gecko-dev/xpcom/base/nsIWeakReference.idl

/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 *
 * 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/. */

#include "nsISupports.idl"

%{C++
#include "mozilla/Attributes.h"
#include "mozilla/MemoryReporting.h"

// For MOZ_THREAD_SAFETY_OWNERSHIP_CHECKS_SUPPORTED.
#include "nsDebug.h"

#ifdef MOZ_THREAD_SAFETY_OWNERSHIP_CHECKS_SUPPORTED

#define MOZ_WEAKREF_DECL_OWNINGTHREAD nsAutoOwningThread _mWeakRefOwningThread;
#define MOZ_WEAKREF_ASSERT_OWNINGTHREAD \
  _mWeakRefOwningThread.AssertOwnership("nsWeakReference not thread-safe")
#define MOZ_WEAKREF_ASSERT_OWNINGTHREAD_DELEGATED(that) \
  (that)->_mWeakRefOwningThread.AssertOwnership("nsWeakReference not thread-safe")

#else

#define MOZ_WEAKREF_DECL_OWNINGTHREAD
#define MOZ_WEAKREF_ASSERT_OWNINGTHREAD do { } while (false)
#define MOZ_WEAKREF_ASSERT_OWNINGTHREAD_DELEGATED(that) do { } while (false)

#endif

%}

/**
 * An instance of |nsIWeakReference| is a proxy object that cooperates with
 * its referent to give clients a non-owning, non-dangling reference.  Clients
 * own the proxy, and should generally manage it with an |nsCOMPtr| (see the
 * type |nsWeakPtr| for a |typedef| name that stands out) as they would any
 * other XPCOM object.  The |QueryReferent| member function provides a
 * (hopefully short-lived) owning reference on demand, through which clients
 * can get useful access to the referent, while it still exists.
 *
 * @version 1.0
 * @see nsISupportsWeakReference
 * @see nsWeakReference
 * @see nsWeakPtr
 */
[scriptable, uuid(9188bc85-f92e-11d2-81ef-0060083a0bcf)]
interface nsIWeakReference : nsISupports
  {
    /**
     * |QueryReferent| queries the referent, if it exists, and like |QueryInterface|, produces
     * an owning reference to the desired interface.  It is designed to look and act exactly
     * like (a proxied) |QueryInterface|.  Don't hold on to the produced interface permanently;
     * that would defeat the purpose of using a non-owning |nsIWeakReference| in the first place.
     */
    [binaryname(QueryReferentFromScript)]
    void QueryReferent( in nsIIDRef uuid, [iid_is(uuid), retval] out nsQIResult result );

%{C++
  virtual size_t SizeOfOnlyThis(mozilla::MallocSizeOf aMallocSizeOf) const = 0;

  /**
   * Returns true if the referring object is alive.  Otherwise, false.
   */
  bool IsAlive() const
  {
    return !!mObject;
  }

  nsresult QueryReferent(const nsIID& aIID, void** aInstancePtr);

protected:
  friend class nsSupportsWeakReference;

  nsIWeakReference(nsISupports* aObject)
    : mObject(aObject)
  {
  }

  nsIWeakReference() = delete;

  MOZ_WEAKREF_DECL_OWNINGTHREAD

  // The object we're holding a weak reference to.
  nsISupports* MOZ_NON_OWNING_REF mObject;
%}
  };


/**
 * |nsISupportsWeakReference| is a factory interface which produces appropriate
 * instances of |nsIWeakReference|.  Weak references in this scheme can only be
 * produced for objects that implement this interface.
 *
 * @version 1.0
 * @see nsIWeakReference
 * @see nsSupportsWeakReference
 */
[scriptable, uuid(9188bc86-f92e-11d2-81ef-0060083a0bcf)]
interface nsISupportsWeakReference : nsISupports
  {
    /**
     * |GetWeakReference| produces an appropriate instance of |nsIWeakReference|.
     * As with all good XPCOM `getters', you own the resulting interface and should
     * manage it with an |nsCOMPtr|.
     *
     * @see nsIWeakReference
     * @see nsWeakPtr
     * @see nsCOMPtr
     */
    nsIWeakReference GetWeakReference();
  };