RWLock.h

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/*--------------------------------------------------------------------------------------------
Copyright (c) 2019, NDEVR LLC
tyler.parke@ndevr.org
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 |  \  |  | |  __ \  |  ___|\ \   / / |   __  \
 |   \ |  | | |  \ \ | |___  \ \ / /  |  |__)  |
 |  . \|  | | |__/ / | |___   \ V /   |   _   /
 |  |\    |_|_____/__|_____|___\_/____|  | \  \
 |__| \__________________________________|  \__\
 
Subject to the terms of the Enterprise+ Agreement, NDEVR hereby grants 
Licensee a limited, non-exclusive, non-transferable, royalty-free license 
(without the right to sublicense) to use the API solely for the purpose of 
Licensee's internal development efforts to develop applications for which 
the API was provided.
 
The above copyright notice and this permission notice shall be included in all 
copies or substantial portions of the Software.
 
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
DEALINGS IN THE SOFTWARE.
 
Library: Base
File: RWLock
Included in API: True
Author(s): Tyler Parke
 *-----------------------------------------------------------------------------------------**/
#pragma once
#include "DLLInfo.h"
#include <NDEVR/BaseValues.h>
#include <NDEVR/Dictionary.h>
#include <mutex>
namespace NDEVR
{
    class UUID;
    class TimeSpan;
    /**----------------------------------------------------------------------------
    \brief Maintains a pair of associated locks, one for read-only operations and 
        one for writing. The read lock may be held simultaneously by multiple reader 
        threads, so long as there are no writers. The write lock is exclusive.
    ----------------------------------------------------------------------------*/
    class NDEVR_BASE_API RWLock
    {
    public:
        RWLock();
        RWLock(const RWLock& lock) = delete;
        ~RWLock();
 
        bool ReadLock();
        bool WriteLock();
 
        bool TryReadLock();
        bool TryWriteLock();
        
 
        bool TryReadLock(uint08 time);
        bool TryWriteLock(uint08 time);
 
        void ReadUnlock();
        void WriteUnlock();
        [[nodiscard]] uint04 numOfWriteLocksHeld() const;
        [[nodiscard]] uint04 numOfWriteLocks() const;
        [[nodiscard]] uint04 numOfReadLocksHeld() const;
        [[nodiscard]] uint04 numOfReadLocks() const;
    private:
        bool _TryReadLock();
        bool _TryWriteLock();
        
    private:
        Dictionary<uint04, uint04> m_read_owners;//Stores every thread's read counters
        std::mutex m_critical_section;//critical section for this object only
        volatile uint04 m_write_owner;//The thread that owns the write lock atm
        volatile uint04 m_readers;//The total number of reader locks held by all threads.
        volatile uint04 m_writers;//The total number of write locks held by the writer thread.
        volatile uint04 m_write_waiters;//When this is non-zero, read threads will wait. Used to prevent starvation.
    public:
 
        static RWLock* getEntry(const void* entry);
    };
    /**----------------------------------------------------------------------------
    \brief Used to lock a particular variable for reading. Any number of readers
        can be created when no write locks are on a variable, otherwise will wait. 
    
    Note: Automatically unlocks on destruction.
    ----------------------------------------------------------------------------*/
    class NDEVR_BASE_API RLock
    {
    public:
        explicit RLock(const void* lock);
        explicit RLock(const UUID& lock);
        explicit RLock(RWLock& lock);
        RLock(RLock&& lock) noexcept;
        RLock(const RLock&) = delete;
        void operator=(const RLock&) = delete;
        RLock(const void* lock, uint08 timeout);
        RLock(const void* lock, bool& didAquire);
        static bool HasLock(const void* lock);
        static bool HasLock(const RWLock& lock);
        bool isLocked() const;
        ~RLock();
    private:
        RWLock* m_lock;//pointer to the lock that will be unlocked on destructor
    };
 
    /**----------------------------------------------------------------------------
    \brief Used to lock a particular variable for writing. Only one write lock
        can be created when no read locks are on a variable, otherwise will wait.
    Note: Automatically unlocks on destruction.
    ----------------------------------------------------------------------------*/
    class NDEVR_BASE_API WLock
    {
    public:
        explicit WLock(const void* lock);
        explicit WLock(const UUID& lock);
        explicit WLock(RWLock& lock);
        WLock(WLock&& lock) noexcept;
        WLock(const WLock&) = delete;
        void operator=(const WLock&) = delete;
        WLock(const void* lock, uint08 timeout);
        WLock(const void* lock, const TimeSpan& timeout);
        bool isLocked() const;
        static bool HasLock(const void* lock);
        static bool HasLock(const RWLock& lock);
        ~WLock();
    private:
        RWLock* m_lock;//pointer to the lock that will be unlocked on destructor
    };
}