ClickHouse/base/poco/Foundation/include/Poco/SharedMemory.h

//
// SharedMemory.h
//
// Library: Foundation
// Package: Processes
// Module:  SharedMemory
//
// Definition of the SharedMemory class.
//
// Copyright (c) 2007, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// SPDX-License-Identifier:	BSL-1.0
//


#ifndef Foundation_SharedMemory_INCLUDED
#define Foundation_SharedMemory_INCLUDED


#include <algorithm>
#include <cstddef>
#include "Poco/Foundation.h"


namespace Poco
{


class SharedMemoryImpl;
class File;


class Foundation_API SharedMemory
/// Create and manage a shared memory object.
///
/// A SharedMemory object has value semantics, but
/// is implemented using a handle/implementation idiom.
/// Therefore, multiple SharedMemory objects can share
/// a single, reference counted SharedMemoryImpl object.
{
public:
    enum AccessMode
    {
        AM_READ = 0,
        AM_WRITE
    };

    SharedMemory();
    /// Default constructor creates an unmapped SharedMemory object.
    /// No clients can connect to an unmapped SharedMemory object.

    SharedMemory(const std::string & name, std::size_t size, AccessMode mode, const void * addrHint = 0, bool server = true);
    /// Creates or connects to a shared memory object with the given name.
    ///
    /// For maximum portability, name should be a valid Unix filename and not
    /// contain any slashes or backslashes.
    ///
    /// An address hint can be passed to the system, specifying the desired
    /// start address of the shared memory area. Whether the hint
    /// is actually honored is, however, up to the system. Windows platform
    /// will generally ignore the hint.
    ///
    /// If server is set to true, the shared memory region will be unlinked
    /// by calling shm_unlink() (on POSIX platforms) when the SharedMemory object is destroyed.
    /// The server parameter is ignored on Windows platforms.

    SharedMemory(const File & file, AccessMode mode, const void * addrHint = 0);
    /// Maps the entire contents of file into a shared memory segment.
    ///
    /// An address hint can be passed to the system, specifying the desired
    /// start address of the shared memory area. Whether the hint
    /// is actually honored is, however, up to the system. Windows platform
    /// will generally ignore the hint.

    SharedMemory(const SharedMemory & other);
    /// Creates a SharedMemory object by copying another one.

    ~SharedMemory();
    /// Destroys the SharedMemory.

    SharedMemory & operator=(const SharedMemory & other);
    /// Assigns another SharedMemory object.

    void swap(SharedMemory & other);
    /// Swaps the SharedMemory object with another one.

    char * begin() const;
    /// Returns the start address of the shared memory segment.
    /// Will be NULL for illegal segments.

    char * end() const;
    /// Returns the one-past-end end address of the shared memory segment.
    /// Will be NULL for illegal segments.

private:
    SharedMemoryImpl * _pImpl;
};


//
// inlines
//
inline void SharedMemory::swap(SharedMemory & other)
{
    using std::swap;
    swap(_pImpl, other._pImpl);
}


} // namespace Poco::Poco


#endif // Foundation_SharedMemory_INCLUDED