SharedResourcePointer.h

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/*
  ==============================================================================
 
   This file is part of the Water library.
   Copyright (c) 2016 ROLI Ltd.
   Copyright (C) 2017-2019 Filipe Coelho <falktx@falktx.com>
 
   Permission is granted to use this software under the terms of the ISC license
   http://www.isc.org/downloads/software-support-policy/isc-license/
 
   Permission to use, copy, modify, and/or distribute this software for any
   purpose with or without fee is hereby granted, provided that the above
   copyright notice and this permission notice appear in all copies.
 
   THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH REGARD
   TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
   FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT,
   OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF
   USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
   TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
   OF THIS SOFTWARE.
 
  ==============================================================================
*/
 
#ifndef WATER_SHAREDRESOURCEPOINTER_H_INCLUDED
#define WATER_SHAREDRESOURCEPOINTER_H_INCLUDED
 
#include "ReferenceCountedObject.h"
#include "../threads/SpinLock.h"
 
#include "CarlaScopeUtils.hpp"
 
namespace water {
 
//==============================================================================
template <typename SharedObjectType>
class SharedResourcePointer
{
public:
    SharedResourcePointer()
      : sharedObject(nullptr)
    {
        initialise();
    }
 
    SharedResourcePointer(const char* const v1, const char* const v2)
      : sharedObject(nullptr)
    {
        initialise_v2(v1, v2);
    }
 
    SharedResourcePointer (const SharedResourcePointer&)
      : sharedObject(nullptr)
    {
        initialise();
    }

    ~SharedResourcePointer()
    {
        SharedObjectHolder& holder = getSharedObjectHolder();
        const SpinLock::ScopedLockType sl (holder.lock);
 
        if (--(holder.refCount) == 0)
            holder.sharedInstance = nullptr;
    }

    operator SharedObjectType*() const noexcept         { return sharedObject; }

    SharedObjectType& get() const noexcept              { return *sharedObject; }

    SharedObjectType& getObject() const noexcept        { return *sharedObject; }
    SharedObjectType* getPointer() const noexcept       { return sharedObject; }
 
    SharedObjectType* operator->() const noexcept       { return sharedObject; }
 
private:
    struct SharedObjectHolder  : public ReferenceCountedObject
    {
        SpinLock lock;
        CarlaScopedPointer<SharedObjectType> sharedInstance;
        int refCount;
    };
 
    static SharedObjectHolder& getSharedObjectHolder() noexcept
    {
        static void* holder [(sizeof (SharedObjectHolder) + sizeof(void*) - 1) / sizeof(void*)] = { nullptr };
        return *reinterpret_cast<SharedObjectHolder*> (holder);
    }
 
    SharedObjectType* sharedObject;
 
    void initialise()
    {
        SharedObjectHolder& holder = getSharedObjectHolder();
        const SpinLock::ScopedLockType sl (holder.lock);
 
        if (++(holder.refCount) == 1)
            holder.sharedInstance = new SharedObjectType();
 
        sharedObject = holder.sharedInstance;
    }
 
    void initialise_v2(const char* const v1, const char* const v2)
    {
        SharedObjectHolder& holder = getSharedObjectHolder();
        const SpinLock::ScopedLockType sl (holder.lock);
 
        if (++(holder.refCount) == 1)
            holder.sharedInstance = new SharedObjectType(v1, v2);
 
        sharedObject = holder.sharedInstance;
    }
 
    // There's no need to assign to a SharedResourcePointer because every
    // instance of the class is exactly the same!
    SharedResourcePointer& operator= (const SharedResourcePointer&) WATER_DELETED_FUNCTION;
};
 
}
 
#endif // WATER_SHAREDRESOURCEPOINTER_H_INCLUDED