ReaderWriterLock.h

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#pragma once

#include <atomic>
#include <mutex>

namespace sw
{



class ReaderWriterLock
{
private:

    std::mutex      m_resourceLock;
    std::mutex      m_readersLock;
    int             m_numReaders;

protected:
public:
    explicit        ReaderWriterLock        () = default;
    ~ReaderWriterLock   () = default;


    inline void         ReaderLock      ();
    inline void         ReaderUnlock    ();
    inline void         WriterLock      ();
    inline void         WriterUnlock    ();
};


//====================================================================================//
//          Implementation  
//====================================================================================//


// ================================ //
//
inline void         ReaderWriterLock::ReaderLock        ()
{
    std::lock_guard< std::mutex > guard( m_readersLock );

    int prevVal = m_numReaders++;
    if( prevVal == 0 )
        m_resourceLock.lock();
}

// ================================ //
//
inline void         ReaderWriterLock::ReaderUnlock      ()
{
    std::lock_guard< std::mutex > guard( m_readersLock );

    int curVal = --m_numReaders;
    if( curVal == 0 )
        m_resourceLock.unlock();
}

// ================================ //
//
inline void         ReaderWriterLock::WriterLock        ()
{
    m_resourceLock.lock();
}

// ================================ //
//
inline void         ReaderWriterLock::WriterUnlock      ()
{
    m_resourceLock.unlock();
}

}   // sw