk = music_pipe_shift(player.pipe);
+					cross_fade_apply(chunk, other_chunk,
 							 &dc.out_audio_format,
 							 fadePosition,
 							 crossFadeChunks);
+					music_buffer_return(player.buffer, other_chunk);
 				} else {
 					/* there are not enough
 					   decoded chunks yet */
@@ -460,47 +480,42 @@ static void do_play(void)
 					} else {
 						/* wait for the
 						   decoder */
-						music_pipe_set_lazy(false);
 						notify_signal(&dc.notify);
 						notify_wait(&pc.notify);
 
-						/* set nextChunk to a
-						   non-negative value
-						   so the next
-						   iteration doesn't
-						   assume crossfading
-						   hasn't begun yet */
-						nextChunk = 0;
 						continue;
 					}
 				}
 			}
 
+			if (chunk == NULL)
+				chunk = music_pipe_shift(player.pipe);
+
 			/* play the current chunk */
-			if (!play_chunk(player.song, beginChunk,
-					&play_audio_format, sizeToTime))
+
+			success = play_chunk(player.song, chunk,
+					     &play_audio_format, sizeToTime);
+			music_buffer_return(player.buffer, chunk);
+
+			if (!success)
 				break;
-			music_pipe_shift();
 
 			/* this formula should prevent that the
 			   decoder gets woken up with each chunk; it
 			   is more efficient to make it decode a
 			   larger block at a time */
-			if (music_pipe_available() <= (pc.buffered_before_play + music_pipe_size() * 3) / 4)
+			if (!decoder_is_idle() &&
+			    music_pipe_size(dc.pipe) <= (pc.buffered_before_play +
+							 music_buffer_size(player.buffer) * 3) / 4)
 				notify_signal(&dc.notify);
-		} else if (music_pipe_head_is(player.next_song_chunk)) {
+		} else if (dc.pipe != NULL && dc.pipe != player.pipe) {
 			/* at the beginning of a new song */
 
-			if (player.xfade == XFADE_ENABLED && nextChunk >= 0) {
-				/* the cross-fade is finished; skip
-				   the section which was cross-faded
-				   (and thus already played) */
-				music_pipe_skip(crossFadeChunks);
-			}
-
 			player.xfade = XFADE_UNKNOWN;
 
-			player.next_song_chunk = -1;
+			music_pipe_free(player.pipe);
+			player.pipe = dc.pipe;
+
 			if (!player_wait_for_decoder(&player))
 				break;
 		} else if (decoder_is_idle()) {
@@ -524,6 +539,16 @@ static void do_play(void)
 	}
 
 	player_stop_decoder();
+
+	if (dc.pipe != NULL && dc.pipe != player.pipe) {
+		music_pipe_clear(dc.pipe, player.buffer);
+		music_pipe_free(dc.pipe);
+	}
+
+	music_pipe_clear(player.pipe, player.buffer);
+	music_pipe_free(player.pipe);
+
+	music_buffer_free(player.buffer);
 }
 
 static gpointer player_task(G_GNUC_UNUSED gpointer arg)