base_shared_ptr.hh

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/*
 * LEGAL:   COPYRIGHT (C) JIM E. BROOKS 2007
 *          THIS SOURCE CODE IS RELEASED UNDER THE TERMS
 *          OF THE GNU GENERAL PUBLIC LICENSE VERSION 2 (GPL 2).
 *****************************************************************************/


#ifndef BASE_SHARED_PTR_HH
#define BASE_SHARED_PTR_HH 1

#include "base_common.hh"

namespace base {

// Shared
//
// Clients can just derive using "public Shared" since mRefCnt is private.
// "private Shared" is ideal but every client would have to declare SharedPtr a friend.
//
class Shared
{
public:
    uint GetRefCnt( void ) const { CHECK_TYPESIG(this,TYPESIG_SHARED);
                                   return mRefCnt; }
    void IncRefCnt( void ) { ++mRefCnt; }

protected:
    // Shared initially has zero references.
    // Copy ctor makes a copy also with zero references.
    Shared( void )              : mRefCnt(0) { SET_TYPESIG(this,TYPESIG_SHARED); }
    Shared( const Shared& src ) : mRefCnt(0) { SET_TYPESIG(this,TYPESIG_SHARED); }
    ~Shared() { INVALIDATE_TYPESIG(this,TYPESIG_SHARED); }

    // operator=() is explicitly defined as NOP (compiler would copy ref-cnts).
    // Reassigning the value of a Shared should not affect ref-cnts.
    Shared& operator=( const Shared& src ) { return *this; }

private:
    mutable int mRefCnt;

public:
    

template<typename SHARED> friend class SharedPtr;
template<typename SHARED> friend class SharedPtrNull;
template<typename SHARED> friend class SharedPtrLocked;
template<typename SHARED> friend class SharedPtrNullLocked;
};

// A faux-pas for the sake of finer-granularity is to put the lock inside the Shared class.
// That was tried but it lead to having to acquire two locks in the copy methods which
// caused potential deadlock and code would've become convoluted to avoid deadlock.
#if COMPILE_THREADS
namespace restrict { BASE_GLOBAL FastLock gLockShared; }
#endif

// SharedPtr methods contain the macro TEST_SHARED_PTR_YIELD_CPU()
// to help better test lock contention.
#ifndef TEST_SHARED_PTR_YIELD_CPU
#define TEST_SHARED_PTR_YIELD_CPU()
#endif

#define SharedPtr SharedPtr
#define SharedPtr0 SharedPtrNull

// Explicit long names used by tests.
#define SharedPtrNoLock     SharedPtr
#define SharedPtrNullNoLock SharedPtrNull

// SharedPtr<FastLock>
#define SharedPtr  SharedPtrLocked
#define THREADABLE  Threadable
#define IF_NOT_NULL(PTR)
#define SHARED_PTR_NULL  0
#define SHARED_PTR_LOCK()   THREAD_CODE( restrict::gLockShared.Lock() )
#define SHARED_PTR_UNLOCK() THREAD_CODE( restrict::gLockShared.Unlock() )
#include "base_shared_ptr2.hh"
#undef SharedPtr
#undef THREADABLE
#undef IF_NOT_NULL
#undef SHARED_PTR_NULL
#undef SHARED_PTR_LOCK
#undef SHARED_PTR_UNLOCK

// SharedPtrNull<FastLock>
#define SharedPtr  SharedPtrNullLocked
#define THREADABLE  Threadable
#define IF_NOT_NULL(PTR)  if ( EX( (PTR) != (NULL) ) )
#define SHARED_PTR_NULL  1
#define SHARED_PTR_LOCK()   THREAD_CODE( restrict::gLockShared.Lock() )
#define SHARED_PTR_UNLOCK() THREAD_CODE( restrict::gLockShared.Unlock() )
#include "base_shared_ptr2.hh"
#undef SharedPtr
#undef THREADABLE
#undef IF_NOT_NULL
#undef SHARED_PTR_NULL
#undef SHARED_PTR_LOCK
#undef SHARED_PTR_UNLOCK

// SharedPtr<NoLock>
#define SharedPtr  SharedPtr
#define THREADABLE  NonThreadable
#define IF_NOT_NULL(PTR)
#define SHARED_PTR_NULL  0
#define SHARED_PTR_LOCK()
#define SHARED_PTR_UNLOCK()
#include "base_shared_ptr2.hh"
#undef SharedPtr
#undef THREADABLE
#undef IF_NOT_NULL
#undef SHARED_PTR_NULL
#undef SHARED_PTR_LOCK
#undef SHARED_PTR_UNLOCK

// SharedPtrNull<NoLock>
#define SharedPtr  SharedPtrNull
#define THREADABLE  NonThreadable
#define IF_NOT_NULL(PTR)  if ( EX( (PTR) != (NULL) ) )
#define SHARED_PTR_NULL  1
#define SHARED_PTR_LOCK()
#define SHARED_PTR_UNLOCK()
#include "base_shared_ptr2.hh"
#undef SharedPtr
#undef THREADABLE
#undef IF_NOT_NULL
#undef SHARED_PTR_NULL
#undef SHARED_PTR_LOCK
#undef SHARED_PTR_UNLOCK

} // namespace base

#endif // BASE_SHARED_PTR_HH

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