mpd/src/util/HugeAllocator.hxx

/*
 * Copyright (C) 2013-2017 Max Kellermann <max.kellermann@gmail.com>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *
 * - Redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the
 * distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
 * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#ifndef HUGE_ALLOCATOR_HXX
#define HUGE_ALLOCATOR_HXX

#include "Compiler.h"

#include <utility>

#include <stddef.h>

#ifdef __linux__

/**
 * Allocate a huge amount of memory.  This will be done in a way that
 * allows giving the memory back to the kernel as soon as we don't
 * need it anymore.  On the downside, this call is expensive.
 */
gcc_malloc
void *
HugeAllocate(size_t size);

/**
 * @param p an allocation returned by HugeAllocate()
 * @param size the allocation's size as passed to HugeAllocate()
 */
void
HugeFree(void *p, size_t size) noexcept;

/**
 * Discard any data stored in the allocation and give the memory back
 * to the kernel.  After returning, the allocation still exists and
 * can be reused at any time, but its contents are undefined.
 *
 * @param p an allocation returned by HugeAllocate()
 * @param size the allocation's size as passed to HugeAllocate()
 */
void
HugeDiscard(void *p, size_t size) noexcept;

#elif defined(WIN32)
#include <windows.h>

gcc_malloc
void *
HugeAllocate(size_t size);

static inline void
HugeFree(void *p, gcc_unused size_t size) noexcept
{
	VirtualFree(p, 0, MEM_RELEASE);
}

static inline void
HugeDiscard(void *p, size_t size) noexcept
{
	VirtualAlloc(p, size, MEM_RESET, PAGE_NOACCESS);
}

#else

/* not Linux: fall back to standard C calls */

#include <stdint.h>

gcc_malloc
static inline void *
HugeAllocate(size_t size)
{
	return new uint8_t[size];
}

static inline void
HugeFree(void *_p, size_t) noexcept
{
	auto *p = (uint8_t *)_p;
	delete[] p;
}

static inline void
HugeDiscard(void *, size_t) noexcept
{
}

#endif

/**
 * Automatic huge memory allocation management.
 */
class HugeAllocation {
	void *data = nullptr;
	size_t size;

public:
	HugeAllocation() = default;

	HugeAllocation(size_t _size)
		:data(HugeAllocate(_size)), size(_size) {}

	HugeAllocation(HugeAllocation &&src) noexcept
		:data(src.data), size(src.size) {
		src.data = nullptr;
	}

	~HugeAllocation() {
		if (data != nullptr)
			HugeFree(data, size);
	}

	HugeAllocation &operator=(HugeAllocation &&src) noexcept {
		std::swap(data, src.data);
		std::swap(size, src.size);
		return *this;
	}

	void Discard() noexcept {
		HugeDiscard(data, size);
	}

	void reset() noexcept {
		if (data != nullptr) {
			HugeFree(data, size);
			data = nullptr;
		}
	}

	void *get() noexcept {
		return data;
	}
};

#endif