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// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef CONTENT_CHILD_SCOPED_WEB_CALLBACKS_H_
#define CONTENT_CHILD_SCOPED_WEB_CALLBACKS_H_
#include "base/callback.h"
#include "base/memory/scoped_ptr.h"
#include "base/move.h"
#include "third_party/WebKit/public/platform/WebCallbacks.h"
// A ScopedWebCallbacks is a move-only scoper which helps manage the lifetime of
// a blink::WebCallbacks object. This is particularly useful when you're
// simultaneously dealing with the following two conditions:
//
// 1. Your WebCallbacks implementation requires either onSuccess or onError to
// be called before it's destroyed. This is the case with
// CallbackPromiseAdapter for example, because its underlying
// ScriptPromiseResolver must be resolved or rejected before destruction.
//
// 2. You are passing ownership of the WebCallbacks to code which may
// silenty drop it. A common way for this to happen is to bind the
// WebCallbacks as an argument to a base::Callback which gets destroyed
// before it can run.
//
// While it's possible to individually track the lifetime of pending
// WebCallbacks, this becomes cumbersome when dealing with many different
// callbacks types. ScopedWebCallbacks provides a generic and relatively
// lightweight solution to this problem.
//
// Example usage:
//
// using FooCallbacks = blink::WebCallbacks<const Foo&, const FooError&>;
//
// void RespondWithSuccess(ScopedWebCallbacks<FooCallbacks> callbacks) {
// callbacks.PassCallbacks()->onSuccess(Foo("everything is great"));
// }
//
// void OnCallbacksDropped(scoped_ptr<FooCallbacks> callbacks) {
// // Ownership of the FooCallbacks is passed to this function if
// // ScopedWebCallbacks::PassCallbacks isn't called before the
// // ScopedWebCallbacks is destroyed.
// callbacks->onError(FooError("everything is terrible"));
// }
//
// // Blink client implementation
// void FooClientImpl::doMagic(FooCallbacks* callbacks) {
// auto scoped_callbacks = make_scoped_web_callbacks(
// callbacks, base::Bind(&OnCallbacksDropped));
//
// // Call to some lower-level service which may never run the callback we
// // give it.
// foo_service_->DoMagic(base::Bind(&RespondWithSuccess,
// base::Passed(&scoped_callbacks)));
// }
//
// If the bound RespondWithSuccess callback actually runs, PassCallbacks() will
// reliquish ownership of the WebCallbacks object to a temporary scoped_ptr
// which will be destroyed immediately after onSuccess is called.
//
// If the bound RespondWithSuccess callback is instead destroyed first,
// the ScopedWebCallbacks destructor will invoke OnCallbacksDropped, executing
// our desired default behavior before deleting the WebCallbacks.
template <typename CallbacksType>
class ScopedWebCallbacks {
MOVE_ONLY_TYPE_FOR_CPP_03(ScopedWebCallbacks, RValue);
public:
using DestructionCallback =
base::Callback<void(scoped_ptr<CallbacksType> callbacks)>;
ScopedWebCallbacks(scoped_ptr<CallbacksType> callbacks,
const DestructionCallback& destruction_callback)
: callbacks_(callbacks.Pass()),
destruction_callback_(destruction_callback) {}
~ScopedWebCallbacks() {
if (callbacks_)
destruction_callback_.Run(callbacks_.Pass());
}
ScopedWebCallbacks(RValue other) { *this = other; }
ScopedWebCallbacks& operator=(RValue other) {
callbacks_ = other.object->callbacks_.Pass();
destruction_callback_ = other.object->destruction_callback_;
return *this;
}
scoped_ptr<CallbacksType> PassCallbacks() { return callbacks_.Pass(); }
private:
scoped_ptr<CallbacksType> callbacks_;
DestructionCallback destruction_callback_;
};
template <typename CallbacksType>
ScopedWebCallbacks<CallbacksType> make_scoped_web_callbacks(
CallbacksType* callbacks,
const typename ScopedWebCallbacks<CallbacksType>::DestructionCallback&
destruction_callback) {
return ScopedWebCallbacks<CallbacksType>(make_scoped_ptr(callbacks),
destruction_callback);
}
#endif // CONTENT_CHILD_SCOPED_WEB_CALLBACKS_H_
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