nsisupportsimpl.h

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/* ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is XPCOM.
 *
 * The Initial Developer of the Original Code is Netscape Communications Corp.
 * Portions created by the Initial Developer are Copyright (C) 2001
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either the GNU General Public License Version 2 or later (the "GPL"), or
 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the MPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the MPL, the GPL or the LGPL.
 *
 * ***** END LICENSE BLOCK ***** */


#ifndef nsISupportsImpl_h__
#define nsISupportsImpl_h__

#ifndef nscore_h___
#include "nscore.h"
#endif

#ifndef nsISupportsBase_h__
#include "nsISupportsBase.h"
#endif

#include "prthread.h" /* needed for thread-safety checks */
#include "pratom.h"   /* needed for PR_AtomicIncrement and PR_AtomicDecrement */

#include "nsDebug.h"
#include "nsTraceRefcnt.h" 

////////////////////////////////////////////////////////////////////////////////
// Macros to help detect thread-safety:

#if defined(NS_DEBUG)

class nsAutoOwningThread {
public:
    nsAutoOwningThread() { mThread = PR_GetCurrentThread(); }
    void *GetThread() const { return mThread; }

private:
    void *mThread;
};

#define NS_DECL_OWNINGTHREAD            nsAutoOwningThread _mOwningThread;
#define NS_ASSERT_OWNINGTHREAD(_class) \
  NS_CheckThreadSafe(_mOwningThread.GetThread(), #_class " not thread-safe")

#else // !(defined(NS_DEBUG))

#define NS_DECL_OWNINGTHREAD            /* nothing */
#define NS_ASSERT_OWNINGTHREAD(_class)  ((void)0)

#endif // !(defined(NS_DEBUG))

class nsAutoRefCnt {

 public:
    nsAutoRefCnt() : mValue(0) {}
    nsAutoRefCnt(nsrefcnt aValue) : mValue(aValue) {}

    // only support prefix increment/decrement
    nsrefcnt operator++() { return ++mValue; }
    nsrefcnt operator--() { return --mValue; }
    
    nsrefcnt operator=(nsrefcnt aValue) { return (mValue = aValue); }
    operator nsrefcnt() const { return mValue; }
    nsrefcnt get() const { return mValue; }
 private:
    // do not define these to enforce the faster prefix notation
    nsrefcnt operator++(int);
    nsrefcnt operator--(int);
    nsrefcnt mValue;
};

///////////////////////////////////////////////////////////////////////////////

/**
 * Declare the reference count variable and the implementations of the
 * AddRef and QueryInterface methods.
 */

#define NS_DECL_ISUPPORTS                                                     \
public:                                                                       \
  NS_IMETHOD QueryInterface(REFNSIID aIID,                                    \
                            void** aInstancePtr);                             \
  NS_IMETHOD_(nsrefcnt) AddRef(void);                                         \
  NS_IMETHOD_(nsrefcnt) Release(void);                                        \
protected:                                                                    \
  nsAutoRefCnt mRefCnt;                                                       \
  NS_DECL_OWNINGTHREAD                                                        \
public:


///////////////////////////////////////////////////////////////////////////////

/**
 * Previously used to initialize the reference count, but no longer needed.
 *
 * DEPRECATED.
 */
#define NS_INIT_ISUPPORTS() ((void)0)

/**
 * Use this macro to implement the AddRef method for a given <i>_class</i>
 * @param _class The name of the class implementing the method
 */
#define NS_IMPL_ADDREF(_class)                                                \
NS_IMETHODIMP_(nsrefcnt) _class::AddRef(void)                                 \
{                                                                             \
  NS_PRECONDITION(PRInt32(mRefCnt) >= 0, "illegal refcnt");                   \
  NS_ASSERT_OWNINGTHREAD(_class);                                             \
  ++mRefCnt;                                                                  \
  NS_LOG_ADDREF(this, mRefCnt, #_class, sizeof(*this));                       \
  return mRefCnt;                                                             \
}

/**
 * Use this macro to implement the AddRef method for a given <i>_class</i>
 * implemented as a wholly owned aggregated object intended to implement
 * interface(s) for its owner
 * @param _class The name of the class implementing the method
 * @param _aggregator the owning/containing object
 */
#define NS_IMPL_ADDREF_USING_AGGREGATOR(_class, _aggregator)                  \
NS_IMETHODIMP_(nsrefcnt) _class::AddRef(void)                                 \
{                                                                             \
  NS_PRECONDITION(_aggregator, "null aggregator");                            \
  return (_aggregator)->AddRef();                                             \
}

/**
 * Use this macro to implement the Release method for a given
 * <i>_class</i>.
 * @param _class The name of the class implementing the method
 * @param _destroy A statement that is executed when the object's
 *   refcount drops to zero.
 *
 * For example,
 *
 *   NS_IMPL_RELEASE_WITH_DESTROY(Foo, Destroy(this))
 *
 * will cause
 *
 *   Destroy(this);
 *
 * to be invoked when the object's refcount drops to zero. This
 * allows for arbitrary teardown activity to occur (e.g., deallocation
 * of object allocated with placement new).
 */
#define NS_IMPL_RELEASE_WITH_DESTROY(_class, _destroy)                        \
NS_IMETHODIMP_(nsrefcnt) _class::Release(void)                                \
{                                                                             \
  NS_PRECONDITION(0 != mRefCnt, "dup release");                               \
  NS_ASSERT_OWNINGTHREAD(_class);                                             \
  --mRefCnt;                                                                  \
  NS_LOG_RELEASE(this, mRefCnt, #_class);                                     \
  if (mRefCnt == 0) {                                                         \
    mRefCnt = 1; /* stabilize */                                              \
    _destroy;                                                                 \
    return 0;                                                                 \
  }                                                                           \
  return mRefCnt;                                                             \
}

/**
 * Use this macro to implement the Release method for a given <i>_class</i>
 * @param _class The name of the class implementing the method
 *
 * A note on the 'stabilization' of the refcnt to one. At that point,
 * the object's refcount will have gone to zero. The object's
 * destructor may trigger code that attempts to QueryInterface() and
 * Release() 'this' again. Doing so will temporarily increment and
 * decrement the refcount. (Only a logic error would make one try to
 * keep a permanent hold on 'this'.)  To prevent re-entering the
 * destructor, we make sure that no balanced refcounting can return
 * the refcount to |0|.
 */
#define NS_IMPL_RELEASE(_class) \
  NS_IMPL_RELEASE_WITH_DESTROY(_class, NS_DELETEXPCOM(this))

/**
 * Use this macro to implement the Release method for a given <i>_class</i>
 * implemented as a wholly owned aggregated object intended to implement
 * interface(s) for its owner
 * @param _class The name of the class implementing the method
 * @param _aggregator the owning/containing object
 */
#define NS_IMPL_RELEASE_USING_AGGREGATOR(_class, _aggregator)                 \
NS_IMETHODIMP_(nsrefcnt) _class::Release(void)                                \
{                                                                             \
  NS_PRECONDITION(_aggregator, "null aggregator");                            \
  return (_aggregator)->Release();                                            \
}



///////////////////////////////////////////////////////////////////////////////

/*
 * Some convenience macros for implementing QueryInterface
 */