MusicBuffer: move code to template class SliceBuffer

1 files changed, 134 insertions, 0 deletions

diff --git a/src/util/SliceBuffer.hxx b/src/util/SliceBuffer.hxx
new file mode 100644
index 000000000..9ddad6b3d
--- /dev/null
+++ b/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