Public API Reference

csutil/weakref.h

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/*
  Crystal Space Weak Reference
  Copyright (C) 2003 by Jorrit Tyberghein and Matthias Braun

  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Library General Public
  License as published by the Free Software Foundation; either
  version 2 of the License, or (at your option) any later version.

  This library is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  Library General Public License for more details.

  You should have received a copy of the GNU Library General Public
  License along with this library; if not, write to the Free
  Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/

#ifndef __CS_WEAKREF_H__
#define __CS_WEAKREF_H__

#include "csextern.h"
#include "csutil/ref.h"
#include "csutil/threading/mutex.h"

struct iBase;

/* Define this macro if you want to get a warning when a weak reference is
 * used in a way that is unsafe with multiple threads. */
#ifdef CS_WEAKREF_WARN_MULTITHREADING_UNSAFE
#define CS_WEAKREF_METHOD_UNSAFE        \
  CS_DEPRECATED_METHOD_MSG("UNSAFE in multithreading scenarios - use Get<csRef<> >()")
#else
#define CS_WEAKREF_METHOD_UNSAFE
#endif

template <class T>
class csWeakRef
{
private:
  union
  {
    T* obj;
    void* obj_void;
  };
#if defined(CS_DEBUG)
  void* this_saved;
#endif
  mutable CS::Threading::Mutex obj_mutex;

  void Unlink ()
  {
    if (obj) obj->RemoveRefOwner (&obj_void);
  }

  void Link ()
  {
    if (obj) obj->AddRefOwner (&obj_void, &obj_mutex);
  }

public:
  csWeakRef () : obj (0) 
  {
#if defined(CS_DEBUG)
    this_saved = this;
#endif
  }

  csWeakRef (T* newobj)
  {
#if defined(CS_DEBUG)
    this_saved = this;
#endif
    obj = newobj;
    Link ();
  }

  csWeakRef (csRef<T> const& newobj)
  {
#if defined(CS_DEBUG)
    this_saved = this;
#endif
    obj = newobj;
    Link ();
  }

  csWeakRef (csWeakRef const& other)
  {
#if defined(CS_DEBUG)
    this_saved = this;
#endif
    // Keep object from 'other' alive until we linked
    typename T::WeakReferencedKeepAlive other_obj_ref;
    {
      CS::Threading::ScopedLock<CS::Threading::Mutex> lock_other_mutex (other.obj_mutex);
      obj = other.obj;
      other_obj_ref = obj;
      (void)other_obj_ref;
    }
    Link ();
  }

  csWeakRef (const csPtr<T>& newobj)
  {
#if defined(CS_DEBUG)
    this_saved = this;
#endif
    csRef<T> r = newobj;
    obj = r;
    Link ();
  }

  ~csWeakRef ()
  {
#if defined(CS_DEBUG)
    CS_ASSERT_MSG ("A csWeakRef<> was memcpy()ed, which is not allowed",
      this_saved == this);
#endif
    /* We need to keep the old object alive for unlinking,
     * but we can't keep the obj_mutex locked (possible deadlock
     * when the object is in DecRef()) */
    typename T::WeakReferencedKeepAlive obj_ref (Get<typename T::WeakReferencedKeepAlive> ());
    (void)obj_ref;
    Unlink ();
  }

  csWeakRef& operator = (T* newobj)
  {
    CS::Threading::ScopedLock<CS::Threading::Mutex> lock_mutex (obj_mutex);
    if (obj != newobj)
    {
      {
        /* We need to keep the old object alive for unlinking,
         * but we can't keep the obj_mutex locked (possible deadlock
         * when the object is in DecRef()) */
        typename T::WeakReferencedKeepAlive old_obj_ref (obj);
        (void)old_obj_ref;
        obj_mutex.Unlock();
        Unlink ();
      }
      obj_mutex.Lock();
      obj = newobj;
      Link ();
    }
    return *this;
  }

  csWeakRef& operator = (csRef<T> const& newobj)
  {
    return (*this = (T*)newobj);
  }

  csWeakRef& operator = (csPtr<T> newobj)
  {
    csRef<T> r (newobj);
    return (*this = r);
  }

  csWeakRef& operator = (csWeakRef const& other)
  {
    this->operator=(other.obj);
    return *this;
  }

  inline friend bool operator == (const csWeakRef& r1, const csWeakRef& r2)
  {
    CS::Threading::ScopedLock<CS::Threading::Mutex> lock_mutex1 (r1.obj_mutex);
    CS::Threading::ScopedLock<CS::Threading::Mutex> lock_mutex2 (r2.obj_mutex);
    return r1.obj == r2.obj;
  }
  inline friend bool operator != (const csWeakRef& r1, const csWeakRef& r2)
  {
    CS::Threading::ScopedLock<CS::Threading::Mutex> lock_mutex1 (r1.obj_mutex);
    CS::Threading::ScopedLock<CS::Threading::Mutex> lock_mutex2 (r2.obj_mutex);
    return r1.obj != r2.obj;
  }
  inline friend bool operator == (const csWeakRef& r1, T* obj)
  {
    CS::Threading::ScopedLock<CS::Threading::Mutex> lock_mutex1 (r1.obj_mutex);
    return r1.obj == obj;
  }
  inline friend bool operator != (const csWeakRef& r1, T* obj)
  {
    CS::Threading::ScopedLock<CS::Threading::Mutex> lock_mutex1 (r1.obj_mutex);
    return r1.obj != obj;
  }
  inline friend bool operator == (T* obj, const csWeakRef& r1)
  {
    CS::Threading::ScopedLock<CS::Threading::Mutex> lock_mutex1 (r1.obj_mutex);
    return r1.obj == obj;
  }
  inline friend bool operator != (T* obj, const csWeakRef& r1)
  {
    CS::Threading::ScopedLock<CS::Threading::Mutex> lock_mutex1 (r1.obj_mutex);
    return r1.obj != obj;
  }

  inline friend bool operator < (const csWeakRef& r1, const csWeakRef& r2)
  {
    CS::Threading::ScopedLock<CS::Threading::Mutex> lock_mutex1 (r1.obj_mutex);
    CS::Threading::ScopedLock<CS::Threading::Mutex> lock_mutex2 (r2.obj_mutex);
    return r1.obj < r2.obj;
  }

  CS_WEAKREF_METHOD_UNSAFE
  T* operator -> () const
  { return obj; }
  
  CS_WEAKREF_METHOD_UNSAFE
  operator T* () const
  { return obj; }
  
  CS_WEAKREF_METHOD_UNSAFE
  T& operator* () const
  { return *obj; }


  template<typename U>
  U Get() const
  {
    CS::Threading::ScopedLock<CS::Threading::Mutex> lock_mutex (obj_mutex);
    return U (obj);
  }
  template<typename U>
  void Get(U& ref) const
  {
    CS::Threading::ScopedLock<CS::Threading::Mutex> lock_mutex (obj_mutex);
    ref = obj;
  }


  CS_WEAKREF_METHOD_UNSAFE
  bool IsValid () const
  { return (obj != 0); }

  uint GetHash() const
  {
    CS::Threading::ScopedLock<CS::Threading::Mutex> lock_mutex (obj_mutex);
    return (uintptr_t)obj;    
  }
};

#endif // __CS_WEAKREF_H__

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