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+/*
+ * 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 "HugeAllocator.hxx"
+#include "gcc.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 that are initialized. This is used to
+ * avoid page faulting on the new allocation, so the kernel
+ * does not need to reserve physical memory pages.
+ */
+ unsigned n_initialized;
+
+ /**
+ * The number of slices currently allocated.
+ */
+ unsigned n_allocated;
+
+ Slice *const data;
+
+ /**
+ * Pointer to the first free element in the chain.
+ */
+ Slice *available;
+
+ size_t CalcAllocationSize() const {
+ return n_max * sizeof(Slice);
+ }
+
+public:
+ SliceBuffer(unsigned _count)
+ :n_max(_count), n_initialized(0), n_allocated(0),
+ data((Slice *)HugeAllocate(CalcAllocationSize())),
+ available(nullptr) {
+ assert(n_max > 0);
+ }
+
+ ~SliceBuffer() {
+ /* all slices must be freed explicitly, and this
+ assertion checks for leaks */
+ assert(n_allocated == 0);
+
+ HugeFree(data, CalcAllocationSize());
+ }
+
+ SliceBuffer(const SliceBuffer &other) = delete;
+ SliceBuffer &operator=(const SliceBuffer &other) = delete;
+
+ /**
+ * @return true if buffer allocation (by the constructor) has failed
+ */
+ bool IsOOM() {
+ return data == nullptr;
+ }
+
+ 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_initialized <= n_max);
+ assert(n_allocated <= n_initialized);
+
+ if (available == nullptr) {
+ if (n_initialized == n_max) {
+ /* out of (internal) memory, buffer is full */
+ assert(n_allocated == n_max);
+ return nullptr;
+ }
+
+ available = &data[n_initialized++];
+ available->next = 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_initialized <= n_max);
+ assert(n_allocated > 0);
+ assert(n_allocated <= n_initialized);
+
+ 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;
+
+ /* give memory back to the kernel when the last slice
+ was freed */
+ if (n_allocated == 0) {
+ HugeDiscard(data, CalcAllocationSize());
+ n_initialized = 0;
+ available = nullptr;
+ }
+ }
+};
+
+#endif