MusicBuffer: move code to template class SliceBuffer

Makefile.am

@@ -347,6 +347,7 @@ endif
 # Generic utility library
 
 libutil_a_SOURCES = \
+	src/util/SliceBuffer.hxx \
 	src/util/list.h \
 	src/util/list_sort.c src/util/list_sort.h \
 	src/util/byte_reverse.c src/util/byte_reverse.h \

src/MusicBuffer.cxx

@@ -20,53 +20,22 @@
 #include "config.h"
 #include "MusicBuffer.hxx"
 #include "MusicChunk.hxx"
+#include "util/SliceBuffer.hxx"
 
 #include <glib.h>
 
 #include <assert.h>
 
-struct music_buffer {
-	struct music_chunk *chunks;
-	unsigned num_chunks;
-
-	struct music_chunk *available;
-
+struct music_buffer : public SliceBuffer<music_chunk>  {
 	/** a mutex which protects #available */
 	GMutex *mutex;
 
-#ifndef NDEBUG
-	unsigned num_allocated;
-#endif
-
-	music_buffer(unsigned _num_chunks)
-		:chunks(g_new(struct music_chunk, _num_chunks)),
-		 num_chunks(_num_chunks),
-		 available(chunks),
-		 mutex(g_mutex_new())
-#ifndef NDEBUG
-		, num_allocated(0)
-#endif
-	{
-		assert(num_chunks > 0);
-
-		struct music_chunk *chunk;
-		chunk = available = chunks;
-
-		for (unsigned i = 1; i < num_chunks; ++i) {
-			chunk->next = &chunks[i];
-			chunk = chunk->next;
-		}
-
-		chunk->next = nullptr;
-	}
+	music_buffer(unsigned num_chunks)
+		:SliceBuffer(num_chunks),
+		 mutex(g_mutex_new()) {}
 
 	~music_buffer() {
-		assert(chunks != nullptr);
-		assert(num_chunks > 0);
-		assert(num_allocated == 0);
-
 		g_mutex_free(mutex);
-		g_free(chunks);
 	}
 };
 
@@ -85,26 +54,14 @@ music_buffer_free(struct music_buffer *buffer)
 unsigned
 music_buffer_size(const struct music_buffer *buffer)
 {
-	return buffer->num_chunks;
+	return buffer->GetCapacity();
 }
 
 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
-	}
-
+	struct music_chunk *chunk = buffer->Allocate();
 	g_mutex_unlock(buffer->mutex);
 	return chunk;
 }
@@ -115,19 +72,14 @@ music_buffer_return(struct music_buffer *buffer, struct music_chunk *chunk)
 	assert(buffer != NULL);
 	assert(chunk != NULL);
 
-	if (chunk->other != NULL)
-		music_buffer_return(buffer, chunk->other);
-
 	g_mutex_lock(buffer->mutex);
 
-	music_chunk_free(chunk);
+	if (chunk->other != nullptr) {
+		assert(chunk->other->other == nullptr);
+		buffer->Free(chunk->other);
+	}
 
-	chunk->next = buffer->available;
-	buffer->available = chunk;
-
-#ifndef NDEBUG
-	--buffer->num_allocated;
-#endif
+	buffer->Free(chunk);
 
 	g_mutex_unlock(buffer->mutex);
 }

src/util/SliceBuffer.hxx

@@ -0,0 +1,134 @@
+/*
+ * Copyright (C) 2003-2013 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.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_SLICE_BUFFER_HXX
+#define MPD_SLICE_BUFFER_HXX
+
+#include "gcc.h"
+
+#include <glib.h>
+
+#include <utility>
+#include <new>
+
+#include <assert.h>
+#include <stddef.h>
+
+/**
+ * This class pre-allocates a certain number of objects, and allows
+ * callers to allocate and free these objects ("slices").
+ */
+template<typename T>
+class SliceBuffer {
+	union Slice {
+		Slice *next;
+
+		T value;
+	};
+
+	/**
+	 * The maximum number of slices in this container.
+	 */
+	const unsigned n_max;
+
+	/**
+	 * The number of slices currently allocated.
+	 */
+	unsigned n_allocated;
+
+	Slice *const data;
+
+	/**
+	 * Pointer to the first free element in the chain.
+	 */
+	Slice *available;
+
+public:
+	SliceBuffer(unsigned _count)
+		:n_max(_count), n_allocated(0),
+		 data(g_new(Slice, n_max)), available(data) {
+		assert(n_max > 0);
+
+		Slice *const last = data + n_max - 1;
+		for (Slice *slice = data; slice != last; ++slice)
+			slice->next = slice + 1;
+
+		last->next = nullptr;
+	}
+
+	~SliceBuffer() {
+		/* all slices must be freed explicitly, and this
+		   assertion checks for leaks */
+		assert(n_allocated == 0);
+
+		g_free(data);
+	}
+
+	SliceBuffer(const SliceBuffer &other) = delete;
+	SliceBuffer &operator=(const SliceBuffer &other) = delete;
+
+	unsigned GetCapacity() const {
+		return n_max;
+	}
+
+	bool IsEmpty() const {
+		return n_allocated == 0;
+	}
+
+	bool IsFull() const {
+		return n_allocated == n_max;
+	}
+
+	template<typename... Args>
+	T *Allocate(Args&&... args) {
+		assert(n_allocated <= n_max);
+
+		if (available == nullptr) {
+			/* out of (internal) memory, buffer is full */
+			assert(n_allocated == n_max);
+			return nullptr;
+		}
+
+		/* allocate a slice */
+		T *value = &available->value;
+		available = available->next;
+		++n_allocated;
+
+		/* construct the object */
+		return ::new((void *)value) T(std::forward<Args>(args)...);
+	}
+
+	void Free(T *value) {
+		assert(n_allocated > 0);
+		assert(n_allocated <= n_max);
+
+		Slice *slice = reinterpret_cast<Slice *>(value);
+		assert(slice >= data && slice < data + n_max);
+
+		/* destruct the object */
+		value->~T();
+
+		/* insert the slice in the "available" linked list */
+		slice->next = available;
+		available = slice;
+		--n_allocated;
+	}
+};
+
+#endif