xpcom/base/nsISupportsUtils.h
author Edgar Chen <echen@mozilla.com>
Tue, 17 Sep 2019 01:12:07 +0000
changeset 493515 9596d7f4a7457bccc78cadf9c39bcc9c4b5b97f8
parent 448947 6f3709b3878117466168c40affa7bca0b60cf75b
permissions -rw-r--r--
Bug 1579858 - Should release RefPtr before CollectData is clear; r=smaug mAboutToBeNotifiedRejectedPromises will be clear in AfterProcessMicrotasks() and mPendingUnhandledRejections will be clear after NotifyUnhandledRejections runnable is handled. However, worker could terminate in any time, we still need to clear those structures manually before CollectData is clear. Differential Revision: https://phabricator.services.mozilla.com/D46095

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef nsISupportsUtils_h__
#define nsISupportsUtils_h__

#include "nscore.h"
#include "nsISupportsBase.h"
#include "nsError.h"
#include "nsDebug.h"
#include "nsISupportsImpl.h"
#include "mozilla/RefPtr.h"
#include "mozilla/TypeTraits.h"

/**
 * Macro for adding a reference to an interface.
 * @param _ptr The interface pointer.
 */
#define NS_ADDREF(_ptr) (_ptr)->AddRef()

/**
 * Macro for adding a reference to this. This macro should be used
 * because NS_ADDREF (when tracing) may require an ambiguous cast
 * from the pointers primary type to nsISupports. This macro sidesteps
 * that entire problem.
 */
#define NS_ADDREF_THIS() AddRef()

// Making this a |inline| |template| allows |aExpr| to be evaluated only once,
// yet still denies you the ability to |AddRef()| an |nsCOMPtr|.
template <class T>
inline void ns_if_addref(T aExpr) {
  if (aExpr) {
    aExpr->AddRef();
  }
}

/**
 * Macro for adding a reference to an interface that checks for nullptr.
 * @param _expr The interface pointer.
 */
#define NS_IF_ADDREF(_expr) ns_if_addref(_expr)

/*
 * Given these declarations, it explicitly OK and efficient to end a `getter'
 * with:
 *
 *    NS_IF_ADDREF(*result = mThing);
 *
 * even if |mThing| is an |nsCOMPtr|.  If |mThing| is an |nsCOMPtr|, however, it
 * is still _illegal_ to say |NS_IF_ADDREF(mThing)|.
 */

/**
 * Macro for releasing a reference to an interface.
 * @param _ptr The interface pointer.
 */
#define NS_RELEASE(_ptr) \
  do {                   \
    (_ptr)->Release();   \
    (_ptr) = 0;          \
  } while (0)

/**
 * Macro for releasing a reference to this interface.
 */
#define NS_RELEASE_THIS() Release()

/**
 * Macro for releasing a reference to an interface, except that this
 * macro preserves the return value from the underlying Release call.
 * The interface pointer argument will only be NULLed if the reference count
 * goes to zero.
 *
 * @param _ptr The interface pointer.
 * @param _rc  The reference count.
 */
#define NS_RELEASE2(_ptr, _rc)  \
  do {                          \
    _rc = (_ptr)->Release();    \
    if (0 == (_rc)) (_ptr) = 0; \
  } while (0)

/**
 * Macro for releasing a reference to an interface that checks for nullptr;
 * @param _ptr The interface pointer.
 */
#define NS_IF_RELEASE(_ptr) \
  do {                      \
    if (_ptr) {             \
      (_ptr)->Release();    \
      (_ptr) = 0;           \
    }                       \
  } while (0)

/*
 * Often you have to cast an implementation pointer, e.g., |this|, to an
 * |nsISupports*|, but because you have multiple inheritance, a simple cast
 * is ambiguous.  One could simply say, e.g., (given a base |nsIBase|),
 * |static_cast<nsIBase*>(this)|; but that disguises the fact that what
 * you are really doing is disambiguating the |nsISupports|.  You could make
 * that more obvious with a double cast, e.g., |static_cast<nsISupports*>
                                                           (*
 static_cast<nsIBase*>(this))|, but that is bulky and harder to read...
 *
 * The following macro is clean, short, and obvious.  In the example above,
 * you would use it like this: |NS_ISUPPORTS_CAST(nsIBase*, this)|.
 */

#define NS_ISUPPORTS_CAST(__unambiguousBase, __expr) \
  static_cast<nsISupports*>(static_cast<__unambiguousBase>(__expr))

// a type-safe shortcut for calling the |QueryInterface()| member function
template <class T, class DestinationType>
inline nsresult CallQueryInterface(T* aSource, DestinationType** aDestination) {
  // We permit nsISupports-to-nsISupports here so that one can still obtain
  // the canonical nsISupports pointer with CallQueryInterface.
  static_assert(
      !(mozilla::IsSame<DestinationType, T>::value ||
        mozilla::IsBaseOf<DestinationType, T>::value) ||
          mozilla::IsSame<DestinationType, nsISupports>::value,
      "don't use CallQueryInterface for compile-time-determinable casts");

  MOZ_ASSERT(aSource, "null parameter");
  MOZ_ASSERT(aDestination, "null parameter");

  return aSource->QueryInterface(NS_GET_TEMPLATE_IID(DestinationType),
                                 reinterpret_cast<void**>(aDestination));
}

template <class SourceType, class DestinationType>
inline nsresult CallQueryInterface(RefPtr<SourceType>& aSourcePtr,
                                   DestinationType** aDestPtr) {
  return CallQueryInterface(aSourcePtr.get(), aDestPtr);
}

#endif /* __nsISupportsUtils_h */