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// Copyright (c) 2020 Egor Tensin <Egor.Tensin@gmail.com>
// This file is part of the "winapi-common" project.
// For details, see https://github.com/egor-tensin/winapi-common.
// Distributed under the MIT License.
#pragma once
#include "handle.hpp"
#include <cstddef>
#include <memory>
#include <string>
#include <type_traits>
#include <utility>
namespace winapi {
/** @brief Named shared memory region. */
class SharedMemory {
public:
/**
* Creates a shared memory region.
* @param name UTF-8 string.
* @param nb Number of bytes.
*/
static SharedMemory create(const std::string& name, std::size_t nb);
/**
* Opens a shared memory region.
* @param name UTF-8 string.
*/
static SharedMemory open(const std::string& name);
/** Get pointer to the data. */
void* get() const { return m_addr.get(); }
/** @overload */
void* ptr() const { return get(); }
private:
struct Unmap {
void operator()(void*) const;
};
SharedMemory() = default;
SharedMemory(Handle&& handle, void* addr) : m_handle{std::move(handle)}, m_addr{addr} {}
Handle m_handle;
std::unique_ptr<void, Unmap> m_addr;
};
/** @brief Easy way to represent a C++ object as a shared memory region. */
template <typename T>
class SharedObject {
public:
typedef typename std::aligned_storage<sizeof(T), __alignof(T)>::type AlignedType;
/**
* Create the object & construct a shared memory region to store it.
* @param name UTF-8 string, name of the shared memory region.
* @param args Arguments to construct the object.
*/
template <typename... Args>
static SharedObject create(const std::string& name, Args&&... args) {
SharedObject obj{SharedMemory::create(name, sizeof(AlignedType))};
new (obj.ptr()) T(std::forward<Args>(args)...);
obj.m_destruct = true;
return obj;
}
/**
* Open a shared memory region that stores the object.
* @param name UTF-8 string, name of the shared memory region.
*/
static SharedObject open(const std::string& name) {
SharedObject obj{SharedMemory::open(name)};
return obj;
}
SharedObject(SharedObject&& other) noexcept = default;
SharedObject& operator=(const SharedObject& other) noexcept = default;
SharedObject(const SharedObject&) = delete;
~SharedObject() {
if (m_destruct && ptr()) {
ptr()->~T();
}
}
/** Get pointer to the object. */
T* ptr() const { return reinterpret_cast<T*>(m_shmem.ptr()); }
/** Get reference to the object. */
T& get() const { return *ptr(); }
T* operator->() const { return ptr(); }
T& operator*() const { return get(); }
private:
explicit SharedObject(SharedMemory&& shmem) : m_shmem(std::move(shmem)) {}
SharedMemory m_shmem;
// Destruct only once, no matter the number of mappings.
bool m_destruct = false;
};
} // namespace winapi
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