MirroredChunk.h

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#ifndef Cpl_Persistent_Mirrored_Chunk_h_
#define Cpl_Persistent_Mirrored_Chunk_h_
/*-----------------------------------------------------------------------------
* This file is part of the Colony.Core Project.  The Colony.Core Project is an
* open source project with a BSD type of licensing agreement.  See the license
* agreement (license.txt) in the top/ directory or on the Internet at
* http://integerfox.com/colony.core/license.txt
*
* Copyright (c) 2014-2022  John T. Taylor
*
* Redistributions of the source code must retain the above copyright notice.
*----------------------------------------------------------------------------*/
/** @file */
 
 
#include "Cpl/Persistent/Chunk.h"
#include "Cpl/Persistent/RegionMedia.h"
#include <stdint.h>
 
///
namespace Cpl {
///
namespace Persistent {
 
 
/** This concrete class implements the Chunk interface by storing two copies
    of the Record's data.  This ensures that if power fails during a write
    operation to persistent media - there will also be a good 'previous' copy
    of the data available.
 */
class MirroredChunk: public Chunk
{
public:
    /// Length of the data
    constexpr static size_t FRAME_OFFSET_DATA_LEN = sizeof(uint64_t);
    
    /// Start of data (aka overhead length)
    constexpr static size_t FRAME_OFFSET_DATA = sizeof( size_t ) + FRAME_OFFSET_DATA_LEN;
 
    /// The size of the CRC
    constexpr static size_t CRC_SIZE = sizeof( uint32_t );
 
    /// Total overhead size
    constexpr static size_t FRAME_OVERHEAD = FRAME_OFFSET_DATA + CRC_SIZE;
 
 
public:
    /// Constructor
    MirroredChunk( RegionMedia& regionA, RegionMedia& regionB );
 
public:
    /// See Cpl::Persistent::Chunk
    void start( Cpl::Dm::MailboxServer& myMbox ) noexcept;
 
    /// See Cpl::Persistent::Chunk
    void stop() noexcept;
 
    /// See Cpl::Persistent::Chunk
    bool loadData( Payload& dstHandler, size_t index=0  ) noexcept;
 
    /// See Cpl::Persistent::Chunk
    bool updateData( Payload& srcHandler, size_t index=0, bool invalidate=false  ) noexcept;
 
    /// See Cpl::Persistent::Chunk
    size_t getMetadataLength() const noexcept;
 
protected:
    /// Helper method.  If the region is 'corrupt' a transaction ID of zero is returned
    uint64_t virtual getTransactionId( RegionMedia& region, size_t& dataLen, size_t index=0  );
 
    /// Helper method. Encapsulates pushing data to the record
    virtual bool pushToRecord(Payload& dstHandler);
 
    /// Helper method. Encapsulates retrieving data from the record. Returns the length of the data
    virtual size_t pullFromRecord( Payload& srcHandler );
 
    /// Helper method. Encapsulates actions that occur when there is NO VALID data
    virtual void reset();
 
 
protected:
    /// Region/Media for copy A
    RegionMedia& m_regionA;
 
    /// Region/Media for copy B
    RegionMedia& m_regionB;
 
    /// Current Transaction ID (the larger the value - the newer the data)
    uint64_t     m_transId;
 
    /// Data Length for the region
    size_t       m_dataLen;
 
    /// Pointer to the current region (i.e. newest read/written region)
    RegionMedia* m_currentRegion;
 
};
 
 
};      // end namespaces
};
#endif  // end header latch