2 * Copyright 2016 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
21 template <typename Observable, typename Traits>
22 class ObserverCreator<Observable, Traits>::Context {
24 template <typename... Args>
25 Context(Args&&... args) : observable_(std::forward<Args>(args)...) {}
29 Traits::unsubscribe(observable_);
33 void setCore(observer_detail::Core::WeakPtr coreWeak) {
34 coreWeak_ = std::move(coreWeak);
37 std::shared_ptr<const T> get() {
38 updateRequested_ = false;
44 auto newValue = Traits::get(observable_);
46 throw std::logic_error("Observable returned nullptr.");
48 value_.swap(newValue);
51 bool expected = false;
52 if (updateRequested_.compare_exchange_strong(expected, true)) {
53 if (auto core = coreWeak_.lock()) {
54 observer_detail::ObserverManager::scheduleRefreshNewVersion(
61 void subscribe(F&& callback) {
62 Traits::subscribe(observable_, std::forward<F>(callback));
66 folly::Synchronized<std::shared_ptr<const T>> value_;
67 std::atomic<bool> updateRequested_{false};
69 observer_detail::Core::WeakPtr coreWeak_;
71 Observable observable_;
74 template <typename Observable, typename Traits>
75 template <typename... Args>
76 ObserverCreator<Observable, Traits>::ObserverCreator(Args&&... args)
77 : context_(std::make_shared<Context>(std::forward<Args>(args)...)) {}
79 template <typename Observable, typename Traits>
80 Observer<typename ObserverCreator<Observable, Traits>::T>
81 ObserverCreator<Observable, Traits>::getObserver()&& {
82 auto core = observer_detail::Core::create([context = context_]() {
83 return context->get();
86 context_->setCore(core);
88 context_->subscribe([contextWeak = std::weak_ptr<Context>(context_)] {
89 if (auto context = contextWeak.lock()) {
97 DCHECK(core->getVersion() > 0);
99 return Observer<T>(std::move(core));