dom/base/DOMMozPromiseRequestHolder.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef mozilla_dom_DOMMozPromiseRequestHolder_h
   8 #define mozilla_dom_DOMMozPromiseRequestHolder_h
   9
  10 #include "mozilla/DOMEventTargetHelper.h"
  11 #include "mozilla/MozPromise.h"
  12
  13 namespace mozilla::dom {
  14
  15 /**
  16  * This is a helper class that can be used when MozPromises are
  17  * being consumed by binding layer code.  It effectively creates
  18  * a MozPromiseRequestHolder that auto-disconnects when the binding's
  19  * global is disconnected.
  20  *
  21  * It can be used like this:
  22  *
  23  *    RefPtr<Promise>
  24  *    SomeAsyncAPI(Args& aArgs, ErrorResult& aRv)
  25  *    {
  26  *      nsIGlobalObject* global = GetParentObject();
  27  *      if (!global) {
  28  *        aRv.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);
  29  *        return nullptr;
  30  *      }
  31  *
  32  *      RefPtr<Promise> outer = Promise::Create(global, aRv);
  33  *      if (aRv.Failed()) {
  34  *        return nullptr;
  35  *      }
  36  *
  37  *      RefPtr<DOMMozPromiseRequestHolder> holder =
  38  *        new DOMMozPromiseRequestHolder(global);
  39  *
  40  *      DoAsyncStuff()->Then(
  41  *        global->EventTargetFor(TaskCategory::Other), __func__,
  42  *        [holder, outer] (const Result& aResult) {
  43  *          holder->Complete();
  44  *
  45  *          // Note, you can access the holder's bound global in
  46  *          // your reaction handler.  Its mostly likely set if
  47  *          // the handler fires, but you still must check for
  48  *          // its existence since something could disconnect
  49  *          // the global between when the MozPromise reaction
  50  *          // runnable is queued and when it actually runs.
  51  *          nsIGlobalObject* global = holder->GetParentObject();
  52  *          NS_ENSURE_TRUE_VOID(global);
  53  *
  54  *          outer->MaybeResolve(aResult);
  55  *        }, [holder, outer] (nsresult aRv) {
  56  *          holder->Complete();
  57  *          outer->MaybeReject(aRv);
  58  *        })->Track(*holder);
  59  *
  60  *      return outer.forget();
  61  *    }
  62  *
  63  * NOTE: Currently this helper class extends DETH.  This is only
  64  *       so that it can bind to the global and receive the
  65  *       DisconnectFromOwner() method call.  In this future the
  66  *       binding code should be factored out so DETH is not
  67  *       needed here.  See bug 1456893.
  68  */
  69 template <typename PromiseType>
  70 class DOMMozPromiseRequestHolder final : public DOMEventTargetHelper {
  71   MozPromiseRequestHolder<PromiseType> mHolder;
  72
  73   ~DOMMozPromiseRequestHolder() = default;
  74
  75   void DisconnectFromOwner() override {
  76     mHolder.DisconnectIfExists();
  77     DOMEventTargetHelper::DisconnectFromOwner();
  78   }
  79
  80   JSObject* WrapObject(JSContext* aCx,
  81                        JS::Handle<JSObject*> aGivenProto) override {
  82     // We are extending DETH to get notified when the global goes
  83     // away, but this object should never actually be exposed to
  84     // script.
  85     MOZ_CRASH("illegal method");
  86   }
  87
  88  public:
  89   explicit DOMMozPromiseRequestHolder(nsIGlobalObject* aGlobal)
  90       : DOMEventTargetHelper(aGlobal) {
  91     MOZ_DIAGNOSTIC_ASSERT(aGlobal);
  92   }
  93
  94   operator MozPromiseRequestHolder<PromiseType>&() { return mHolder; }
  95
  96   operator const MozPromiseRequestHolder<PromiseType>&() const {
  97     return mHolder;
  98   }
  99
 100   void Complete() { mHolder.Complete(); }
 101
 102   void DisconnectIfExists() { mHolder.DisconnectIfExists(); }
 103
 104   bool Exists() const { return mHolder.Exists(); }
 105
 106   NS_INLINE_DECL_REFCOUNTING_INHERITED(DOMMozPromiseRequestHolder,
 107                                        DOMEventTargetHelper)
 108 };
 109
 110 }  // namespace mozilla::dom
 111
 112 #endif  // mozilla_dom_DOMMozPromiseRequestHolder_h